Leptocephalus Larvae of the Tribe Sphagebranchini (Pisces, Ophichthidae) in the Western North Atlantic

BULLETIN OF MARINE SCIENCE, 32(1): 220-236, 1982

LEPTOCEPHALUS LARVAE OF THE TRIBE SPHAGEBRANCHINI (PISCES, OPHICHTHIDAE) IN THE WESTERN NORTH ATLANTIC

Mark M. Leiby

ABSTRACT Larvae of Apterichtus ansp, A, kendalli, Ichthyapus ophioneus, a problematical specimen tentatively identified as Microrhynchus (sensu Blache and Bauchot, 1972) sp. and Sticto- rhinus potamius are described. A. ansp, A. kendalli, I. ophioneus and Microrhynchus sp. are characterized by having the dorsal fin confined to the tail-tip and by reduction in gill arch development. S. potamius is characterized by its highly developed pigmentation and by its dorsal fin origin above the anus. An explanation for the difficulties encountered in determining dorsal fin origin in ophichthid larvae is given.

The ophichthid tribe Sphagebranchini (sensu McCosker, 1977) comprises ]2 nominal species in the Atlantic and Mediterranean. Blache (1977) described five series of larvae from the eastern Atlantic which he identified as Microrhynchus sp. aff. foresti, Apterichtus caecus, Verma kendaLli, V. monodi and Verma sp. Fahay and Obenchain (1978) identified two forms of larvae from the western Atlantic as Apterichtus (=Verma) kendalli and A. ansp. Recently, Leiby (in press) questioned these authors' identifications and descriptions of Verma monodi, Verma sp., Apterichtus (=Verma) kendalli, and A. ansp. This paper provides definitive larval descriptions of A. ansp, A. kendalli, Ichth- yapus ophioneus, a problematical specimen tentatively identified as Microrhyn- chus (sensu Blache and Bauchot, 1972) sp., and Stictorhinus potamius. It also provides an explanation for the difficulties occasionally encountered in determining dorsal-fin origin in ophichthid larvae.

METHODS

Measurements were made to the nearest 0.1 mm using an optical micrometer in a dissecting microscope. All counts, measurements, and growth stages are as defined in Leiby (1979a, b). At least one larva of each species was stained for bone and cartilage following Dingerkus and Uhler (1977) and dissected for osteological study. Drawings were made using a camera lucida on a dissecting microscope. Data on adult A. ansp, A. kendalli, and I. ophioneus were obtained from cleared and stained specimens, from the literature and from x-rays provided by Dr. James E. Bohlke, Academy of Natural Sciences, Philadelphia. Data on Microrhynchus foresti were obtained from the literature. Data on S. potamius were obtained from the literature and from x-rays provided by Eugenia B. Bohlke. Collection locations for the species examined are shown in Figure I. Institutional abbreviations used in this study are: Harvard University, Museum of Comparative Zoology, Cambridge, Massachusetts (MCZ); Marine Biomedical Institute, Galveston, Texas (MBI); Florida Department of Natural Resources, Marine Research Laboratory, St. Petersburg, Florida (FSBC); National Marine Fisheries Service, Northeast Fisheries Center, Highlands, New Jersey (NMFS-NFC); South Carolina Wildlife and Marine Resources Department, Charleston, South Car- olina (SCMRD); Rosenstiel School of Marine and Atmospheric Science, Miami, Florida (UMML); University of Rhode Island, Kingston, Rhode Island (URI).

Apterichtus ansp (Bohlke) Figures 2, 4, 5; Table 3 ldentification.-An advanced metamorphic larva in a series of 28 specimens had two temporal pores (TP ]-2) and four preoperculomandibular pores (POP ]-4) 220 LEIBY: LARVAL SPHAGEBRANCHINI 221

•• :Apterichtus ansp

o :Apterichtus kendalli 0: Ichlhyapus ophioneus .: ?Mlcrorhynchus sp.

• : Stictorhinus potamlU5

C>-. 0 ,~,

o •• o

Figure I. Distribution of larval Microrhynchus sp., Stictorhinus potamius, Apterichtus ansp, A. kendalli and Ichthyapus ophioneus. in the cephalic lateralis system. This condition is found only in the tribe Sphag- ebranchini. The specimen was cleared and stained; the hydroid arch had ]6 branchiostegals; the gill arches (Fig. 2A) lacked basibranchials two and three (B 2-3), had basibranchial four (B 4) so weakly developed that it would be reduced or lost by the time metamorphosis was complete, and had a small ceratobranchial five (C 5) that would be reduced or absent in adults. Apterichtus is the only Atlantic sphagebranchin genus known to lack B 2-3, to have B 4 and C 5 either reduced or absent, and to have so few branchiostega]s. Comparison of total and nephric myomere counts of the larvae with total and precaudal counts of the six nomina] adult Apterichtus species in the Atlantic eliminated all but A. ansp (a western Atlantic species) and A. gracilis (an eastern Atlantic species). The presence of small (9.9 mm TL) larvae in the South Atlantic Bight indicates a recent spawning in the western North Atlantic. Consequently, the series of larvae can only be A. ansp.

1 mm 1m'" Figure 2. (Left) A, Gill arches of Apterichrus ansp from a 57.0-mm TL euryodontic specimen; B, Caudal skeleton of same specimen. Figure 3. (Right) A, Gill arches of Aptericlzrus kendalli from a 76.9-mm TL early metamorphic specimen; B, Caudal skeleton of same specimen. 222 BULLETIN OF MARINE SCIENCE, VOL. 32, NO. 1.1982

Figure 4. Apterichtus ansp, engyodontic stage. A, Leptocephalus 9.9 mm TL; B, Head of same specimen.

General Morphology.-Twenty-eight larvae examined, 9.9-70.2 mm total length (TL). Body relatively elongate, much compressed, clear. Dorsal fin confined to tail-tip until late metamorphosis when all fins resorbed. Total myomeres 129-136; nephric myomeres 63-67; preanal myomeres 65-70, anus migrates anteriorly during metamorphosis; predorsal myomeres 114-125 in late euryodontic and early metamorphic specimens; predorsal myomeres cannot be determined in engyodontic or early euryodontic larvae. Branchiostegals 15-16. Generally nine much- reduced gut loops or swellings, often differentiable from preservation artifacts only by chromatophore patch beneath nephric duct on swelling (Table I); two usually distinct loops along esophagus, first at anterior end of liver, second at posterior end of liver; gut expands posterior to gall bladder and liver. Nephros terminates one to three myomeres anterior to anus. Relative preanal length (PAL) and head length (HL) decrease with growth of specimen due to differential growth in tail region (Table 2). Preanal myomere number remains constant. Pigmentation.-Pigment in formalin-preserved specimens inconspicuous (Figs. 4,5). Weak pigment on anterior half of upper and lower jaws near base of teeth; on lower jaw lateral to juncture of quadrate and Meckel's cartilage; on cheek lateral to hyomandibula. A variable number of chromatophores in body wall lateral to heart. One or more small chromatophores at midline on each myoseptum starting as far forward as myomere six, frequently uniting to form streak of pigment on myosepta. Weak pigment on dorsal surface of esophagus near pectoral- fin base. Five to nine irregular pigment patches along dorsal surface of gut, first two mark anterior and posterior lobes of liver, remaining three to seven patches mark gut swellings; number of pigment patches on gut increases from hatching to euryodontic stage. Small, scattered patches of pigment in body wall ventral to gut. Three to five faint, irregular subcutaneous pigment patches on tail just ventral to aorta near postanal myomeres 8-]2, 17-23, 25-35, 38-46, 49-57, number of patches increase from hatching, generally becoming five by early euryodontic stage. A single, weak chromatophore patch on ventral surface of each anal-fin pterygiophore.

Material Examined.-Uncatalogued specimens from: NMFS-NFC (13 specimens, 20.2-70.7 mm TL); SCMRD (12, 9.9-29.5); UMML (2, 51.1-57.0); URI (I, 70.2). Engyodontic specimens collected in South Atlantic Bight; metamorphic specimens taken otT Grand Bahama Isle, and otT South Carolina. LEIBY: LARVAL SPHAGEBRANCHINI 223

Table I. Location of gut loops relative to myomere number in four species of sphagebranchin larvae. Values represent maximum range of occurrence observed for each gut loop. Loops are generally two to five myomeres long. (I = frequently low or absent; 2 = occasionally low but always present; 3 = occasionally low or absent)

Gut Loops

Species #1 #2 #3 #4 #5 #6 #7 #8 #9

A. ansp 10-16 18-23 24-28' 29-351 36-41' 41-46' 50-54' 56-62' 63-701 A. kenda/li 10-]4 18-25 27-30' 31-37 38-42t 44-5()2 52-583 60-66 67-74 I. ophioneus 9-12 17-21 26-30 35-41 47-54 S. potamius 10-13 18-23 26-29 33-38 42-45 49-53 57-62 67-73 71-76

Apterichtus kendalli (Gilbert) Figures 3, 6, 7; Table 3 ldentification.-Late euryodontic and early metamorphic larvae in a series of 24 specimens clearly had the dorsal fin confined to the tail-tip, indicating that the larvae were finless sphagebranchins. The gill arches (Fig. 3A) of a cleared and stained specimen lacked B 2-3 and had B 4 and C 5 so weakly developed that they would be reduced or absent in adults. The hyoid arch had 15branchiostegals. This combination of characters indicated that the series belonged to Apterichtus. The cephalic lateralis system was not fully developed in any of my specimens. Nevertheless, there were clearly four supraorbital pores, SO 1-4 (not including the ethmoidal pore or the median pore in the frontal commissure). The number and condition of the ossicles showed that TP 2 was absent, that POP 1-3 were present and that POP 4 was probably absent. Comparison of the cephalic lateralis system, total myomeres, and nephric myomeres of the larvae with the cephalic lateralis system, total vertebrae, and precaudal vertebrae of the known adult Atlantic Apterichtus spp. eliminated all but A. kendalli. General Morphology.-Twenty-four larvae examined, 5.8-90.3 mm TL. Body relatively elongate, much compressed, clear. Dorsal fin confined to tail-tip until late metamorphosis when all fins resorbed. Total myomeres 137-148; nephric myomeres 67-73; preanal myomeres 69-74, anus migrates anteriorly during meta-

Table 2. Body proportions in five species of sphagebranchin larvae (TL = total length; PAL = preanal length; HL = head length)

Developmental Size Range No. of Species Stage (TLmm) Larvae PAL%TL HL%TL HL%PAL

A. ansp Engyodontic 9.9-19.0 9 68.7-73.6 10.9-14.3 14.9-20.9 Euryodontic 20.2-70.2 16 54.0-73.3 5.6-10.9 9.8-14.9 Metamorphic 51±-71± 2 ? ? ? A. kendalli Engyodontic 5.8-18.5 8 70.3-75.9 10.3-]6.2 14.5-21.4 Euryodontic 26.7-90.3 14 57.3-63.8 5.1-8.2 8.8-12.8 Metamorphic* 76.9-85± 2 54.0 5.6 \0.4 I. ophioneus Engyodontic 8.2 1 64.6 14.9 23.0 Euryodontic 28.5-83.7 14 40.2-53.3 4.3-7.7 \0.6-14.5 Metamorphict 49±-71.5 3 40.5-40.7 5.4-5.5 13.0-13.5 Microrhynchus sp. Euryodontic 85.2 I 68.4 4.7 6.9 S. potamius Euryodontic 25.0-83.2 9 60.4-71.4 5.3-8.8 8.7-12.3

• Percentages given for smallest and most completely transformed specimen. large~t specimen too badly deformed to measure accurately. t Percentages given are for two specimens 69.6 and 71.5 mm TL, smallest specimen too badly deformed to measure accurately. 224 BULLETIN OF MARINE SCIENCE, VOL. 32, NO. I, 1982

'0\))

/!D

1mm lmm Figure 5. Apterichtus ansp. A, Euryodontic stage specimen 57.0 mm TL; B, Head of same specimen; C, Head of metamorphic stage specimen 51.1 mm TL. morphosis; predorsal myomeres 121-135 in late euryodontic and early metamorphic specimens; predorsal myomeres cannot be determined in engyodontic or early euryodontic larvae. Branchiostegals 15-16. Six to nine weak to moderate gut loops (Table 1); two distinct loops along esophagus, first at anterior end of liver, second at posterior end of liver; gut expands posterior to gall bladder and liver. Nephros terminates one to three myomeres anterior to anus. Relative PAL and HL decrease with growth of specimen due to differential growth in tail region. Preanal myomere number remains constant. Pigmentation.-Pigment in formalin-preserved specimens conspicuous (Figs. 6, 7), more like pigment of A. caeclis (Blache, 1977, fig. 95) than A. ansp. Amount of pigment increases with growth. Pigment on upper jaw similar to that of A.

Figure 6. Apterichlus kef/da/li, euryodontic stage. A, Leptocephalus 59.2 mm TL; B, Leptocephalus 18.5 mm TL; C, Head of specimen 57.3 mm TL; D, Head of specimen ]8.5 mm TL. LEIBY: LARVAL SPHAGEBRANCHINI 225

Figure 7. Apterichtus kendalli, metamorphic stage. A, Leptocephalus 78.2 mm TL; B, Head of same specimen. ansp. Little or no pigment on lower jaw or cheek until late euryodontic, then like A. ansp. A variable number of stellate chromatophores in body wall lateral to heart. In engyodontic and euryodontic larvae, groups of often stellate chromatophores lateral to notochord every 6-10 myomeres; this pigment associated with, but not limited to, myosepta. Myosepta between groups of chromatophores not pigmented, unlike larval A. caecus which has both stellate chromatophores in groups, and streaks of pigment on most myosepta. Irregular pigment patches along dorsal surface of gut marking each gut loop. In engyodontic and euryodontic larvae, groups of occasionally stellate chromatophores in body wall lateral to most gut loops. Body wall pigment increases with growth. By mid-euryodontic stage, groups of occasionally stellate chromatophores in body wall ventro-lateral to gut from midway between heart and anterior end of liver to anus. Three to five irregular subcutaneous patches of pigment on tail just ventral to aorta near postanal myomeres 10-15, 21-25, 27-33, 38~3, 45-53; these patches often obscured by groups of stellate chromatophores in body wall lateral to them; number of subcutaneous patches increases from hatching, generally becoming five by early euryodontic stage. In euryodontic stage, ventral margin on tail marked every 7-12 myomeres by saddle-shaped groups of often stellate chromatophores. Ventral surface of anal fin pterygiophores unpigmented except in area of saddle- shaped pigment patches. Pigmentation in metamorphic specimens extensive, giv- ing peppered appearance to entire animal (Fig. 7).

Material Examined.-Uncatalogued specimens from: MBI (9, 18.5-59.2); UMML (2, 29.7-60.7); URI (4,62.2-90.3). Catalogued specimens: FSBC 11553L (2, 17.2-17.6), FSBC I 1554L (1,55.0), FSBC I 1555L (I, 76.9), FSBC I 1556L (5, 5.8-14.0). Engyodontic specimens taken throughout the Gulf of Mexico and on east coast of Florida. Metamorphic specimens taken in northeast Gulf of Mexico and Ocean Acre, Bermuda.

Ichthyapus ophioneus (Evermann and Marsh) Figures 8, 10, ] 1; Table 3 Identification.-An advanced metamorphic larva in a series of ]8 had SO ]~, TP 1-2, and POP ]~ in the cephalic lateralis system. Euryodontic and metamorphic specimens clearly had the dorsal fin confined to the tail-tip. These con- ditions occur only in finless sphagebranchins. A cleared and stained specimen lacked B 2~, had a small C 5 that probably would be reduced or absent in the 226 BULLETIN OF MARINE SCIENCE, VOL. 32, NO. I, 1982

lmM

'mm ,mm

Figure 8. (Left) A, Gill arches of lchthyapus ophioneus from a 48.6-mm TL metamorphic specimen; B, Caudal skeleton of same specimen. Figure 9. (Right) A, Gill arches of Microrhynchus sp. from an 85.2-mm TL euryodontic stage specimen; B, Caudal skeleton of same specimen. adult (Fig. 8A), and had 24 branchiostegals. Ichthyapus is the only finless Atlantic sphagebranchin genus known to lack B 2-4, to have SO 1-4, TP 1-2, POP 1-4, and to have 24 or more branchiostegals. The only species of Ichthyapus in the Atlantic is I. ophioneus. Comparison of total and nephric myomere counts of the larvae with total and precaudal vertebral counts of adults confirmed the identification of the larvae as I. ophioneus. General Morphology.-Eighteen larvae examined, 8.2-83.7 mm TL. Body relatively elongate, much compressed and clear. Dorsal fin restricted to tail-tip until late metamorphosis when all fins resorbed. Total myomeres 130-139; nephric myomeres 49-53; preanal myomeres 50-54, anus migrates anteriorly during metamorphosis; predorsal myomeres ] 17-130; predorsal myomeres cannot be determined in engyodontic or early euryodontic larvae. Branchiostegals 23-26. Five moderate gut loops; first at anterior end of liver, second at posterior end of liver; gut expands posterior to gall bladder and liver. Relative PAL and HL decrease with growth of specimen due to differential growth in tail region. Preanal myomere number remains constant.

lmm

lmm Figure 10. lchthyapus ophioneus, engyodontic stage. A, Leptocephalus 8.2 mm TL; B, Head of same specimen. LEIBY: LARVAL SPHAGEBRANCHINI 227

lmm

lmm 1mm I Figure II. Ichthyapus ophioneus. A, Euryodontic stage specimen 28.5 mm TL; B, Head of same specimen; C, Euryodontic stage specimen 71.7 mm TL; D, Head of same specimen; E, Head of metamorphic stage specimen 69.9 mm TL

Pigmentation.-Pigment inconspicuous in formalin-preserved specimens (Figs. to, 11). Weak pigment on anterior half of upper and lower jaw near margin of lips and on side of head lateral to medulla. A variable number of chromatophores in body wall lateral to heart. Streak of pigment on nearly every myoseptum starting as far forward as myomere five. Five to eight irregular pigment patches along dorsal surface of gut; five patches accentuate gut loops; three, when present, lie between gut loops. Little or no body wall pigment lateral or ventral to gut. Three irregular subcutaneous pigment patches on tail just ventral to aorta near postanal myomeres 10-13, 28-34, 42-46. A single, weak chromatophore patch on ventral surface of each anal fin pterygiophore.

Material Examined.-Uncatalogued specimens from: MBI (4, 8.2-39.8); UMML (8, 48.6-83.7); URI (2,65.1-66.4). Catalogued specimens: FSBC 11558L (I, 73.0); FSBC I 1559L (I, 71.7); FSBC I 1560L (I, 39.7); FSBC 11561L (I, 72.1). One engyodontic specimen taken between Yucatan Peninsula and Cozumel Island. Metamorphic specimens taken from Bahama Islands.

Microrhynchus (sensu Blache and Bauchot, 1972) sp. Figures 9, 12; Table 3 Identijication.-Assignment of this 85.2 mm TL specimen to the tribe Sphage- branchini (sensu McCosker, 1977), despite its high nephric myomere to total 228 BULLETIN OF MARINE SCIENCE, VOL. 32, NO. J, 1982

1mm

Figure 12. Microrhynchus sp., euryodontic stage. A, Leptocephalus 85.2 mm TL; B, Head of same specimen. myomere ratio, rests on the condition of the dorsal fin and on the elimination of other possibilities. The dorsal fin in this late euryodontic specimen differs from that of other finless sphagebranchin larvae (see Discussion); nevertheless, the lack of even rudimentary dorsal pterygiophores anterior to myomere 200 indicates that the specimen would be finless as an adult. The only known finless ophichthids are all sphagebranchins. The only two non-sphagebranchin genera in the Atlantic known to contain species with total and precaudal vertebral ranges and proportions comparable to this specimen are Bascanichthys and Callechelys. Bascan- ichthys and Callechelys larvae have dorsal pterygiophores anterior to the anus before they reach the stage of development of this specimen. The gill arches of the specimen (Fig. 9A) are more similar to those of larval Apterichtus and [chthyapus (Figs. 2A, 3A, 8A) than they are to larval Bascanichthys (Leiby, in press) or Callechelys (pers. obs.). The heads and chondrocrania of larval Bas- canichthys and Callechelys are shorter and deeper than the head and chondro- cranium of this specimen (pers. obs.). The extremely low gut looping of this specimen (Fig. l2A) is common in Bascanichthys but unknown in Callechelys. While none of these characters conclusively eliminate all other tribes from con- sideration, all the characters taken together indicate that the specimen is the larva of a finless eel in the tribe Sphagebranchini. Identifying this sphagebranchin larva to genus and species is problematical. The cephalic lateralis system is not sufficiently developed to provide any help. Nevertheless, because this specimen has a rudimentary B 2, lacks a rudimentary B 4, has 26 branchiostegals, has a dorsal fin development which differs from that of Apterichtus (see Discussion), and because its caudal osteology is different from Apterichtus spp. (Figs. 2B, 3B), it clearly cannot be an Apterichtus (sensu McCosker, 1977). The 26 branchiostegals could ally it with Ichthyapus. However, the caudal osteology (Figs. 8B, 9B) and dorsal fin formation of this specimen (see Discussion) are different from that of larval I. ophioneus. The seven world- wide nominal species of Ichthyapus all have 147 or fewer total vertebrae and fewer precaudal than caudal vertebrae. This larval specimen has over 200 total myomeres and substantially more nephric than postnephric myomeres. The specimen cannot be an Ichthyapus (sensu McCosker, 1977). LEIBY: LARVAL SPHAGEBRANCHINI 229

The only known sphagebranchin which has total and precaudal vertebral counts (187,134) approximating the total and nephric counts of my specimen (217, 138) is the eastern Atlantic Sphagebranchus foresti (Cadenat and Roux, 1964), which Blache and Bauchot (1972) used as the type of a new genus, Microrhynchus. There is no information available on gill arch condition, caudal osteology, or number of branchiostegals (although the drawing of the holotype shows at least 21 branchiostegals) by which my specimen can be reliably associated with the nominal genus Microrhynchus (sensu Blache and Bauchot, 1972). However, Blache (1977) described four specimens with a total myomere range of 191-195 and a nephric myomere range of 131-135 which he identified as Microrhynchus sp. aff. foresti. The similarities (head shape, gut morphology, nephros morphology, head pigment, gut pigment and body wall pigment lateral to the notochord) between his specimen and mine indicate that our specimens are probably in the same genus. The much higher total myomere count of my specimen (at least 22 myomeres more than any of his and 30 more than the holotype of M. foresti) and the differences in pigmentation between his specimens and mine (his specimens, as illustrated, lack body wall pigment on the lower arm of the myomeres between notochord and gut, and on the dorsal margin of the body) make it impossible to state with certainty that we are dealing with the same species. Resolution of this problem will have to wait the discovery and comparison of more specimens of this type on both sides of the Atlantic. McCosker (1977) was unable to examine S. foresti, the type of the genus Mi- crorhynchus (sensu Blache and Bauchot, 1972), but concluded that their sketchy description of external morphology did not provide characters which would allow its generic separation from Apterichtus or possibly Ichthyapus. He also noted that if the genus is valid, it would require a substitute name because Microrhyn- chus is preoccupied. Since my specimen, and the larvae described by Blache (1977) as Microrhynchus sp. aff. foresti, are clearly different from larvae of Ap- terichtus and Ichthyapus, it is apparent that there is another taxon, of either generic or subgeneric rank, in the tribe Sphagebranchini (sensu McCosker, 1977) in the Atlantic. Resolution of the problem will have to await a re-examination of the holotype of S. foresti and an osteological comparison of S. foresti with Ap- terichtus and Ichthyapus. General Morphology.-One specimen examined, 85.2 mm TL. Body elongate, much compressed, clear. Dorsal fin confined to tail-tip. Total myomeres 217; nephric myomeres 138; preanal myomeres 138; predorsal myomeres 200. Bran- chiostegals 26. Gut loops in this specimen so reduced and gut pigmentation so extensive that number of gut loops cannot be determined. Anterior lobe of liver under myomeres 11-13, posterior lobe of liver under myomeres 22-24. Nephros terminates over, or slightly posterior to, anus. Specimen examined, late euryodontic. Pigmentation.-Pigment in formalin-preserved specimen conspicuous (Fig. 12). Head pigment at base of teeth on anterior half of upper jaw; at base of first two teeth on lower jaw; lateral to juncture of quadrate and Meckel's cartilage; on side of head lateral to medulla. Body wall pigment complex. Dorsal edge of body marked by groups of chromatophores two to eight myomeres apart starting at myomere 25. Pigment lateral to notochord consists of dots or streaks of pigment on every third to eighth myoseptum and groups of stellate chromatophores on myomeres adjacent to myoseptum pigment. Pigment on myomeres between notochord and gut consisting of variable amounts of pigment on myosepta and myomeres; pigment occurs randomly at intervals of two to six myomeres from 230 BULLETIN OF MARINE SCIENCE, VOL. 32, NO. I, 1982 just ventral to notochord to ventral edge of myomeres. Ventral edge of body marked by groups of chromatophores ventrolateral to heart, esophagus, and along length of liver. Pigment on esophagus near base of pectoral fin. Numerous irregular pigment patches along dorsal surface of gut occurring at intervals of two to five myomeres. Three irregular, subcutaneous patches of pigment on tail just ventral to aorta at postanal myomeres 12, 28, 44; postanal subcutaneous spots partially obscured by body wall pigment lateral to them. Weak chromatophore patch on ventral surface of each anal pterygiophore; strong pigment on groups of four to ten pterygiophores spaced two to eight pterygiophores apart may give appearance of interrupted pigment at base of anal fin.

Material Examined.-MCZ 55464 (1, 85.2).

Stictorhinus potamius Bohlke and McCosker Figures 13, 14; Table 3 Identification.-Except for the supraorbital series which has three pores, the cephalic lateralis system in the most advanced specimen of the series is not sufficiently developed to positively establish it as a sphagebranchin. Consequent- ly, the identification of the series rests on the process of elimination. All genera of the tribe Callechelyini and all genera of the tribe Bascanichthyini except Dal- ophis can be eliminated by the ratio of nephric to total myomeres and the posterior position of the dorsal fin in these larvae (Fig. BA). All members of the tribe Sphagebranchini except Stictorhinus can be eliminated based on the condition of the gill arches (Fig. 14A), number of branchiostegals (24+), or the number of supraorbital pores. All members of the tribe Ophichthini except Pisodonophis can be eliminated based on the ratio of nephric to total myomeres, position of the dorsal fin, condition of the gill arches, and number of branchiostegals, or because the larvae of the genera are already known and they differ trenchantly from the larvae of this series. The only known Pisodonophis in the Atlantic, P. semicinctus, has more vertebrae (151-162) than these larvae (134-140). Only two nominal species of Dalophis, D. multidentatus and D. obtusirostris, have total vertebral counts similar to the total myomeres of these larvae. Nothing is known of the gill arches, branchiostegals, or number of precaudal vertebrae of either species of Dalophis. However, Blache and Bauchot' s (1972) description of lateral line pores in D. multidentatus indicates that it probably has fewer precaudal vertebrae than this larval series. D. obtusirostris is known only from the coasts of Senegal and Mauritania in Mrica; Stictorhinus is known only from Brazil in the western Atlantic. The presence of 25.0-29.0 mm TL larvae in the Straits of Florida makes it unlikely that these larvae can be D. obtusirostris. It is possible that these larvae are of an undescribed species of Pisodonophis or Dalophis in the western Atlantic, or that they belong to an undescribed genus. However, the close agreement between gill arch condition, number of branchiostegals, and number of total and nephric myomeres of the larvae with the same characteristics in adult S. potamius makes it likely that the larvae are those of S. potamius. Bohlke and McCosker (1975) indicate that S. potamius lacks C 5, but their illus- tration of the gill arches indicates a cartilaginous rudiment of C 5 at the anterior edge of the lower pharyngeal tooth plate. General Morphology.-Nine larvae examined, 25.0-83.2 mm TL. Body moder- ately elongate, much compressed, clear. Dorsal fin origin above anus. Total myomeres 134-140; nephric myomeres 71-75; preanal myomeres 72-76; predorsal r:nyomeres 71-78. Dorsal and anal fins migrate anteriorly during metamorphosis. LEIBY: LARVAL SPHAGEBRANCHINI 231

Figure 13. Stictorhinus potamius, euryodontic stage. A, Leptocephalus 48.3 mm TL; B, Lepto- cephalus 83.2 mm TL; C, Head of specimen 48.3 mm TL; D, Head of specimen 83.2 mm TL.

Branchiostegals not fully formed, only 24 discernable in most advanced specimen, but remaining developmental area has space for four to six more. Generally eight moderate gut loops with a ninth, lower, incomplete loop usually at end of gut lying very close to eighth loop (Fig. 13). First loop at anterior end of liver, second at posterior end of liver; gut expands posterior to gall bladder and liver. Nephros terminates one to three myomeres anterior to anus. Relative PAL and HL decrease with growth of specimen due to differential growth in tail region. Preanal myomere number remains constant. Pigmentation.-Pigment in formalin-preserved specimens pronounced (Fig. 13). Pigment on head consists of often stellate chromatophores on anterior half of upper jaw near base of teeth, on side of head lateral to medulla, and on top of head posterodorsal to hind-brain. Body wall pigmentation complex. Dorsal margin of body marked by saddle-shaped groups of stellate chromatophores three to eight myomeres apart. Pigment lateral to notochord consists of dots or dashes of pigment on every second to fourth myoseptum and groups of stellate chromatophores adjacent to a pigmented myoseptum on every third to sixth myomere. Ventral edge of body marked by irregularly shaped groups of stellate chromatophores ventrolateral to esophagus and liver and lateral to each gut loop, and by saddle-shaped groups of stellate chromatophores along ventral margin of tail. Stellate chromatophores on esophagus near base of pectoral fin. Irregular pigment patches on dorsal surface of gut at peak of each gut loop and midway between each gut loop. Five irregular, subcutaneous patches of pigment on tail just ventral to aorta at postanal myomeres 4-6, 13-17, 26-31, 37-41,48-53; postanal subcutaneous pigment patches partially obscured by body wall pigment lateral to them. Weak chromatophore patches on distal margin of each dorsal and anal 232 BULLETIN OF MARINE SCIENCE, VOL. 32, NO. I, 1982

Figure 14. (Left) A, Gill arches of Stictorhinus patamius from an 83.2-mm TL euryodontic stage specimen; B, Caudal skeleton of same specimen. Figure 15, (Right) A, Anteriormost point of dorsal fin development in 78.4 mm TL euryondontic stage Ophichthus gamesi; left lateral view (myomeres 66-69); B, Dorsal view same specimen, same myomeres; C, Muscle striations in dorsal margin of 84.7-mm TL metamorphic A. kendal/i; left lateral view; myomeres 34-38; D, Dorsal view same specimen, same myomeres; E, Muscle striations and dorsal thickening in same specimen; left ]ateral view; myomeres 121-]25; F, Dorsal view same specimen. same myomeres. pterygiophore associated with saddle-shaped group of chromatophores; occasionally a few anal pterygiophores between saddle-shaped pigment groups also weakly pigmented.

Material Examined.-Uncatalogued specimens from: MBI (3, 29.0-51.1); UMML (I, 83.2). Cata- logued specimens from: FSBC 11557L (1,25.0); MCZ 55465 (1,81.8); MCZ 55466 (3, 34.1-79.4). No engyodontic or metamorphic specimens examined.

DISCUSSION All ophichthid larvae, including those which are finless as adults, develop median fin pterygiophores and actinotrichia. During metamorphosis, the finless eels resorb median fin pterygiophores and actinotrichia. Dorsal fin origin in all larval western Atlantic Ophichthinae is posterior to its adult position, but there is a correlation between dorsal fin origin in larvae and adults which can be useful in identifying larvae (Leiby, in press). Consequently, it is necessary to be able to accurately determine dorsal fin origin in larvae, a sometimes difficult task. Engyodontic ophichthid larvae have a diaphanous median fin-fold. Ventrally, its anteriormost point is the anus. Dorsally, its anteriormost point is variable depending on species. By the beginning of the euryodontic stage, this fin-fold is being resorbed and a dense gathering of cells is forming in which the pterygiophores will develop. The dense gathering of cells is first noticeable as an undif- ferentiated thickening in the dorsal and ventral margins of the body. This thickening reaches its anteriormost point and is generally noticeable in well preserved specimens between 30 and 60 mm TL (depending on species). In most species, other than the finless sphagebranchins, the anteriormost point of the thickening is also the anteriormost point of dorsal pterygiophore development and can be used to determine dorsal origin even before dorsal pterygiophore formation is complete. Caution must be used in determining dorsal origin in this way, however, because in specimens between 20 and 40 mm TL an erroneous reading can be caused by a receding fin-fold, a dorsal thickening which has not reached its anteriormost point, or a weakly developed dorsal thickening which is difficult to see. Dorsal pterygiophores develop from posterior to anterior and, in most species other than the finless sphagebranchins, the adult number is formed before meta- LEIBY: LARVAL SPHAGEBRANCHINI 233

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Muscle striations and a definite dorsal thickening are formed to myomere six, but even rudimentary pterygiophores are not forming anterior to myomere 200. All the Callechelyini, Bascanichthyini, Ophichthini, and finned Sphagebranchini (S. potamius) larvae I have examined which have reached the stage of development of this problematical specimen have dorsal pterygiophores and discrete muscle bundles forming to the anterior tip of the dorsal thickening. This specimen has retained more of the larval dorsal fin formation than the other two genera and is, consequently, the most difficult to identify as the larva of a finless sphagebranchin. Nevertheless, lack of dorsal pterygiophore development anterior to myomere 200 in a specimen of such an advanced state of development clearly demon- strates that it is the larva of a finless sphagebranchin. Blache (1977) described, illustrated and identified four larvae as Pisodonophis cruentifer. His specimens differ trenchantly from P. cruentifer larvae (Fahay and Obenchain, 1978; pers. obs.). Both Blache's larvae and Ophichthus cruentifer (=Pisodonophis cruentifer) (McCosker, 1977; Leiby, in press) larvae have nine gut loops; have total, nephric, and preanal myomere counts which overlap; and are highly pigmented. However, Blache's larvae have the nephros terminating on the last gut loop, one to three myomeres anterior to the anus. O. cruentifer larvae have the nephros terminating on the next to last gut loop, five to nine myomeres anterior to the anus. Dorsal fin origin of Blache's specimens is over the last gut loop, or over the anus, at myomeres 63-72. Dorsal fin origin in O. cruentifer larvae is over gut loop six to seven, at myomeres 44-57. Blache's larvae have pigment lateral to the medulla; O. cruentifer larvae do not. Clearly B1ache's larvae cannot be O. cruentifer. External gut and nephros morphology, dorsal fin origin, pigmentation, and body form of Blache's (1977) larvae agree well with Stictorhinus potamius larvae (Fig. 13). B1ache's P. cruentifer larvae are probably the larvae of an undescribed finned sphagebranchin closely related to S. potamius.

ACKNOWLEDGMENTS

W. L. Fink (MCZ), D. G. Smith (MBI), M. P. Fahay (NMFS-NFC), C. A. Barans (SCMRD), C. R. Robins (UMML), and W. H. Krueger (URI) loaned me specimens used in this study. I am grateful. I thank K. Peters (MRL) and G. Bruger (MRL) for their comments on this manuscript. I especially thank my wife J. Leiby for her encouragement, patient understanding and help during this study.

LITERATURE CITED

Blache, J. 1977. Leptocephales des Poissons anguilliformes dans la zone sud du Golfe de Guinee. O.R.S.T.O.M., Faune Tropicale 20. 381 pp. --, and M. L. Bauchot. 1972. Contribution a la connaissance des poissons anguilliformes de la cote occidentale d'Afrique. Troisieme note: les genres Verma, Apterichtus, lchthyapus, Heme- rorhinus, Caecu/a, Dalophis avec la description de deux genres nouveaus (Fam. des Ophich- thidae). Bull. Inst. Fondam Afr. Noire, Ser. A 33: 692-773. Bohlke, J. E., and J. E. McCosker. 1975. The status of the ophichthid eel genera Caecula Vahl and Sphagebranchus Bloch, and the description of a new genus and species from fresh waters in Brazil. Proc. Acad. Nat. Sci. Philad. 127: 1-11. Cadenat, J., and Ch. Roux. 1964. Resultats scientifiques des campagnes de la "Calypso": lIes du Cap-Vert; 3. Poissons Teleosteens. AnnIs. Inst. Oceanogr. Monaco 41: 81-102. Dingerkus, G., and L. D. Uhler. 1977. Differential staining of bone and cartilage in cleared and stained fish using alcian blue to stain cartilage and enzymes for clearing fish. Stain Tech. 52(4): 229- 232. Fahay, M. P., and C. L. Obenchain. 1978. Leptocephali of the ophichthid genera Ahlia, Myrophis, Ophichthus, Pisodonophis, Callechelys, Letharchus, and Apterichtus on the Atlantic continental shelf of the United States. Bull. Mar. Sci. 28: 442-486. Leiby, M. M. I979a. Leptocephalus larvae of the eel family Ophichthidae. I. Ophichthus gomesi Castelnau. Bull. Mar. Sci. 29: 329-343. 236 BULLETIN OF MARINESCIENCE, VOL, 32, NO. I, 1982

I979b, Morphological development of the eel Myrophis punctatus (Ophichthidae) from hatching to metamorphosis with emphasis on the developing head skeleton, Bull. Mar, Sci. 29: 509-521, ---, In Press. Larval morphology of the eels Bascanichthys bascanium, B. scuticaris, Ophichthus melanoporus and O. ophis (Ophichthidae), with a discussion of larval identification methods. Bull. Mar. Sci. McCosker, J. E. 1977. The osteology, classification anp relationships of the eel family Ophichthidae. Proc. Calif. Acad. Sci. 4: 123 pp.

DATE ACCEPTED: May 13, ]980.

ADDRESS: Marine Research Laboratory, 100 Eighth A~enue, SE, St. Petersburg, Florida 33701.