BULLETIN OF MARINE SCIENCE. 42(1): IH3. 1988

ON THE SIGNIFICANCE OF VARIATION IN A WARM WATER COSMOPOLITAN SPECIES, NOMINALLY CERATOSCOPELUS WARMINGII (PISCES, MYCTOPHIDAE)

Julian Badcock and Teresa M. H. Araujo

ABSTRACT The lantemfish Ceratoscopelus townsendi-warmingii complex is currently recognized as containing two species, C. townsendi, a N.E. Pacific endemic, and C. warmingii, a subtropical- tropical cosmopolite. A comparison of specimens from around a N. Atlantic frontal area, the Azores front (ca. 33°N:32°W), shows that within the area two distinct forms of nominal C. warmingii exist, their separating geographic boundaries more or less coinciding with the frontal boundary. Although considerable variation, particularly that in the number and dis- position of luminescent structures, is known to occur within nominal C. warmingii and to show, in the Atlantic and Indian oceans, some geographic correlations, the situation is more complex than previously appreciated. Comparison of nominal C. warmingii characters, in- cluding larval ones, between specimens from different areas of its geographic range with those of C. townsendi leads to the conclusion that the C. townsendi-warmingii complex should be regarded as comprising a single species, C. townsendi, containing a number of distinct and geographically separated populations. At least 6 variants are distinguishable, represented globally by at least 13 discrete populations, as 6 Atlantic, 3 Indian Ocean and 4 Pacific ones. Boundaries between populations appear to be relatively sharp and such evidence as exists suggests that interpopulation variations are the result of restrictions imposed in some cases by hydrographic barriers and in others by differences in breeding timetables. In reality, while some of the previously recognized cosmopolitan species may comprise a species-complex, others, including C. townsendi, represent a single species composed of a number of distinct and geographically separated populations that show distributional con- cordance with known species assemblages. Insights into how such intraspecific populations arose and are maintained are important in understanding the processes involved in the evolution of communities. For many broadly distributed species, gene flow between intra- specific populations may be rather weak and the population characters themselves an expres- sion of genetic divergence. The zoogeographic implications of this are great but, in particular, appreciation of adaptations across boundary areas will provide valuable insights into com- munityevolution.

Nominally the genus Ceratoscopelus contains three species, C. maderensis (Lowe), C. townsendi (Eigenmann and Eigenmann) and C. warmingii (Liitken). While C. maderensis can readily be separated from the other two species on a number of characters (Nafpaktitis et a1., 1977; Hulley, 1981), distinction between C. town- sendi and C. warmingii rests primarily upon a single feature, the presence or absence, respectively, of supraorbital luminous patches (Nafpaktitis and Nafpak- titis, 1969; Wisner, 1976). In its geographic distribution, C. townsendi is restricted to a small area of the northeastern Pacific, mainly in the California Current region, whereas C. warmingii is essentially a subtropical-tropical cosmopolite (Nafpaktitis and Nafpaktitis, 1969; Wisner, 1976). However, considerable variation, expressed largely as differences in the number and disposition of luminous scales or patches as well as gill raker numbers, exists in C. warmingii and this in itself has led to uncertainty as to whether or not species distinction between it and C. townsendi should be maintained (Bekker and Borodulina, 1968; Nafpaktitis and Nafpaktitis, 1969; Wisner, 1976). Such variation among Atlantic populations has been outlined

16 BADCOCK AND ARAUJO: VARIATION IN CERA TOSCOPELUS 17

briefly (Nafpaktitis and Nafpaktitis, 1969; Nafpaktitis et aI., 1977), if only in a north-south context. Nevertheless, it is possible on the basis of extant literature to identify North Atlantic subtropical, Atlantic equatorial and South Atlantic subtropical populations. During autumn 1980 and early summer 1981 a multidisciplinary program was conducted from RRS DISCOVERYin and around an oceanic frontal region south- west of the Azores (ca. 33°N:32°W). The front probably marks the edge of a southern tongue of the Gulf Stream recirculation, effectively the northeast bound- ary between the eastern and western Atlantic (Fasham et aI. 1985; Gould, 1985), and one objective was to examine the effects such fronts have upon biological communities. e. warmingii is a relatively abundant lanternfish species in this area (Backus et aI., 1977) and was well represented in the biological collections made. Subsequent investigation showed that two distinct forms ofe. warmingii occurred in the area, their separating geographic boundaries more or less coinciding with the frontal boundary. Indeed, the distinction between the two forms is greater in terms of the number of character differences than that apparent between C. lown- sendi and eastern Pacific e. warmingii and, inevitably, the question arose as to whether the two North Atlantic forms represented distinct species. To attempt to resolve this (and the inherent implications any answer must have upon the in- terpretation of the e. lownsendi-warmingii complex) collections from throughout the North Atlantic were examined and aspects of life history studied. This paper reports our findings.

MATERIALSANDMETHODS

The Atlantic material examined comprised 6,506 C. warmingii specimens, including 1,656 larval and transforming stages. Greatest variation in C. warmingii is manifested as differences in the number and disposition of luminescent scales and patches adorning the body (Parr, 1928; Norman, 1930, under C. townsendi; Beebe, 1932, under Lampanyctus polyphotis; Andriyashev, 1962, under C. town- sendi; Bekker and Borodulina, 1968, under C. townsendi; and Nafpaktitis and Nafpaktitis, 1969; Wisner, 1976; Nafpaktitis et aI., 1977, under C. warmingii). As Bekker and Borodulina (1968) point out, however, these structures are easily lost, which makes discernment between natural variations and those due to damage difficult. Even so, it has been the experience of ourselves, as well as of others (Andriyashev, 1962; Nafpaktitis and Nafpaktitis, 1969), that certain luminescent structures, or series of such, remain more persistent than others (Fig. I) and that geographic variation is best assessed through them. Adult specimen lots from throughout the geographic area covered were used to assess potential geographic variation. In addition to observations of the number and disposition ofluminescent scales and patches, counts of AO photophores (photophore designations after Nafpaktitis et aI., 1977), gill rakers on the first arch, and vertebrae were made. Where possible, AO and gill raker counts were taken from both sides of the specimen. Gill raker counts included only definite rakers (see Nafpaktitis et aI., 1977). Vertebral counts were based upon X-radiographs. The results showed that two forms of C. warmingii. designated A and B, were readily distinguishable and consequently all juvenile-adults were assigned accordingly. Capture stations are listed (Appendix I) while the geographic distribution of samples is shown in Figure 2. Vertical distribution was studied from discrete depth samples taken over two seasons and in different parts of the Azores front area (Table 1) using the RMT 1 + 8 multinet system (Roe and Shale, 1979). RMT 8 samples, only, were utilized. The flowmeter system allowed net speed to be maintained at approximately 2k (1.02 m S-I) as well as the subsequent determination of the distance travelled through the water by the net. Catches were consequently standardized as the number of animals caught per km distance (i.e., approximately 8,000 m' water filtered) fished. Animals were sexed and females staged using Merrett's (1971) system of indices. Larval development was traced back from early juvenile stages and followed to early post-flexion. Standard length (SL) was measured to 0.1 mm in larval and transforming stages (terminology of Moser and Ahlstrom, 1970) and to I mm in other stages. For comparison, 28 specimens of C. townsendi were examined. The methods employed in mapping the Azores front area and descriptions of its physical ocean- ography are given by Fasham et aI. (1985) and Gould (1985). 18 BULLETIN OF MARINE SCIENCE, VOL. 42, NO. L, 1988

PLO Gland Dorsal base Supra caudal I )

L---J VO PVO Midventral Y-Gland Prepelvic Gland Figure I. Distribution of photophores and luminescent tissues in nominal C. warmingii.

RESULTS Characterization of Forms A and B. -Although the Atlantic material examined was designated as belonging to either Form A or B, in view of the extent of variation observed overall and possible clinal relationships, the division between the two forms can initially only be regarded as arbitrary, Nonetheless, two char- acters provide 100% separation in adults and consequently it is these that allow evaluation of other, associative characters. Infracaudal luminescent scales and those either side of the anal finbase (Fig, 1) are generic features, yet in Form A these two series remain distinctly separate (with at least one anal finray base visible between the posterior tip of the ultimate anal finbase scale and the anterior infracaudal one, Fig. 3a, b), while in Form B they are contiguous (Fig. 3c) in a fashion reminiscent of that found in C. maderensis. Likewise, a series of lumi- nescent scales running either side of the dorsal finbase (Fig. 1) is conspicuously present only in Form A; in Form B it is absent or, rarely, represented by a series of minute luminescent spots (Fig. 3). There are two characters that tend to be associated particularly with one or other form. First, in Form B there is present a single, well developed, mid ventral and triangular luminescent gland situated between, and extending anterior to, the photophore pair P05 (Figs. 1, 3c). The area beneath it is unpigmented but the shape of the glandular patch is contoured by an intensification of pigment. This differential pigment pattern allowed the determination of whether or not the patch had been present in damaged specimens. A glandular patch as this is characteristic of Indo-Pacific populations (Bekker and Borodulina, 1968; Nafpaktitis and Nafpaktitis, 1969), yet it was rarely found in Form A (0.8% occurrence, N = 4,097), When present in the latter, it was usually small, most often situated posteriorly to P05 and close to the photophore pair Val' while beneath it the area was uniformly brown. In one specimen, the shape, size and position of this patch approached the Form B condition and, furthermore, the area beneath it, though largely unpigmented, had its anterior margin contoured by an intensifi- cation of pigment. Nevertheless, its general absence in Form A, even in specimens with body scales intact, and universal presence in Form B indicates that presence BADCOCK AND ARAUJO: VARIATION IN CERATOSCOPELUS 19

N 50

40

• '0 0 30 • 0 " " " 20

o 10 ------

o o

70 60 50 40 30 20 10 w o 10 E

Figure 2. Geographic distribution of Atlantic material [0, • Form A; T, \1 Form B; i}, 0, Forms A and B (2nd symbol = information from J. E. Craddock)] in relation to surface currents (arrows). Indicated Gulf Stream extensions are (A) system S.E. of Grand Banks, (B) Azores front, (C) Front S.E. of Azores (Gould, 1985). or absence is a function more of individual or population character than of animal capture condition. The second associative character is the number of gill rakers on the first arch: characteristically this is 14 in Form A, in the configuration 4 + I + 9, whereas in Form B it is 15, as 4 + 1 + 10 (Tables 2-3). The summary of meristic characters of Forms A and B (Tables 2-3) demon- strates that not only is variation greater in the former but also that to some extent it is geographically correIa table. Form A specimens from the subtropical North Atlantic tend to have more anal finbase and infracaudalluminescent scales than do those from the equatorial Atlantic (Table 2). The posterior tip of the ultimate anal finbase scale in subtropical North Atlantic specimens ends most frequently below, or slightly anterior to the 6th AOa photophore, with three finray bases clear between it and the first infracaudal scale; in equatorial animals this scale ends more anteriorly, with 4-5 finrays clear (Table 3). Furthermore, and as noted by Nafpaktitis and Nafpaktitis (1969), the infracaudal series in equatorial spec- imens begins well behind the last anal finray, most often below the second AOp, whereas in subtropical North Atlantic individuals it usually starts anterior to the first AOp photophore and often flush with the last anal fint'ay base (Table 3; Fig. 3a-b). 20 BULLETIN OF MARINE SCIENCE, VOL. 42, NO.1, 1988

Table I. "Discovery" biological stations and sampling strategy in Azores front area

No. Station (date) Period samples Sampling depths (tow length, h)

10222 Day 9 20-120; 100-180; 130-205; 200-800 m in 100 m strata (I h) (29-31 :X:80) Night 12 10-120; 90-140; 120-200; 200-1,100 min 100 m strata (I h) 10228 D 12 10-115; 80-130; 128-200; 200-1,100 m as 10222 (I h) (I-3:XI:80) N 12 10-120; 90-140; 120-200; 200-1,100 m as 10222 (I h) 10233 D 12 0-70; 65-97; 90-200; 200-1,100 m as 10222 (1 h) (l4-16:XT:80) N 12 10-90; 80-105; 95-200; 200-1,100 m as 10222 (I h) 10232 N 9 Above thermocline: 43-65; 45-55; 48-53; 45-55; 49-55; 47-51; 40-86; 45-60; 48-58 m (I h) (13-14:XI: 80) 4 At thermocline base: 63-90; 73-92; 60-80; 70-99 m (1 h) 10241 N 8 Around 19°Cisotherm: 90-110; 80-95; 82-100; 85-100; 75--95; (17-19:XI:80) 85-95; 70-95; 68-88 m (I h) 10376 D 18 5-40; 40-60; 60-200; 200-1,700 min 100 m strata (1-1.5 h) (26-30:V:81) N 17 5-25; 25-130; 130-205; 200-1,600 m, as day (1-1.5 h) 10378 D 15 5-50; 50-100; 100-1,400 m in 100 m strata (1.5 h) (7-IO:VI:81) N 15 As day (1-1.5 h) 10379 D 20 5-50; 50-100; 100-1,900 m in 100 m strata (1.5 h) (11-15:VI:81) N 18 As day but to 1,700 m (1-1.5 h) 10380 D 21 5-50; 50-100; 100-1,700 m in 100 m strata; 1,700-2,300 min (16-20:VI:81) 200 m strata (1.5-1.9 h) N 14 As day but to 1,300 m (1-1.5 h) 10382 D 15 5-50; 50-100; 100-1,400 m in 100 m strata (1.5 h) (21-23:VI:81) N 12 As day but to 1,100 m (1-1.5 h)

A tendency exists in equatorial Form A to having less well developed lumi- nescent tissue. This is most easily appreciated through comparisons of the Y-shaped series situated midventrally between the pelvic base and the anus (Fig. 1). The basic structure of this series comprises a linear series of four mid ventral scales with a bilateral posterior pair displaced slightly dorsally. In subtropical North Atlantic animals these scale-like structures are extremely well developed, those of the linear series overlapping (Fig. 3a). In equatorial individuals the pos- teriormost (4th) scale tends to be smaller than the preceding ones and, more often than not, is distinctly separated from them (Fig. 3b), or even missing. Such features were uncommon among subtropical North Atlantic specimens. Moreover, the scales of the bilateral pair are usually much smaller in equatorial than subtropical North Atlantic animals (Fig. 3a-b). Larval Development. - In common with a number of other lanternfish genera, the larva of Ceratoscopelus is round-eyed and slender, with body pigment highly restricted, and one developing the photophores Br2, Vn, PLO and P05 relatively early after flexion (Moser and Ahlstrom, 1972; Shiganova, 1977). No further photophore development occurs until transformation. Post-flexion larval and transforming stages (5.7-18.6 mm SL) were examined from the Azores front (Table 1 stations), an area where juveniles and adults of both forms occur. Larger larvae are readily distinguishable as belonging to C. warmingii by the presence of Br2, Vn, PLO and P05 in conjunction with a distinctive pigment pattern. Pigment is usually restricted as a patch situated dorso-laterally either side of the anal papilla, a deep-seated mid ventral spot immediately posterior to the last anal finray base, and 1-3 spots at the posterior base of the hindbrain (Fig. 4). Only at late trans- forma tion were the two forms separable and then only by virtue of the anal finbase and infracaudalluminescent scale configurations. Slight variations noted in larval pigmentation in the hindbrain and post-anal h : O~~~·o·.·o •• ~h~~-~==--.. ~~ ~

.~ .. ••• o.~ .0000 .. O~

Figure 3. Atlantic forms of nominal C. warmingii: Form A from subtropical N. Atlantic (a) and equatorial Atlantic (b); and Form B (c), subtropical N. Atlantic. 22 BULLETIN OF MAR[NE SCIENCE, VOL. 42, NO. I, 1988

Table 2. Some meristics of C. warmingii Form A (subtropical, tropical and equatorial populations), Form Band C. townsendi (N = number of observations)

No. vertebrae No. anal finbase scales 35 36 37 N 4 N

C. warmingii A subtropical 3 53 29 85 36.3 4 55 213 80 II 0 0 363 C. warmingii A equatorial 3 37 I 41 35.9 I 30 16 2 0 0 0 49 C. warmingii A total 6 90 30 126 5 85 229 82 11 0 0 412 C. warmingii B 3 37 1 41 0 0 1 27 53 4 2 87 C. townsendi 3 19 1 23 0 0 8 11 0 0 0 19 No. gill rakers, Isl arch No. AO photophores

[3 14 [5 [6 N 10 11 12 [3 N C. warmingii A subtropical 55 818 59 0 932 0 20 330 146 2 498 C. warmingii A equatorial 10 84 4 0 98 1 9 75 13 0 98 C. warmingii A total 65 902 63 0 1,030 1 29 405 159 2 596 C. warmingii B 0 15 309 6 330 0 12 124 30 0 166 C. townsendi 0 4 37 5 46 0 5 34 5 0 44 No. supracaudal scales No. infracauda[ scales 4 N 4 6 [0 N C. warmingii A subtrop- C. warmingii A ical 0 6 196 146 13 361 0 0 13 201 186 12 0 412 C. warmingii A tropical 0 4 14 12 0 30 0 7 8 13 10 I 0 39 C. warmingii A equato- C. warmingii A rial 0 0 23 25 1 49 2 13 19 12 0 0 0 46 C. warmingii A total 0 10 233 183 14 440 2 20 40 226 196 13 0 497 C. warmingii B 1 55 65 3 0 124 0 0 0 3 50 55 8 116 C. townsendi 0 2 16 0 0 18 0 0 1 10 8 0 0 19

regions could not be correlated with form. The hindbrain pigment develops later than either the post-anal or anal papilla pigment and initially may be represented as a single mid-line spot, as a pair of bilateral spots or as a bilateral pair with one or more spots about the midline. Gill raker examinations however, showed there to be no relationship between pigment pattern and gill raker configuration. In animals larger than about 14 mm SL this pigment appears as a large, rather diffuse patch. A number of animals had 1-2 deep-seated, midventral spots on the caudal peduncle, in addition to the post-anal spot noted above (Fig. 4). Their transient nature, however, is indicated by a decrease in their incidence with increased animal size (see also Shiganova, 1977). Ahlstrom (1971) examined larvae of C. warmingii and C. townsendi from the Indian Ocean and two areas of the eastern Pacific: "larvae from the three areas were strikingly similar in appearance. Observed differences were mostly in the rate of development, particularly in the sizes at which fin formation took place and at which photophores developed" (Ahlstrom, 1971). A survey of gill-raker configurations among larvae from different station positions shows their propor- tional distributions to be strikingly similar to those of Form A (Tables 3 and 4), as would be anticipated from the low incidence of Form B in these populations. So the brief account below is consequently based largely upon Form A larvae. However, it should be noted that transforming stages of the two forms indicate that larval pigmentation characteristics and the sequences in the development of luminescent organs and glands are identical between the two. BADCOCK AND ARAUJO: VARIATION IN CERATOSCOPELUS 23

Table 3. Gill rakers, AOa and AOp configurations for C. warmingii Forms A and Band C. townsendi (% frequency); position of leading edge of anteriorrnost infracaudal luminescent scale relative to individual AOp photophores (-I signifies position anterior to first AOp, I + between first and second AOp, etc.) in different Form A populations (% frequency)

Gill rakers, Ist arch 3+1+9 3+ I + II 4+1+8 4+1+9 4+1 +10 4+1+11 5+1+10 N C. warmingii A 0.6 5.7 87.6 6.1 1,030 C. warmingii B 0.3 4.5 93.3 1.8 330 C. townsendi 8.7 80.4 8.7 2.2 46 No. AOp

C. warming;; A C. warmingh B C. IOwnsendi No. AOa 4 6 4 6 4 4 0.2 5 2.8 3.9 0.2 2.4 7.2 6.8 29.5 6 1.7 60.6 15.1 4.8 66.3 16.3 47.7 4.5 7 0.3 3.5 11.4 0.3 1.2 1.8 6.8 N = 596 N = 166 N = 44 Position of scale relative to individual AOp

Population -I 1+ 2 2+ 3+ N Subtropical 88.0 10.9 0.8 0.3 661 Tropical 38.2 25.5 12.8 12.8 6.4 47 Equatoria] 6.1 18.4 46.9 14.3 12.2 2.0 49

Table 3. Continued Position of posterior tip of ultimate ana] finbase luminescent scale relative to individual AOa photophores (e.g., 5+ = between 5th and 6th AOa) and the No. of anal finray bases posterior to it in subtropical, tropical (23°-18°N) and equatorial (I ION_50S) populations of Form A (N = observations)

Position of scale relative to individual AOa Subtropical Posterior Post. A rays (No.) 3+ 4 4+ 5+ 6 6+ AOa % Freq.

I 2 4 3 74 12.5 2 I ]6 60 ]1 II 29 19.1 3 ] ]0 20 154 106 10 3 6 46.2 4 9 49 21 41 7 18.9 5 2 7 9 3 1 2.2 % Freq. 0.3 2.5 10.3 6.7 31.9 26.4 3.1 2.5 ]6.2 Tropical 2 2 4.8 3 I 2 12 2 40.5 4 8 4 5 40.5 5 3 3 14.2 % Freq. 7.1 28.7 14.2 40.5 4.8 4.8 Equatorial 2 2.0 3 I 4.1 4 3 6 5 9 49.0 5 I 8 13 44.9 % Freq. 2.0 22.4 38.8 10.2 20.4 4.1 2.0 24 BULLETIN OF MARINE SCIENCE, VOL. 42, NO. I, 1988

.: ..::..::::::::::::.::.::> ;. : .

\ ..... ""

Figure 4, Larvae of nominal C. warmingii from the Azores front area, SL 5.7 mm (upper), 10,9 mm (lower).

In the least developed larva at hand (5.7 mm SL) flexion is just completed but photophores are absent. The pectoral fin is large, spatulate, but as with all fins, rays are undifferentiated. A dorsal finfold extends from slightly anterior to the body midpoint to the caudal, while a ventral one extends likewise from the gut region (Fig. 4). Pelvic bases are indiscernible. Pigment is restricted to the anal papilla and as two midventral spots, one at the posterior end of the presumptive anal fin and one just anterior to the presumptive procurrent rays. Internally, peritoneal pigment is present dorsal to the swimbladder. The caudal finrays differentiate first and, as illustrated by a 6.2 mm SL specimen

which had a full complement of such rays, Br2 appears during this process. In- dividuals with only Br2 and Vn ranged 6.0-6.8 mm SL. In the smallest such animals the anal finrays are just forming, whereas the dorsal remains a finfold continuous with the presumptive dorsal adipose fin. In the largest ones, however, dorsal finrays are differentiated, the dorsal adipose fin is long-based but discrete, and both pectoral and procurrent rays are forming. The pelvic bases, also, are discernible. PLO appears at about this stage (6.8 mm SL) and pas shortly after- wards. Pelvic finrays become discernible by 7.8 mm SL, by which time the remnant ventral finfold in the gut region has disappeared and the dorsal adipose fin becomes short based. Pigmentation of the hindbrain follows and is present almost universally by II mm SL, often at smaller size. Transforming larvae occurred over the size-range 14.5-18.6 mm SL (max. larval size, 16.9 mm SL), transformation being heralded by the appearance of the pho- tophores aPI' OP2 and Br3 in rapid succession, followed by val> POI and A01• The major external manifestations of the transformation period are: the devel- opment and intensification of body pigment, resulting largely in the occlusion of larval pigment; the development of hypaxial muscle in the preventral region; the BADCOCK AND ARAUJO: VARIATION IN CERATOSCOPELUS 25

Table 4. Frequency (% in parentheses) of gill raker configurations in 221 larvae from different Azores front stations

Gill raker configuration Observations Station 4+1+8 4+1+9 4+1+10 (No.) 10228 (EAW) 6 (7.1) 71 (84.5) 7 (8.3) 84 10233 (WAW) 8 (9.0) 74 (83.1) 7 (7.9) 89 10232#19 3 (6.2) 42 (87.5) 3 (6.2) 48 development of supra caudal, infracaudal and anal finbase luminescent scales, and a full complement of photophores. In late transforming forms, POs and VOl are much more prominent than other body photophores. The difference in size of these and the remainder photophores in their respective series is less blatant in early juveniles and this character, together with a clear presence of at least some Y-gland luminescent scales, was used as the yardstick for separating juveniles and late transforming individuals. Development a/Luminescent Tissue. - The various luminescent scales and patches do not develop simultaneously. The deciduous nature of most, however, makes it difficult to elucidate sequences or even the size at which an adult complement is normally attained. The latter aspect is further complicated by individual as well as population variations. Nevertheless, some determination has been pos- sible. The supracaudal is the series first discernible, followed by the infracaudal one, both of which start developing during transformation. The anal finbase series, the Y-gland and, in Form B, the midventral, triangular prepelvic patch all develop early. Indeed, the adult configuration of the anal finbase and infracaudal series was found in all juveniles and late transforming stages. Thus it was possible to separate A and B forms with confidence down to the smallest juvenile size (16 mm SL) examined. Confirmation of this division was provided by gillraker con- figurations coupled with the presence, or clear indications thereof, of the prepelvic patch in Form B juveniles. Whether the scales comprising the Y-gland develop simultaneously or sequen- tially remains uncertain. Among small juveniles, the least number observed was three (the anterior three) and most often so in animals < 18 mm SL. Even so, the adult complement was noted for some individuals < 18 mm SL but this condition was one more general to larger animals. Among such smaller specimens, the anterior three scales were comparatively well developed, the others more weak- ly so. Development of these early formed series is followed by that of the PVO group and, in Form A, the dorsal finbase series. Traces of the ventral patch pair of the former group occurred in individuals as small as 18 mm SL (both forms), whereas clear traces of the dorsal base series were found in most animals > 20 mm SL (Form A). Sequences beyond those outlined above were not determinable. The adult, or near adult, complement was noted in some animals as small as 25 mm SL and usually in those > 30 mm SL. As a generalization, the timing of appearance of particular luminescent structures, as reflected by animal size, and their sequences appear to be similar in both forms. Vertical Distribution and Population Structure. - Ceratoscopelus warmingii is a deep-dwelling lanternfish with a daytime distribution extending well below 1,000 26 BULLETIN OF MARINE SCIENCE, VOL. 42, NO. I, 1988 m depth, and is one remarkable for its extensive diel vertical migrations, partic- ularly so for its well-developed, gas-filled swimbladder (Marshall, 1960; Badcock and Merrett, 1976; Karnella, 1983). The eight vertical distribution series from the Azores front area (Table 1)yielded 1,492 juveniles and adults, of which most were Form A. This is not surprising since it reflects no more than the apparent geographic distribution of the two forms. Thus, in these series, only at St. 10380 was Form B the dominant Cera- toscopelus. The five May-June stations (St. 10376, 10378, 10379, 10380, 10382) yielded 793 Form A specimens. The five individuals from St. 10380 are excluded from the account below. The maximum depths sampled ranged 1,400-1,900 m (Table I). The distributional features shown by the form in the upper 1,400 m, however, were similar between stations and consequently the data have been regarded as a whole. Data standardization based upon flowmeter information counteracted the problem of unequal fishing effort at greater depths. The diurnal distribution extended 700-1,800 m depth but most of the popu- lation lay deeper than 1,000 m. Across the respective 1,000-1,800 m strata, catch rates were relatively even (mean catch numbers ranging 0.61-1.41 animals/km fished) and the population showed neither a preference for particular depths nor any marked stratification of animal size with depth. This situation applied to both males (33-48 mm SL) and females (37-64 mm SL). At shallower depths mean catch rates per stratum varied 0.04-2.75 animals/km fished. The comparatively high final figure, obtained for 800-900 m depth, was due to an exceptionally large catch (57 animals) at St. 10382 that represented 26.5% of the total daytime catch for all four series. The remaining three series gave catch rates of 0-0.19 (mean 0.12) animals/km fished and these are considered more typical for the net (RMT 8) at this depth, time and season. At night the whole population migrated into the upper 200 m with greatest concentration in 50-100 m depth. The length-frequency structure obtained nocturnally in the upper 200 m was very similar to that of the numerically smaller daytime collections and is therefore regarded as being properly representative of the population as a whole. The struc- ture showed a major peak over approximately 36-44 mm SL, composed mainly of males, and a lesser one, mostly female, over approximately 44-52 mm SL (Fig. 5a). Over October-November (St. 10222, 10228, 10233) the length-frequency structure differed radically, being predominated by juveniles of 18-24 mm SL (Fig. 5b). Although the maxim urn depths fished in October-N ovem ber (800-1 , 100 m, day; 1,100 m, night) were shallower than those in early summer, inter-season differences such as the apparent shoaling of the diurnal center of abundance are interpretable on the basis of length-frequency structure and, hence, in an onto- genetic context. Ninety-three specimens were caught by day in the autumn series, one from 600-700 m, the remainder over 700-1,100 m depth. Mean catch rates at equivalent depths were higher than those found in early summer (800-900 m being the exception, but see above), their mean ranging 1.66-5.55 animals/km fished. The day catch was predominated by small juveniles but some size-related depth stratification was apparent. Thus, while juveniles of the dominant mode (Fig. 5b) occurred throughout 700-1,100 m depth, they were concentrated in 700- 800 m (mean animal size, 19.0 mm SL). Mean animal size in deeper strata varied 27.2-30.7 mm SL. The maximum size caught by day was 39 mm SL and larger animals (Fig. 5b) must be presumed to have occupied greater depths. At night, the vast majority of the population migrated into the upper 200 m, mainly the upper 100 m, but in contrast to the early summer situation, some animals (small BADCOCK AND ARAUJO: VARIATION IN CERATOSCOPElJUS 27

15 FOR M A

n=500

0

15

(b) Oct-Nov n=542

0

30 FORM B >- u c: Q) ::l tT Q)

II.."- ~ 15

(c) April-June n=66

o -~ 15

(d) Sept-Nov n=98

o o 20 40 60

Standard Length mm

Figure 5. Size-frequency structures of Forms A and B. 28 BULLETIN OF MARINE SCIENCE, VOL. 42, NO. I, 1988 juveniles) stayed at depth or migrated only short distances. The strata fished in the autumn series were too broad to examine size-stratification of animals in the upper 100 m at night. Good insight, however, is provided at St. 10232 (Table 1) where nets were fished either primarily in the windmixed layer [40-65 (86) m] or at the thermocline base (63-99 m). Above the thermocline, mean animal size was 21.4 mm SL (range 17-43 mm, N = 274) whilst at its base it was 25.5 mm (18-60 mm, N = 412). On the other hand, catch-rates at the thermocline base were far higher than those above the thermocline (27.71 vs. 8.51 animals/km fished). Bearing in mind the population size-frequency structure (Fig. 5b), then, the data indicate that whilst small juveniles can penetrate shallower than sub- adults and adults, their greatest abundance still occurs at or below the thermocline rather than above it. The length-frequency structures for Form B were necessarily derived from all nocturnal collections made in the upper 200 m over April-June and September- November, respectively (Fig. 5c-d). The structures consequently incorporate ma- terial from different years. As with Form A, the strongest autumn peak comprised smalljuveniles (Fig. 5d). Over April-June, and in contrast to the Form A situation over the same season, this peak was maintained (Fig. 5c). The vertical distribution data are lean but they indicate that distributions were similar over both time periods, the shallowest diurnal depth of occurrence being 700 m. Migratory pattern and size-depth relationships were similar to those indicated for Form A in autumn. Larvae were sampled only in the autumn series, whereas transforming stages occurred in both seasons. Larvae occurred in all sampling strata to I, I00 m depth, with their main concentration in the upper 140 m. Within this layer a stratification of animal size with depth occurred, as is emphasized by the collections at St. 10232. Above the thermocline, in depths 40-65 (86) m, mean larval size was 9.7 mm SL (range 6.3-13.5 mm, N = 534) and at the thermocline base, in 63-99 m depth, it was 12.6 mm SL(7.0-14.2 mm, N = 99). Similar size-depth stratifications were found in the Central North Pacific population (Loeb, 1980). As a whole, the data indicate the depth distribution as conforming to the usuallanternfish on- togenetic pattern, in this case rapid larval sinking occurring at about 13.5 mm SL. In depths > 200 m peak larval concentrations occurred in 600-800 m where mean sizes varied 14.6-14.7 mm SL. The autumn transforming stages (N = 94) came from 700-1,100 m depth and showed peak abundance in 900-1,100 m. The identifiable autumn material comprised entirely Form A, whilst both forms were present in the early summer collections. Geographic Distribution in the Azores Front. - The Azores front, which marks the northeastern boundary of the Sargasso Sea 18°C water mass (Gould, 1985) forms a boundary zone for Forms A and B. The position of the front during May 1981 is indicated in Figure 6. In traversing from Eastern Atlantic Water (EAW) to Western Atlantic Water (WAW), the 16°C isotherm deepens from depths < 150 m to ones > 300 m, the front itself being approximately traced by this isotherm at 200 m. The front is probably a permanent structure, but being part ofa dynamic system, its precise location varies temporally (Fasham et al., 1985; Gould, 1985). Consequently, at any given time its exact location in relation to any fishing track is uncertain. Nevertheless, the sampling sites fished in late May and June 1981 were considered to be located in EAW (St. 10379), WAW (St. 10380), along the front (St. 10376) and in a meander (St. 10378). The final site (St. 10382) was placed in a spawning (EAW) eddy that later detached itself(Gould, 1985). In these collections Form B was restricted to WAW (St. 10380) where it comprised 82% of the C. warmingii population (Fig. 6). BADCOCK AND ARAUJO: VARIATION IN CERA TOSCOPELUS 29

36

10~

34

32

30 v A 85'7CX)B 100

S to t ion %A I 10379 100

II 10376 100 gB 100 III 10382 100 28 B 100 IV 10378 100

V 10380 18

36 34 32 30 28 ow

Figure 6. Azores front area: depth (m) of 16°C isotherm (front taken as this isotherm at 200 m) during May 1981 in relation to "Discovery" fishing areas (I-V, May-June 1981), with percentage contribution of Form A or B to nominal C. warrningii population indicated. Open circles represent "Tydeman" stations, April-June 1980, 1983.

In contrast, during the previous autumn Form B had occurred throughout the sampled area of the front. The main sampling sites had been located close to the front but had been regarded as being in EAW (St. 10228), WAW (St. 10233) and intermediate water (St. 10222). At these sites the proportion of Form B varied as only 1.8-4.6% of the C. warmingii population in the upper 120 m at night. A similarly low proportion was found at EAW St. 10241, where eight nocturnal tows (68-110 m depth) were made (Table 1). Here the mean population proportion was 0.6% (sample range, 0-7.1%). On the other hand, in passing across the front from EAW to western influenced water, samples from St. 10232 showed a marked increase in the proportion of Form B with increasing distance from the front. In samples taken above the thermocline, from 40-65 (86) m depth, this increased from 0.5% (range, 0-3.6%) on the eastern side to 60.7% in the "western" sample seemingly farthest from the front. A similar relationship held with samples made 30 BULLETIN OF MARINE SCIENCE, VOL. 42, NO. 1,1988 along the thermocline base at 63-99 m depth. This relationship, however, was not one maintained by larvae. Even across the St. 10232 transect, as shown by the most western sample (#19), no proportional change in gill configuration in favor of that of Form B was noted (Tables 3 and 4). The Tydeman collections (Appendix 1) made in the area during April--early May 1980, September-October 1981 and late May-June 1983 reiterate this geo- graphic pattern, although the biological sampling was not conducted in conjunc- tion with front-mapping. Along 300-32°W and between 24°-36°N, populations containing both forms were found only at about 300-32°N. To the north the population comprised solely Form A, to the south, only Form B (Figs. 2, 6). Geographic Distribution in the North and Equatorial Atlantic. -Compared to that of Form A, the distribution of Form B is highly restricted and known at present as occurring between the longitudes between 200-700W (rarely more easterly) and the latitudes between 23°-34°N (rarely further south) in the east and between 13°- 300N in the west (Fig. 2). Although the more widespread Form A shows consid- erable geographic overlap with Form B, a tendency for mutual exclusion exists, with Form B being unique to the southern half ofthe subtropical gyre. In the mid and eastern Atlantic it is bounded by the Azores front, the Canary and North Equatorial Currents (Fig. 2). West of the Azores front, to about 500W, mixed populations occur over 300-32°N (further west they occur slightly more southerly), whilst to the south only Form B is found (Fig. 2). Thus Form B is the one characteristic of the Southern Sargasso (sensu Backus et al., 1969; 1977; Backus and Craddock, 1977). In this context it is worth noting that Bekker and Borodulina (1968) reported a modal number of 10 gill rakers (incidence 68%, N = 19) on the lower arch of their Atlantic material, a count that is typical for Form B. However, a disproportionate part of their material (66%, N = 80) was collected in the Antilles area within 22°-24°N, 63°-67°W. As pointed out earlier, variation in Form A is to some extent geographically correlatable, specimens from the subtropics characteristically having more, and better developed, luminescent scales. In considering its distribution, it is appro- priate to subdivide Form A into two subcategories; A(i) (subtropical) and A(ii) (equatorial). In doing this we stress that the emphasis placed upon this subdivision is considerably less than that put upon the division Form A-B. A(i) is the char- acteristic Form A (incidence> 95%) throughout the north subtropical distribution area, from the Gulf Stream to the North African coast. In the eastern North Atlantic, the area investigated between l8°-23°N represents a transition one marked by a southerly increased proportion of A(ii) specimens, whilst further south, over 50S-lION, A(ii) (incidence >95%) is characteristic ofthe population. The change in predominance from A(i) to A(ii) thus correlates with the subtropical-tropical faunal boundary that, on the eastern side of the North Atlantic lies in the vicinity of the Cape Verde Islands (Backus et al., 1965, 1970, 1977; Foxton, 1971/72; Fasham and Angel, 1975; Backus and Craddock, 1977; Badcock and Merrett, 1977). Dr. J. E. Craddock (Woods Hole Oceanographic Institution) kindly pro- vided us with information regarding the distributions of A(i) and A(ii) in the western North Atlantic. The samples he examined showed that A(ii) occurred in the Caribbean (90% proportion), the Straits of Florida (100%) and in the Florida Current off St. Augustine (ca. 50%). In Slope Water and the Gulf of Mexico, A(i) predominated over A(ii) while pure populations of A(i) occurred in the Northern Sargasso (300N, 67°05'W) and warm core Gulf Stream rings. Form A extends to at least 160S in the eastern Atlantic but south of this a Form at present indistinguishable from Form B occurs (Nafpaktitis and Nafpaktitis, BADCOCK AND ARAUJO: VARIATION IN CERATOSCOPELUS 31

1969; Nafpaktitis et a1., 1977; J. E. Craddock, pers. comm.). Overall, the obser- vations on the distribution of Form A are concordant with the view that A(ii) is widespread in the equatorial Atlantic and that its presence in the Florida Current- Gulf Stream system represents entrainment from the western tropics. Likewise the presence of A(i) in this system and in warm core rings is consistent with entrainment from the Northern Sargasso. The population in the Gulf of Mexico may embody a semi-isolated one but this aspect requires more thorough inves- tigation. As pointed out by Backus et a1. (1977), the Gulf of Mexico contains populations of several species which in the western Atlantic tend to be excluded from the southern subtropics and have temperate-semisubtropical and subtropical Atlantic distribution patterns (see also Nafpaktitis et al., 1977). Whether or not these populations represent sterile expatriates is unknown even though the larvae of three, Hygophum hygomii (Liitken), H. benoiti (Cocco) and Ceratoscopelus maderensis have been reported from this area (Richards, 1984). The situation of C. maderensis is even more enigmatic in that though larvae have been caught in the eastern Gulf of Mexico and the Caribbean, adults are unknown in both areas (Richards, 1984).

DISCUSSION Synonymy ofe. warmingii with e. townsendi. - The C. townsendi species-complex is currently regarded as containing two species, C. townsendi and C. warmingii (Nafpaktitis and Nafpaktitis, 1969; Wisner, 1976). The characters uniting and thus separating this complex from C. maderensis are the presence ofthe Y-gland, that of a large luminescent patch below the PLO photophore, a low gill raker number [14-15 (13-17) vs. 19-22 (18-21)], and the lack ofa supra-orbital spine. By using as criteria the presence or absence of luminescent tissue along the dorsal base in conjunction with that of the midventral prepelvic gland, and configurations of the anal finbase and infracaudal series, at least four "kinds"· of C. warmingii emerge from the literature, each one having an apparently unique combination of these variants and a distinct geographic distribution (Table 5). Three "kinds" bear the prepelvic gland, but either the anal finbase and infracaudal series are separated and the dorsal fin series is present (Fig. 7a), or else they are contiguous, the dorsal finbase series being present or absent (Figs. 7b and 3c). The fourth "kind", typified by Form A (Fig. 3a-b), lacks the prepelvic gland, has a dorsal finbase series, and separated anal finbase and infracaudal series. The type specimen of C. warmingii conforms with this form (J. G. Nielsen, pers. comm.). Dr. J. E. Craddock informs us that specimens from near the Subtropical Convergence of the South Atlantic (33°S, 46°W and 35°S, 18°W)also lack the prepelvic gland and have a dorsal finbase series (albeit weakly developed) but that the anal finbase and infracaudal series are usually contiguous (one scale sometimes missing). Con- sequently, they represent a fifth "kind" of C. warmingii. The combination of these characters in C. townsendi differs from all the preceding ones: the prepelvic gland is present, the anal base and infracaudal series are separate, and the dorsal finbase series is usually absent (Table 5; Fig. 7c). The literature is conflicting regarding the presence or absence of the dorsal finbase series. Neither Bolin (1939) nor Nafpaktitis and Nafpaktitis (1969) note any such luminescent tissue but Wisner (1976) states it to be present. This series is easily damaged yet, as is amply

I ••Kind" is applied here because the level of characterization is necessarily coarser than that given for Forms A and B. Although ultimately a Form and "Kind" may prove to be synonymous, in the present absence of better meristic and distributional data only Form A is unequivocally so. 32 BULLETIN OF MARINE SCIENCE, VOL. 42, NO. I, 1988

Table 5. Characters of the "kinds" of nominal C. warmingii vs. C. townsendi

Midventral Dorsal prepelvic finbase Anal finbase-infra- gland series caudal configuration Ocean occurrence C. warmingii I Present Present Separated Indo-Pacific 2 Present Present Contiguous N.W. Pacific 3 Present Absent Contiguous Atlantic, Indo-Pacific 4 Absent Present Separated N. subtropical and equatorial Atlantic 5 Absent Present Usually S. Atlantic, subtropical convergence contiguous C. townsendi Prcsent Usually Separated N.E. Pacific absent demonstrated by our C. warmingii material, when conspicuously present in vivo some scales usually survive capture abrasion. In the C. townsendi material we examined most specimens lacked this series completely but in some minute (and in one specimen, conspicuous) traces ofluminescent tissue occurred. Consequent- ly, in C. townsendi considerable variation in this character may exist, from the series being poorly developed but conspicuously present, to it being totally absent. The systematic infegrity of the character combinations outlined above, however, is undermined by the variations expressed in C. warmingii Forms A and B, especially when comparisons are restricted to exclude tropical and equatorial specimens of Form A. For example, 25% of individuals from the North Atlantic subtropical material had 5-6 anal finbase luminescent scales (vs. 92% in Form B) and a substantial proportion (12.5%) had only one anal finray base separating this series from the infracaudal one (Tables 2-3). Likewise, a number of Form B specimens bore inconspicuous traces ofthe dorsal base series (Fig. 3c). Moreover, the archetypal Form A lacks a midventral prepelvic gland, yet this lack is not entirely universal within the form. It is occasionally present « I% incidence), in N. Atlantic subtropical material but even then is rarely well developed. The bias towards expression of character intermediate between Forms A and B is com- pounded in these particular specimens by an increased proportion of individuals with 5-6+ anal finbase scales and only one ray separating the anal finbase and infracaudal series, relative to that found generally in North Atlantic subtropical Form A (Table 6). Two such specimens had in addition 1-2 small patches situated midventrally between the PO photophores. A larger number of Form A specimens (2% incidence, N = 4,097), while lacking the prepelvic gland, bore 1-5 similar patches in a series running midventrally from just anterior to POI to POs. This series was found in neither Form B nor equatorial Form A [i.e., A(ii)] but An- driyashev (1962) described a comparable one in southeast Pacific specimens that on all other characters seem indiscernible from Form B. Moreover, a single an- terior patch was noted in one specimen of the C. townsendi examined. Overall, these comparisons suggest the apparent uniqueness of the character combinations of the five "kinds" of C. warmingii to be the product of different degrees of expression of characters present in all populations and, hence, that only one species is involved. By the same token, specific significance cannot be attached to the different combination observed in C. townsendi. What is more, other char- acters suggested by Nafpaktitis and Nafpaktitis (1969) as being possibly diagnostic for species separation of Indo-Pacific populations of the C. townsendi-complex have since proved unreliable (Wisner, 1976), leaving the presence or absence of supraorbital glands as the sole adult character that differentiates the species. BADCOCK AND ARAUJO: VARIATION IN CERATOSCOPELUS 33 a

, ~_) \.,or-__ -_~ - 0 __------.------0 '""o·~ -'~v·~"<:.;..'"00.

Figure 7. Nominal C. warrningii from (a) northern Indian Ocean (lO"09'N, 59°55'E), (b) N.W. Pacific (38°34'N, 144°17'E). (c) C. townsendi sensu strictu, N.E. Pacific (28°55'N, 118°08'W). After Nafpaktitis and Nafpaktitis, 1969 (a, c) and Bekker and Borodulina, 1968 (b). 34 BULLETIN OF MARINE SCIENCE, VOL. 42, NO. I, 1988

Table 6. Nominal C. warmingii Form A with prepelvic midventral gland: (i) gill raker configuration, Ist arch; No. infracaudal (ii) and anal finbase (iii) luminescent scales. Relative positions of anterior- most part of 1st infracaudal scale (iv) and of posterior tip of ultimate anal finbase scale (v) (see legend, Table 3). N = number of observations

(i) Gill raker configuration (iii) Anal finbase scales (No.)

4+1+8 4+1+9 4+1+10 N 4 6 N

Frequency I 51 8 60 3 II 9 2 I 26 % 1.7 85.0 13,3 11.5 42.3 34.6 7,7 3.8 (ii) Infraeaudal scales (No.) (iv) Position of scale relative to individual AOp N -I 1+ N

Frequency I 10 16 27 25 3 I 29 % 3.7 37.0 59.2 86.2 10.3 3.4

(v) Position of scale relative to individual AOa Anal rays (No.) 4 4+ 5+ 6+ Post AOa % Freq.

I 5 17.2 2 I 3 2 24.3 3 9 3 I 48.2 4 I 3.4 5 I I 6.9 % 3.4 6.9 3.4 31.0 13.8 10.3 3.4 27.6

Moser and Ahlstrom (1970, 1972, 1974) have clearly demonstrated the value of larval studies to myctophid systematics and they and others (largely cited by Moser et aI., Table 61, 1984) have shown that distinctive larval morphologies and pigment patterns allow the separation of most species. This specific distinct- ness is often maintained between closely-related, allopatric species that superfi- cially are extremely alike in adult stages [e.g., Protomyctophum (H.) crockeri- complex; cf. Moser and Ahlstrom, 1970, 1974; Wisner, 1976]. Among widespread species, however, larval geographic variations are manifested as differences in development rates and sometimes by minor differences in pigmentation (Pertseva- Ostroumova, 1974). Within the C. townsendi-complex, larvae from different, widely separated areas are likewise indistinguishable in their morphologies and pigmentation. Indeed, Ahlstrom (1971) observed similarities to be greater between the larvae of C. townsendi and nominal C. warmingii from the eastern Pacific than between those of nominal C. warmingii from the Indian Ocean and south- eastern Pacific. Correspondingly, the basic larval pigmentation shown by Shiga- nova's (1977) and our Atlantic material appears indistinguishable from that de- scribed by Belyanina (1982) in material from the western tropical Pacific and Indo-Australian archipelago. Nor were we able to distinguish on pigment pattern alone, transforming stages of C. warmingii Forms A and Band C. townsendi, all of which still retained the basic larval pigmentation. Together the adult variations and larval similarities observed here render the prevailing two-species concept for the complex as questionable, especially since the geographic distribution of the complex itself is continuous throughout most of the subtropical-tropical belt of the world ocean (Fig. 8). The species warmingii entered the literature by default in the sense that Liitken (1892) described it without reference to C. townsendi and only much later (Parr, 1929; Bolin, 1939) were supraorbital glands noted in the latter species. At the time of Nafpaktitis and Nafpaktitis' (1969) resurrection of C. warmingii little data were available to BADCOCK AND ARAUJO: VARIATION IN CERATOSCOPELUS 35

°0 36 BULLETIN OF MARINE SCIENCE, VOL. 42, NO. J, 1988 give due regard to developmental, seasonal and ecological aspects of the complex. Yet such information is essential in determining the systematics of a species- complex. Maintenance of the two species as distinct (Nafpaktitis and Nafpaktitis, 1969; Wisner, 1976) has been influenced primarily by the presence of supraorbital glands in C. townsendi and, secondarily, by the geographic restriction of this species to an area with a distinctive fauna that includes some endemic taxa. For the reasons outlined below we consider this separation at species level to be no longer justifiable and therefore regard C. warmingii as a junior synonym of C. townsendi. The transitional California Current area of the northeastern Pacific has a char- acteristic fauna containing a number of strictly transitional water species in several distributional patterns, as well as boreal and subtropical-tropical elements of which some are widespread (Berry and Perkins, 1966; Moser and Ahlstrom, 1970; Wisner, 1976; Johnson, 1982). In this way the fauna has parallels with that associated with the Mauritanean Region of the Atlantic (Backus et al., 1977; Badcock, 1981). Although C. townsendi shows a distributional concordance with several far-neritic species (sensu Parin, 1984) [e.g., Diaphus theta Eigenmann and Eigenmann; Lampanyctus ritteri (Gilbert); Protomyctophum (H.) crockeri (Bolin)], this reflects only the degree of isolation of the population rather than provide any implications regarding the species composition of the complex, even when the luminescent characteristics of the population are taken into account. Restricted distributions are not unusual within the complex and several kinds occur only in parts of one ocean, whereas just one is found in parts of all oceans (Table 5). One consequence of this is that particular luminescent features are geographially lim- ited. Animals lacking the preventral gland, for example, are unique to the Atlantic (Table 5); even so, the presence or absence of the preventral gland has no taxo- nomic significance at the species level. Of greater consequence is that since the geographic distribution is continuous, the potential for interaction between "kinds" exists across their shared boundary areas, a potential that is enhanced by the similarities in vertical distribution and migratory behavior of the various "kinds" (Bekker and Borodulina, 1968; this study). In contrast, it is usual among closely- related species for relative isolation to be maintained in areas of geographic overlap by vertical segregation [e.g., among lanternfishes c.f. Diaphus hudsoni Zubrigg and Scott, D. meadi Nafpaktitis; Lepidophanes gaussi (Brauer), L. guentheri (Goode and Bean); Triphoturus mexicanus (Gilbert), T. nigrescens (Brauer): Nafpaktitis et al., 1977; Hulley, 1981, 1986]. Isolation may be further compounded by sibling species having different spawning seasons (Hulley, 1981). Certainly a tendency towards reproductive isolation exists between adjacent populations within the C. townsendi-complex (as is indicated in the size-frequency structures of Forms A and B, Fig. 5) but there is no evidence that this is any better developed between C. townsendi and adjacent populations of C. warmingii. In year-round collections, Moser and Ahlstrom (1970) found larval C. townsendi to show peak abundances over the summer months but to be absent only during November-December. Near Hawaii C. warmingii has a spring peak-spawning period (Clarke, 1973), whilst its larvae provide a substantial year-round contribution to the ichthyo- plankton of the Central North Pacific (Loeb, 1980). The parallels apparent in the expression oflarval geographic variations between widespread species and the C. townsendi-complex at present do little to clarify the species situation since species distinction oflarvae within a few other broadly distributed species-complexes is likewise currently impossible, or questionable, on morphological and pigmentation characteristics (e.g., Benthosema pterota-, Centrobranchus nigro-ocellatus-, Tarletonbeanis crenularis-complexes: Moser and BADCOCK AND ARAUJO: VARIATION IN CERATOSCOPELUS 37

Ahlstrom, 1970, 1974; Pertseva-Ostroumova, 1974; Tsokur, 1981). Taxonomi- cally these complexes are problematic (Bekker, 1964; Wisner, 1976) and represent just one anomaly in our understanding of larval and adult taxonomies yet to be rationalized. As an example, Nafpaktitis (1973) and Tsokur (1981) respectively offered adult and larval distinctions for the two species of the B. pterota-complex (which has a disjunctive distribution) and in both cases characterized B. pterota (Alcock) on the basis of material collected from a small area within the broader distribution range of the species. Subsequent observations on adults (Wisner, 1976; Gjesaeter and Beck, 1981) have indicated not only geographic variation within the species but also that variation is far greater, showing considerable overlap with B. panamense (TAning),than was appreciated by Nafpaktitis (1973). Consequently before B. panamense can be confirmed as a distinct species, a further evaluation of larval and adult variation in B. pterota is required. Whilst we find little evidence to encourage viewing the complex other than as one containing a single species, C. townsendi, with several forms, in common with others (Bekker and Borodulina, 1968; Nafpaktitis and Nafpaktitis, 1969) we rec- ognize that C. townsendi sensu strictu represents the most isolated population of the complex. Equally, we acknowledge that this degree of isolation may ultimately prove sufficient to warrant the recognition of C. warmingii as a valid species. However, at present the distribution of the various "kinds" are poorly known for the Pacific (see next section) and, notwithstanding an absence of supraorbital glands, the luminescent characteristics of the subtropical population(s) adjacent to that of C. townsendi have yet to be determined. Furthermore, the supraorbital glands themselves are easily lost (Bolin, 1939; Wisner, 1976), rendering any de- velopmental cline that may exist in this character (as occurs, for example, with the prepelvic gland) extremely difficult to detect. Thus the taxonomic significance of supraorbital glands remains to be established.

Comments on the Geographic Distribution of c. townsendi Populations. - Cera- toscopelus townsendi is a warm water cosmopolitan species. In considering such, Gibbs et al. (1983) suggest "that closer taxonomic study of widespread 'species' may reveal several species (or different entitities) being confounded under a single name and that the concept of a single circum-global tropical-sub-tropical region may not be justified." However, on the basis of our evidence, particularly that from the tropical and North Atlantic, a subdivision of a nominal C. townsendi- complex cannot at present be substantiated, at least, not at species level. Even so, the evidence indicates the species to comprise a number of recognizable forms and geographically discrete populations. Outside the tropical and North Atlantic Ocean, the data available are rather poor but, tentatively, the six "kinds" of C. townsendi (Table 5) are represented worldwide by at least 13 populations, as 6 Atlantic, 3 Indian Ocean and 4 Pacific ones (Fig. 8). The distribution of Atlantic populations shows a coherency that equates rea- sonably well with the zoogeographic scheme initially presented by Backus and Craddock (1977), and further elaborated upon by Backus et al (1977). In the North Atlantic, Form B is to be found mainly in the Southern Sargasso Sea province of these authors. The occurrence of the equatorial Form A(ii) in the Guinean, Ca- ribbean and Straits of Florida provinces (to at least I60S in the Guinean province, J. E. Craddock, pers. comm.) suggests a continuous, single, population throughout their Tropical Region. The subtropical North Atlantic Form A(i) manifests itself as two geographically separated populations, one occurring across the northern subtropics (Northern Sargasso Sea, North African Subtropical Sea provinces) and one in the Gulf of Mexico. As indicated earlier, the status of the latter population 38 BULLETIN OF MARINE SCIENCE, VOL. 42, NO. I, 1988 is uncertain. A fifth Atlantic population of members indistinguishable from Form B may be more or less restricted to the South Atlantic Subtropical Region. Nafpak- titis et al. (1977) noted such specimens from about 160S(no longitude given) and J. E. Craddock (pers. comm.) notes similar ones from about 180S, 300W and 23°S, 32°W. Further south this form is replaced by yet another kind (Table 5 and Fig. 8) that presumably forms a peripheral population associated with the Subtropical Convergence. The distribution and member characters of Indian Ocean populations are in- dicated in Figure 8, based upon the data of Bekker and Borodulina (1968) and Nafpaktitis and Nafpaktitis (1969). Along approximately 600-65°E, the latter au- thors noted boundary areas around 80S and 27°S, with specimens to the north and south having similar luminescent scale arrangements (Fig. 7a) and geograph- ically, sandwiching a form akin to Form B (Fig. 8). This pattern correlates with the geographic variation of the number of gill rakers on the lower gill arch observed by Bekker and Borodulina (1968). These authors found 9 gill rakers in specimens from the northern and northeastern Indian Ocean, including the Indo-Malaysian Archipelago, whereas to the south there were 10. There are at least four "kinds" of C. townsendi present in the Pacific, all of which characteristically bear 10 gill rakers on the lower gill arch and have a prepelvic gland. Although the species occurs across large areas, from about 400N-400S (Bekker and Borodulina, 1968; Wisner, 1976), only for one kind, (Fig. 7c), that occurring in the transition region off California (Wisner, 1976), can the distribution be reasonably mapped (Fig. 8). Of the other "kinds," Bekker and Borodulina (1968) illustrate one, captured at 38°34'N, 144°l7'E (Fig. 7b), and note that in- dividuals of the population within the Pacific northwestern circulation tend to have more AOp photophores (6) than others from elsewhere. As cited earlier, Andriyashev (1962) describes another "kind" very akin to Form B from the southeast Pacific. He reported four specimens from 37°55'S, 109°24'W and one from Antarctic waters in 64°36'S, 108°52'W. The animals collected by Craddock and Mead (1970) off Central Peru (ca. 34-3loS, 77°-92°W) were similar to An- driyashev's (J. E. Craddock, pers. comm.). Finally, a fourth Pacific "kind" and population is known from specimens recently collected in the Solomon Sea by G. R. Harbison (Woods Hole Oceanographic Institution). These animals are very similar to those described and illustrated by Nafpaktitis and Nafpaktitis (1969) from the northern Indian Ocean (Fig. 7a) but characteristically have 4 + I + 10 gill rakers on the first arch (J. E. Craddock, per. comm.). As is exemplified by the changeover of Forms A and B in the Azores front area, boundaries between distinctive populations of C. townsendi appear to be relatively sharp. Across the Azores front, the major hydrographic changes occur in the upper 300 m (Fasham et al., 1985; Gould, 1985) and thus within the realm where much of the larval phase is spent. Meristics are fixed during egg and larval periods and can be influenced by a number of environmental factors (Blaxter, 1969). With deep-sea fishes, however, determination of whether variation is the consequence of environmental or genetic influences relies almost entirely upon circumstantial evidence. Such evidence as exists for C. townsendi supports the hypothesis that inter-population variations result from a restriction in gene flow and hence are genetic manifestations. In this context, the simplest example to cite is that found in the eastern Pacific, where the abundant northeastern and southeastern popu- lations are separated by an area effectively sterile for C. townsendi, the oxygen deficient waters of the equatorial zone (Ahlstrom, 1971; Wisner, 1976). On the other hand, where the boundaries of two distinct populations are confluent, as in the North Atlantic subtropics, the most potent factor encouraging genetic isolation BADCOCK AND ARAUJO: VARIATION IN CERATOSCOPELUS 39 may be the difference that exists in breeding timetables. Although the data avail- able are limited, on the basis of population length-frequency structures (Fig. 5) and larval incidence, the peak breeding period of Form A in the central and eastern Atlantic occurs over late summer and autumn, whilst that of Form B is much broader and may not even be seasonally tied. Moreover, whilst batch fecundity in this species can vary area to area (Clarke, 1984), the few ripe egg counts we were able to make suggest fecundities in Forms A and B to be similar (ca. 2,500-3,500/0vary pair, SL53-64 mm). The implications are two-fold: firstly, that the seasonal pulsing of the reproductive cycle in Form A compared to the temporally more broadly spread one in Form B, will allow only a low level of potential interbreeding; secondly, that the resultant dilution of genetic interchange is not compensated for by an increased fecundity of one or the other form. Biomass across the Azores front was found to be much lower in Western than Eastern Atlantic Water (Angel and Fasham, 1983), a situation reflected also by C. townsendi, through the change in predominance of form. The much lower population density of Form B will inevitably further enhance the trend towards its isolation from Form A. However, further west, Backus et ai. (1969) found C. townsendi to be extremely abundant either side of the frontal area separating the Northern and Southern Sargasso. Consequently, with respect to isolating mech- anisms, differences in abundance, although important, may be less so than those in breeding timetables. There has been an increasing awareness that of the many species previously recognized as being broadly distributed, in reality some comprise a species-com- plex, whilst others represent a single species with a number of distinct and geo- graphically separated populations; and that the latter show a marked distributional concordance with the faunal patterns of species with restricted distributions (Ebel- ingand Weed, 1963; Baird, 1971; Johnson and Barnett, 1975; Nafpaktitis, 1978; Badcock and Baird, 1980; Badcock, 1981; Johnson, 1982; Gibbs et aI., 1983; Johnson and Feltes, 1984). Notwithstanding the reservations of Gibbs et ai. (1983) and an awareness that an inability to distinguish species within a complex does not necessarily deny their existence, some species do span much of the oceanic subtropical and/or tropical regions. Apart from C. townsendi, these include the likes of the lanternfish Notolychnus valdiviae Brauer, the hatchetfishes, Argyro- pelecus hemigymnus Cocco, and most Sternoptyx spp., the photichthyid Vinci- guerria nimbaria (Jordan and Williams) and certain gonostomatid eye/othone spp., some of which are known to exhibit geographic meristic and morphometric variation and all of which are abundant throughout much of their respective geographic distributions (Mukhacheva, 1964; 1974; Baird, 1971; Nafpaktitis et aI., 1977; Badcock and Baird, 1980; Badcock, 1982; Johnson, 1986). Despite the obvious attributes of such cosmopolitan species and the relative ease with which many can be captured in large numbers, their potential value as zoogeographic tools has been vastly underrated. What limited information is available (Johnson and Barnett, 1975; Johnson, 1986; this study) indicates that regardless of their ubiquitous nature, across the broad ranges of their geographic distribution such species are responsive to environmental change and, hence, sensitive to boundary areas, resulting in the partial isolation of distinct populations. Since there is apparent concordance in the distributions of intra-specific populations and species assemblages, how these intra-specific populations arose and are maintained as more or less separate entities are questions fundamental to an understanding of the processes involved in the evolution and perpetuation of species assemblages. The deficiencies in this study illustrate some of the problems in attempting an- swers. Thus, while we have identified a number of C. townsendi populations, 40 BULLETIN OF MARINE SCIENCE, VOL. 42, NO. I, 1988 geographically we have been able to delineate but a few. The greatest deficiency in our data, however, is that in breeding cycle information, particularly in the context of adjacent populations, since this is critical to any assessment as to whether or not a character change is merely ecophenotypic. Although our evidence suggests that C. townsendi should be regarded as comprising a number of sub- species, we refrain from allocating these for the lack of good comparative de- scription and, in most cases, adequate geographic coverage. Even in the Atlantic, where it is clear that Forms A and B are distinct subspecies, within Form A the relationships of A(i) and A(ii) remain uncertain. Despite these difficulties, the theme emerging here and elsewhere (Karnella and Gibbs, 1977; Badcock, 1981; Johnson, 1986) remains one suggesting that for many broadly distributed species gene flow between allopatric, intra-specific pop- ulations (with distribution patterns corresponding to those of species assemblages) is rather weak and consequently that the population characters themselves are an expression of genetic divergence. The implications for zoogeography are manifold; but in particular, an appreciation of the intra-specific morphophological and bi- ological (aspects of life history, reproductive strategy, behavior, feeding ecology) adaptations to the different environmental conditions across physical boundaries provides insights into the interaction of communities (or parts thereof) at bound- aries, the mechanisms involved that maintain community integrities and hence those that may have been, and continue to be, significant in community evolution.

ACKNOWLEDGMENTS

Our thanks are extended to G. E. Maul (M.M.F.), S. van der Spoel, Trudie Pafort van lersel (I.T.Z.), J. G. Nielsen (Zoological Museum, Copenhagen), G. E. Swinney (R.S.M.) and their institutions for providing ready access to material in their care, especially to Trudie and her family for their kind hospitality in Amsterdam; to M. V. Angel (1.0.S.), J. E. Craddock (W.H.O.I.), P. A. Hulley (South African Museum, Cape Town) and J. R. Paxton (The Australian Museum, Sydney) for useful and constructive discussion of the draft manuscript, and to Mrs. R. Russell for her illustrations. We are particularly indebted to J. E. Craddock who freely gave of information without which this study would have been far shallower.

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DATEACCEPTED: March 17, 1987. BADCOCK AND ARAUJO: VARIATION IN CERA TOSCOPELUS 43

ADDRESS: Institute oj Oceanographic Sciences, Wormley, Godalming, Surrey, GU8 5UB, United Kingdom; PRESENT ADDRESSES: (T.M.H.A.) Laborat6rio de Investigaqao das Pescas, Rua da Mouraria, 31, 9000 Funchal, Madeira, Portugal; (J.B.) 17 High Street, Boxsall, Nr. Matlock, Derbyshire, 4D lAS, United Kingdom.

ApPENDIX I

Atlantic material examined: Ship, station number, position, number of animals/type (A, Form A, B, Form B, L. transforming and larval stages). I.O.S., Institute of Oceanographic Sciences, Wormley; I.T.Z., lnstitut voor Taxonomische Zoologie, Amsterdam; M.M.F., Museu Municipal do Funchal, Madeira; R.S.M., Royal Scottish Museum, Edinburgh.

Eastern subtropical Atlantic (E. of 25°W) I.O.S.: "Discovery" St. 4760, 30"38'N:21"36'W, A 101, B7; 5822. 28"02'N:16"I7'W, A 245; 6199, 36"30'N: IO"W, A 29; 7856 #37, 51, 300N:23°W, A 75; 8262, 32"OS'N:16°14'W, A 10; 8263. 32"06'N: 20"26'W, A 10; 8264, 32"11 'N:23"49'W, A 12; Il036, 39"2S'N:IS"OS'W, A I; Il045 #2,3, 39°30'N: IS"W, A 5; Il086 #2, 4S"00'N:IS"OS'W, A I; Il089 #1,2, 39°43'N:IsoI3'W, A 2; Il090 #1, 2, 39°42'N:Iso07'W, A 2; Il092 #1-3, 39"40'N:I S"W, A 17. I.T.Z.: "Tydeman" ITZ Project lOlA St. 54 #11, 26°08'N:24°3I'W, A 93, B 5; 55 #1, 27°10'W: 19°5S'W, A 21. M.M.F.: "Discovery" St. 4758, 28°01'N:16"46'W, A 73; "Challenger" St. February 1979, St. 30, 32"12'N:I7"S3'W, A II; 31. 32°16'N:18"03'W, A 12; 34. 32"19'N:18°24'W, A 9; 39, 32°N:18°W, A 3; 40, 32"N:I 8"W, A 20; 41, 32"S4'N:16°47'W, A I I; 42, 32°S8'N:16°46'W, A 33; 46, 33"03'N:16"30'W, A 69; 48, 32°SS'N:16°3S'W, A 95; 51, 32"S8'N:16"46'W, A 2. R.S.M.: "Challenger" St. C83/62, 32"29'N:16°43'W, A 62, B 2; C83172, 32°30'N:16°43'W, A 27.

Central subtropical Atlantic (25°-400W) I.O.S.: "Discovery" St. 8265,32"01 'N:27°12'W, A I I; 8270, 32"OS'N:34°23'W, A 8; 8271, 31°S8'N: 39°02'W, A 2, B I; 10222 #1-4,6,9, 14-18, 33°N:30'W, A 368, B 15, L I I; 10228 #4-8,11,15,22- 26,28-30, 33°N: 31°30'W, A 123, B 7, L 417; 10232 #1-6.13-19, 33°0S'-32°18'N:31°38'-28°W, A 688, B 74, L 1049; 10233 #5-9,11. 12, 19,21-24,26-28, 32"N:31°30'W, A 180, B 6, L 160; 10241 #1-8.15,17, 33°IO'N:31°S0'W, A 860, B 5; 10243 #4-6, 33°N:31°30'W, A 9; 10244 #3, 4, 32°S0'N: 31°14'W, A 6; 10245 #3, 32°26'N:30046'W, A 3; 10376 #25-27, 30-33, 37, 38, 33°20'N:33°30'W, A 516; 10378 #11. 13, 16,22-26, 32°20'N:29°50'W, A 78; 10379 #11. 12, 14-16, 18,20,21,29,39, 3soN:33°W, A 80; 10380 #7. 8, 10, 12, 26, 28, 29, 32, 300N:33°S0'W, A 5, B 17, L 6; 10382 #2-4, Il-13, 18. 32°35"N:32°W, A I 13, L I. 1.T.Z.: "Tydeman" I.T.Z. Project lOlA St. 17 #1, 41°01'N:3so3I'W, A 2; 20 #3,10,12, 3so16'N: 31"36'W, A 48; 21 #10, 33°26'N:30038'W, A II; 22 #6, 7, 9, 32°N:29°S3'W, A 66, B 10; 24 #1-3. 29°49'N:29°57'W, A 6, B I; 25 #1. 3, 9, 28°30'N:29°S8'W, B 9; 26 #11. 24°48'N:30008'W, B 8; 27 #2. 10,23. 24°48'N:28°41'W, B 17; 46 #6, 7, 35"07'N:31°21'W, A 61; 48 #5, 7, 34°12'N:31"13'W, A 4; 49 #6, 31°44'N:29°3S'W, A 3; 50 #2,13, 30013'N:29°43'W, A I, B 3; 52 #1, 24°S0'N:30oW, B 3; 84 #31, 35°IO'N:31"30'W, A 3; 85 #14, 33°31'N:30012'W, A I; 87 #11. 29°59'N:29°33'W, B 3; 88 #5, 28°30'N:29°51'W, B I; 89 #3, 24°50'N:29°55'W, B 18; 90 #16, 24°55'N:28°40'W, B 4.

Western subtropical Atlantic (W of 400W)

I.O.S.: "Discovery" St. 8272, 31°58'N:43°37'W, A 8; 8274, 31°58'N:47°18'W, A 7, B I; 8275, 32°01'N:50033'W, A 12, B I; 8276, 31°56'N:54"OS'W, A 18; 8277, 32°05'N:57°40'W, A 9; 8279, 32°22'N:60024'W, A 3; 8281 #19, 31°54'N:63°38'W, A 146.

Eastern tropical Atlantic (23°-18/N)

I.O.s.: "Discovery" St. 7056, 22°36'N:20002'W, A 2; 7059, 22°18'N:20041'W, A I, L I; 7060, 20038'N:22°32'W, A 12; 7061, 2001S'N:22°49'W, A 7; 7064, 19°5S'N:23°27'W, AS; 7066, 19°18'N: 24°27'W, A 3; 7068, 19°03'N:24°59'W, A 6; 7070, 18°50'N:25°13'W, A 4, L I; 7089 #26, 17°S2'N: 25°25'W, A 20, B I.

Eastern equatorial Atlantic

I.O.s. "Discovery" St. 6662 #2,3, I ION:200W,A 7; 8556 #2,3, 00020'S:22"05'W, A 4, L 10; 8559 #4, 00°1 S'S:22°44'W, A 9; 8560 #1, 00006'N:22°44'W, A 3; 8562 #8, 00034'S:2 1052'W, A 3; 8563 #6, 03°02'N:23"06'W, A 16; 10523 #12, 13, 18, 19, 05°S:00025'E, A 7.