Food and Prey Detection in Two Deep-Sea Cephalopods: Opisthoteuthis Agassizi and O

BULLETINOFMARINESCIENCE,49(1-2): 288-299,1991

FOOD AND PREY DETECTION IN TWO DEEP-SEA CEPHALOPODS: OPISTHOTEUTHIS AGASSIZI AND O. VOSSI (OCTOPODA: CIRRATA)

Roger Villanueva and Angel Guerra

ABSTRACT The diet of Opisthoteuthis agassizi and O. vossi in the southeast Atlantic was studied from 171 and 121 individuals respectively. Small epibenthic and supra benthic crustaceans and polychaetes are the most frequent prey items in both species, suggesting that they feed on suprabenthic and epib<:nthic material. Diel analysis of feeding by O. agassizi at 490 m and O. vossi at 836 m depth demonstrated a pattern of continuous feeding. Relationships oftotal body length and beak measurements to total weight were also studied. The ultrastructure of sucker and cirri are described for both species and their relationship with prey detection mechanisms is discussed.

The cirrate octopods represent the oldest evolutionary lineage of octopods, adapted to the deep-sea environment, where they have been recorded at depths of up to 7,229 m (Voss, 1988a; Aldred et al., 1983). The trophic position of these octo pods in the benthopelagic ecosystem is still unknown. The aim of the present study was to provide some insight onto the feeding patterns of the cirrates, which live in an area where light intensity and temperature are characterized by their low levels and lack of drastic changes. Furthermore, sucker and cirrus ultrastructure was investigated with the aim of relating their morphology to prey detection and capture. Two Opisthoteuthis species with overlapping distributions in Na- mibian waters (SE Atlantic) were selected: O. agassizi and O. vossi. Opisthoteuthis agassizi Verrill, 1883 is distributed on both sides of the Atlantic: from the Caribbean Sea to north of Brazil (Voss, 1988b), from the south coast of Ireland to the north coast of Spain and the Mediterranean Sea and from the Gulf of Guinea to Namibian waters (Morales, 1959; Adam, 1962; Sanchez, 1988; Voss, 1988b). Depth of capture ranges between 452 m (present study) and 2,250 m (Verrill, 1885). Opisthoteuthis vossi Sanchez and Guerra, 1989 is a species that lives off Namibian waters at 900 m depth.

MATERIALS AND METHODS

Sample Collection. -A total of 186 individuals of O. agassizi and 124 of 0, vossi were collected in Namibian waters (Table I Fig. I). Specimens were found in 42 stations during the scientific surveys Benguela-XIII (July, 1988), Benguela-XIV (January, 1989), Benguela-XV (July, 1989), and Benguela- XVI (March, 1990) on board the research ship CHICHA- TouZA and during commercial surveys on board the Freezer Trawler HERMANOSTOUZA(March, 1989) and the Freezer Trawler ITXAS-LuR(April, 1989). Depth ranges varied from 452 to 823 m for O. agassizi and from 778 to 888 m for O. vossi. Samples were taken by means of bottom trawls. Abundances in individuals per square kilometer were obtained from knowledge of the trawling device area and trawling speeds. Two time periods were sampled to study feeding rhythms. O. agassizi was sampled at 25°43'S, 13°40'E, between 483 and 490 m depth, during a 32-h cycle. Seven samples were collected: from 0920-1250, 1355-1620, 1730-2030, 22 I5-{)120, 022Q-{)600, 0710-1055, and 1300-1700 hr., 28-29 March 1989. A total of79 specimens was collected. O. vossi was sampled at 23°52'S, 13°1'E, at depths between 829 and 836 m. Four samples were collected: from 1645-1845, 230Q-{)100, 050Q-{)700 and 0950-1150 hr., 2-3 March 1990. A total of 96 individuals was collected. Immediately after collection, dorsal mantle length (DML), total length (TL) and total weight (TW) were measured for all individuals and their sex recorded. Individuals were dissected and their stomachs stored in 70% ethyl alcohol for further analysis. Mandibles of selected individuals were also dissected and fixed in 70% ethyl alcohol for upper crest length (DC) and lower crest length (LC) measurement.

288 VILLANUEVA AND GUERRA: FEEDING ECOLOGY IN Op/STHOTEUTHIS 289

Table 1. Opistoteuthis agassizi and O. vossi. Material examined. DML and TL in mm, TW in g. (SD, standard deviation; n, number of specimens; DML, dorsal mantle length; TL, total length; TW, total weight)

o. agassizi o. vossi Mean SO N Range Mean SO N Range DMLmales 67.8 18.4 118 13-108 85.3 22.6 75 40-140 DMLfemales 59.1 10.9 64 32-85 68 14.7 48 34-101 DML all specimens 64.4 17 184 13-108 78.5 21.6 123 34-140 TL males 238.6 88.8 108 38-482 288.4 83 71 125-465 TL females 195 45.5 59 104-342 222.4 44.2 46 126-355 TL all specimens 221.6 79.9 169 38-482 262.4 77.3 117 125-465 TW males 840.2 1,109.6 112 4-5,400 907.2 765.2 76 75-3,050 TW females 400.9 289.3 63 29-1,650 362.3 236.7 48 72-1,300 TW all specimens 674.5 925.9 177 4-5,400 696.3 671.6 124 72-3,050

Samples of suckers and cirri were fixed in 5% formalin water for optical microscope analysis. For scanning electron microscope analysis samples of suckers and cirri were fixed for I h in 2% glutar- aldehyde in buffered phosphate solution, washed in the same buffered solution and postfixed in 1% OsO •. Sample Processing.-In the laboratory stomachs were dissected and their contents identified to the lowest taxonomic level possible. The reference papers of McLaughlin (1980), Barnard et a!. (1962), and Kensley (1978) were used for identification purposes. A subjective index of stomach fullness (SF!) was applied, from 0 (denoting empty stomach) to 4 (denoting distended). Samples of cirri were dehydrated in a series of ethanol and embedded in paraffin. Sections (6-8 /Lm) were obtained and stained with haematoxylin and eosin for optic microscope analysis. Electron microscope samples were critical point dried in CO2 and examined with a Hitachi S-5 70 scanning electron microscope at 15 Kv. Data Treatment. -Student's '-tests were applied to the slopes of the different curves estimates. Krus- kall-Wallis non-parametric analysis of variance was applied to the stomach-fullness results, and x2 to analyze the day-night abundances recorded.

REsULTS Length-weight Regressions.-A total of 105 males, 58 females and 2 non-sexed specimens of O. agassizi and 71 males and 46 females of O. vossi were examined. DML and TL were analyzed and TL was chosen over DML due to its best fitting with TW. Total length (TL) versus Total Weight (TW) regressions are presented in Figures 2 and 3. No significant differences were observed between males and females within species or between species (t-test, P > 0.05). In the O. agassizi regression equation: TW = 2·IQ-5·TL3·1, with a correlation coefficient ofr = 0.96 (sexes mixed). In the O. vossi regression equation: TW = 19·IQ-5·TU·7, with r = 0.93 (sexes mixed). Mandibular Growth. - In O. agassizi the size of mandibles varied between 5.1 and 20.8 mm UC length and between 4.1 and 15.6 mm LC length. Regression equations are: logUC = 0.46 + 0.22 'logTW, with r = 0.94, on a total number of specimens, N = 58 (Fig. 4); and logLC = 0.36 + 0.22 'logTW, with r = 0.99 and N = 58 (always sexes mixed). In O. vossi mandibles varied between 6.9 and 20.5 mm UC length and between 6.1 and 16.2 mm LC length. Regression equations are: logUC = 0.43 + 0.24 'logTW, with r = 0.87 and N = 115 (Fig. 5); and logLC = 0.38 + 0.23 'logTW, with r = 0.86 and N = 115 (sexes mixed). No significant differences were observed between species (t-test, P > 0.05). 290 BULLETIN OF MARINE SCIENCE, VOL. 49, NO. 1-2, 1991

• • I I • • I I I I • I I • , I '- 15-

Zambezl River

Limpopo River

35°

40· - 40·S

I I I I Itt I I I t I I I I I I I I I I I I • I • • • • 15· 20· 25° 30· 35·E Figure 1. Sampled area.

Food and Feeding. - The remains found in the stomachs included setae and mandibles of polychaetes, appendages, mandibles and carapace pieces of crustaceans, pieces of microgastropods and microbivalves, sand and foraminifers. Exuviae of the calanoid copepod :species Undinopsis sp., Oothrix sp. and Ateidopsis sp. were recorded in four stomachs. The fact that Opisthotheuthis species do not have radulae permitted the identification of abundant whole prey items. Prey categories identified for the two species are shown in Table 2. A total of 125 individuals of O. agassizi and 93 of 0. vossi had prey items in their stomachs. Benthic gammarid amphipods and polychaetes comprised the major prey categories in both species (Table 3). For both species a maximum of 6 prey categories was observed in a single stomach. An average of 1.9 and 2.0 prey categories per stomach were observed for O. agassizi and O. vossi respectively. Whole prey sizes per category ranged 1- 8 mm in Crustacea, 1--2.5 mm in Gastropoda and 1.5-2.3 mm in Bivalvia. The diet of males and females proved to be similar. No differences in the type offood prey were observed between daytime and nighttime samples. Although octopod weight was independent of prey categories; for both species, polychaetes were more abundant as prey in the stomachs of individuals larger than 500 g, while amphipods dominated in individuals below 500 g (Table 3). VILLANUEVA AND GUERRA: FEEDING ECOLOGY IN OPISTHOTEUTHIS 291

o 5 Q,~gassizi o -m ~ 4 o Males -.s:: ,--m CD 3 + Females ~ ('is 2 -0 •••• 1 +

200 400 Total Length (mm) Figure 2. O. agassizi. Relationship between total length and total weight.

Diel Variability.-No differences were observed between nighttime and daytime samples of the cycles performed with the fullness stomach index (Kruskall-Wallis, P> 0.05), suggesting a continuous feeding. Inferred densities of O. agassizi ranged 6-16 ind' kIn -2 in daytime samples and 18-23 ind' kIn -2 in nighttime samples. The difference was not significant (X2, P

3 o 0 Q.vossi o 2.6 m -~ 2.2 o -.s:: o Males -m 1.8 'i + Females 1.4 o ~ o CU 1 -0 o •••• 0.6

0.2

200 400 Total Length (mm) Figure 3. O. vossi. Relationship between totailength and total weight. 292 BULLETIN OF MARINE SCIENCE, VOL. 49, NO. 1-2, 1991

-E E 1.3 O.agassizi -J: 1.2 m -c 1.1 Q) ...J 1 U) -Q) .•.. 0.9 0 .•.. 0.8 Q) Q. 0.7 ::::)Q. m 0.6 0 ...J 1 2 3 Log Total Weight (g) Figure 4. O. agassizi. The length (logarithm) of the crest of the upper beak plotted against total weight (logarithm). The broken lines on either side represent ±2 Sy (standard error ofY estimate).

> 0.05). However, diel changes in catches of O. vossi were found to be statistically significant (x2, P < 0.05), ranged 202-337 ind·km-2 and 256-499 ind'km-2 in daytime and nighttime hours respectively. Suckers and Cirri Ultrastructure. - Unmodified suckers were of 2-3 mm in diameter in both species, and suckers of both species had a conspicuous peduncle

, -E , E 1.3 O.v()ssi -:S 1.2 m ,, ; 1.1 ,, :: 1 U) ~ 0.9 ," o ,, , ; 0.8 , , , ,, Q. , , Q. 0.7 , ::::) , " ,, mO.6 ,, , o ,, ...J , 123 Log Total Weight (g) Figure 5. O. vossi. The length (logarithm) of the crest of the upper beak plotted against total weight (logarithm). The broken limlS on either side represent ±2 Sy (standard error of Y estimate). VILLANUEVA AND GUERRA: FEEDING ECOLOGY IN OPlSTHOTEUTH/S 293

Table 2. Food items identified from the stomachs of Opisthofetuhis agassizi and O. vossi

Food category O. agassizi o. voss; Polychaeta Sigalionidae Flabillligeridae Aphroditacea Sigalionidae Aphroditacea Nemertina unidentified Crustacea Ostracoda Podocopoa Podocopa Myodocopa Myodocopa Copepoda O. calanoida Ateidopsis sp. Undinopsis sp. Undinopsis sp. Oothrix sp. Slephos sp. O. harpactcoida Aegisthus sp. O. cyclopoida Oncaea sp. Malacostraca O. Mysidacea Tribe Erythropini Paramblyops sp.? Pseudomma sp.? unidentified unidentified O. cumacea Dyastilidae Dyastilidae Bodotriidae O. tanaidacea unidentified unidentified O. isopoda S. O. asellota Eurycopidae Haploniscus sp. Haploniscidae Eurycopidae O. amphidpoda S. O. Gammaridea Monoculodes sp. Monoculodes sp. Orchomene sp. Orchomene sp. Aora sp. Phoxocephalidae Leucolhoe sp. Oedicerotidae O. decapoda Ponlophylus sp. Ponlophylus sp. unidentified Munidopsis sp. eggs decapod unidentified Mollusca Gasteropoda Turridae Turridae Naticidae Bivalvia Limopsis sp. Others Foraminifers and sand in both species

(Fig. 6a). The infundibulum was composed of radially arranged cushions (Fig. 6b) as in all octopods (Nixon and Dilly, 1977), and the surface cuticle presented small, rounded pegs of 2.5 ~m of diameter. These pegs were composed by aggregations of minute rods, so that there are spaces or pores of 0.1-0.15 ~m of diameter. The density of pegs proved to be similar for both species, ranging from 14,500 to 17,000 pegs'mm-2 (Fig. 7a, b). Sucker surface cuticle was covered by ovoid structures (5-6 ~m of diameter), from the base of the peduncle to the limit between rim and infundibulum. Most of these structures were damaged, probably due to osmotic shock during fixation (Fig. 7c). Microvilli, of 0.12 ~m in the base and 0.14 ~m in the top end, covered the ovoid structures (Fig. 7d). The length of the cirri was similar in the two species, and varied between 0.5 mm in the distal end of the arms and 5 mm in the middle area of the arms of large individuals. Optical microscopy permitted us to observe muscle tissue inside the cirri (Fig. 8a), probably equivalent to the retractile muscle of the cirri described 294 BULLETIN OF MARINE SCIENCE. VOL. 49. NO. 1-2. 1991

Table 3. Ocurrence of food categories by weight, in the stomach contents of Opisthoteuthis agassizi and O. vossi

O. agassiz; O. vossi

Total <500 g >500 g Total 500 g N = 125 N - 78 N =41 N = 93 N = 52 N = 41

Food category No. (%) (%) (%) No. (%) (%) (%) Polychaeta 38 15.9 14.4 20.2 30 16.3 14.1 18.2 Nemertina 1 0.4 0.7 Ostracoda 15 6.3 4.8 5.9 II 5.9 6.1 5.7 Copepoda 19 7.9 8.9 5.9 10 5.3 4 6.8 Mysidacea 25 10.5 11 9.5 15 8 8.1 7.9 Cumacea 4 1.7 1.3 2.4 2 1.1 I 1.1 Tanaidacea 22 9.2 9.6 8.3 7 3.7 3 4.5 Isopoda 10 4.2 0.7 10.7 23 12.1 15.1 9.1 Amphipoda 36 15.1 16.4 11.9 36 19.2 23.2 14.8 Decapoda 24 10 11 9.5 18 9.6 5 14.8 Gastropoda 2 0.8 0.7 1.3 5 2.7 2.1 3.4 Bivalvia 6 2.5 2.7 2.5 4 2.2 2.1 2.3 Crustacea unidentified 37 15.5 17.8 11.9 26 13.9 16.2 11.4

by Meyer (1906) for Opisthoteuthis depressa. A tissue composed of apparently sensory cells covered the muscle tissue (Fig. 8b), but the septa described in the cirri of Cirrothauma murrayi by Aldred et al. (1983) were not observed. U sing scanning electron microscopy denoted that the surface of the cirri ap- peared as hillocks with pores in the apices (Fig. 9a). These pores were 2.5-7.8 ~m in diameter in O. agassizi and 2-5 ~m in O. vossi (Fig. 9b). The surface was covered by ovoid structures and microvilli as observed in the suckers (Fig. 9b). Tufts of microvilli covered the fusiform formations that constitute the surface cuticle of the cirri (Fig. 9c, d). Except in the abovementioned areas no microvilli were observed in the rest of the surface cuticle of the ventral side of the arm.

DISCUSSION Length/weight relationships demonstrate that males of both cirrate species grow larger and heavier that the females. Furthermore, males of O. agassizi are larger than those of O. vossi, while females of both species are similar in size. Published literature provides limited data on abundances of cirrate species. Pereyra (1965) estimat(~d abundances of 1indiv' h -I of Opisthoteuthis californiana off the Colombia River mouth (NE Pacific), at 686 m and 823 m depth. Photographs in the Virgin Islands basin (3,900 m depth) revealed densities of up to 98 cirrates' km-2 (Roper and Brundage, 1972) while those taken in the Arctic Ocean resulted in abundances of 2,000 cirrates' km -2 (2,360-3,786 m depth, Pearcy and Beal, 1973). Finally, Vecchione (1987) estimated between 0.3-3.33 cirrates·h-I north of the Bahamas at 1,093-5,043 m depth. The maximum estimates found in the present study (499 indiv' km-2 of O. vossz) suggest that the high densities obtained by Pearcy and Beal (1973) may not have been overestimated because of attraction to lights, as suggested by the authors. Food and Feeding. -Although several studies have provided data on stomach contents of cirrate octopods (Meyer, 1906; Scott, 1910; Ebersbach, 1915; Robson, 1930; Voss, 1956; Pereyra, 1965; Alcazar and Ortea, 1981; Vecchione, 1987), less than 10 individuals per species were analyzed in these contributions. Prey types included polycha.etes, copepods, mysids, isopods, amphipods and decapods. VILLANUEVA AND GUERRA: FEEDING ECOLOGY IN OP/STHOTEUTH1S 295

Figure 6. a. SuckerofO. agassizi. Scale = 0.75 mm. b. Sucker ofO. agassizi. Scale = 0.75 mm. (r- rim; si-sucker infundibulum; sp-sucker peduncle).

With the exception ofthe "fish fragments" recorded in stomachs of Opisthoteuthis depressa by Meyer (1906), prey categories found in the present paper seem to coincide with previous studies. Thus, capturing and feeding on small prey seems to be the pattern in both O. agassizi and O. vossi. Benthic species belonging to the epibenthic and suprabenthic fauna are the major prey items, with the exception of the few calanoid copepods observed (Table 2). It is interesting to note that whole crustacean prey items ranged between 1 and 8 mm in total length, and, with the possible exception of the copepod Oncaea conifera, no species cited as bioluminescent (Herring, 1978) were observed in the stomachs. No conspicuous feeding rhythm was observed in the studied species. Males and females seem to feed on similar prey categories, regardless of size, at all times of the day. Surprisingly, higher abundances of O. vossi were recorded during the night. This finding could imply a change in activity independent of feeding, but further studies are necessary to put forward conclusions in this respect. Suckers and Cirri Ultrastructure and Prey Detection Implications. - The optic nervous system in cirrate octopods is severely reduced in comparison with other octopods. Furthermore, the superior frontal lobe is small while the inferior frontal lobe is large, which emphasizes the importance of the receptors of the arms in these animals (Young, 1977; Aldred et a1. 1983). Morphological studies on the suckers of incirrate octopods and their innervation (Graziadei, 1962; 1964; 1965; 1971; Graziadei and Gagne, 1973; 1976; Nixon and Dilly, 1977; Kier and Smith, 1990) have pointed out the sensitivity of the suckers. However, cirrate octopods have been less studied in this respect (Meyer, 1906; Nixon and Dilly, 1977; Young, 1977; Aldred et a1., 1983). The small size of the suckers of the studied species (2-3 mm of diameter) suggest a relationship with the detection and capture of small prey. The surface of the infundibulum of O. agassizi and O. vossi is similar to that of Cirrothauma murrayi (Aldred et a1., 1983), with respect to size and structure of pegs and pores. The presence of dense microvilli covering the suckers of the studied species has not been observed in other cirrate species. There microvilli are probably related to chemoreception functions like the chemoreceptor cells T2 described in Octopus vulgaris (Graziadei and Gagne, 1976). Although 296 BULLETIN OF MARINE SCIENCE, VOL. 49, NO. 1-2,1991

Figure 7. a. Infundibulum pegs of the sucker of O. agassizi. Scale = 50 j.lm. b. Infundibulum of the sucker of O. agassizi, showing pegs and the pores covering their surface. Scale = 6 j.lm. c. Sucker peduncle surface of O. agassizi showing the ovoid structures; most of these were damaged, probably due to osmotic shock during fixation. Scale = 20 j.lm. d. Microvilli of the sucker rim surface of O. vossi. Scale = 311m.

different mechanoreceptor cells have been observed in the suckers of O. vulgaris (Graziadei and Gagne, 1976), no such structures have so far been found in cirrates. The presence of copepod exuviae in the stomachs of O. agassizi and O. vossi suggests that, even though exuviae may also present chemical signals, the mech- anoreception memory may play an important role when recognizing possible prey items. Cirri of Opisthoteuthis depressa have retractile muscle as well as secretory cells and "chemical-sinus" (Meyer, 1906). Abundant secretory cells, "olfactory-like" cells and cilia have been observed in the surface of cirri of Vampyroteuthis infernalis (Nixon and Dilly, 1977). O. vossi and O. agassizi do not have cilia, but rather dense microvilli and fusiform structures, perhaps acting as the olfactory- like cells of V. infernalis. The gelatinous consistency of cirrates suggests that they are neutrally buoyant (Denton, 1974; Clarke et al., 1979; Aldred et al., 1983). Observations in aquaria (Pereyra, 1965) and in-situ videotapes that were show VILLANUEVA AND GUERRA: FEEDING ECOLOGY IN OPlSTHOTEUTlfIS 297

Figure 8. a. Sagittal section through a cirrus of O. agassizi. (haematoxylin-eosin), x 100. Scale = 0.25 mm. b. Sagittal section through a cirrus of O. agassizi shows the cuticle surface and muscular tissue. (Haematoxylin-eosin), x 600. Scale = 25 /Lm.

Figure 9. a. Cirrus of O. agassizi under scanning electron microscope. Scale = 0.5 mm. b. Hillocks on the surface of cirri of O. agassizi, showing ovoid structures and pores. Scale = 20 /Lm. c. Cirri of O. vossi, sensory cuticle, showing tufts of microvilli covering the fusiform formations. Scale for lower half: 0.6 mm; upper = 60 /Lm. d. Microvilli covering the surface of the cirri of O. vossi. Scale = 3 /Lm. 298 BULLETIN OF MARINE SCIENCE. VOL. 49. NO. 1-2. 1991 by Dr. M. Vecchione, during the Symposium "Systematics, biology and fisheries of recent cephalopods", Woods Hole, June 1990, showed that Opisthoteuthis move with low swimming speeds. This fact could imply a lack of adaptation for the capture of fast swimming prey, as confirmed by the lack of fish or other cephalopods in the stomachs of O. agassizi and O. vossi. This study suggests that O. agassizi and O. vossi feed continuously throughout the day, although the higher densities recorded during nighttime hours may suggest a migratory behavior, apparently not related to feeding activities. Prey items include small-sized organisms with low swimming speeds, suggesting the use of chemoreceptors to detect prey items, followed by capture involving mechanore- ception. Morphological analysis reinforces this last statement; observation of well developed receptor structures on cirri and suckers suggest a predominance of chemical and tactile senses in the feeding strategies of the cirrate octopods O. agassizi and O. vossi.

ACKNOWLEDGMENTS Specialists in different zoological groups helped in the identification of stomach contents: Dr. E. Macpherson (Instituto de Ciencias del Mar, ICM, Barcelona, Spain) for decapods; Mrs. M. Carola and Mrs. C. Comet (Departament d'Ecologia, Facultat de Biologia, Barcelona, Spain) for copepods and amphipods respectively; Mr. D. Martin (Centre d'Estudis Avancats de Blanes, Girona, Spain) for polychaetes, and Mr. Ll. Dantart and Mr. C. San Vicente (Departament de Zoologia Invertebrats, Facultat de Biologia) for gast:ropods and bivalves, and mysids, respectively. Dr. S. v. Boletzky (La- boratoire Arago, Banyuls-sur-Mer, France) provided interesting comments on suckers and cirri ultrastructure. Mr. M. Barange advised on statistical tests and Mr. J. Mas-Riera on histological techniques, both providing interesting suggestions on earlier drafts of the manuscripts (both of ICM, Barcelona, Spain). Technical advice and suggestions of Dr. B. G. Castro and Mrs. M. T. Fernandez (Instituto de Investigaciones Marinas, Vigo, Spain) are acknowledged. Mr. J. M. Fortuno took the scanning microscope pictures and offered interesting suggestions. Funding was provided by the project "Investi- gaciones en las costas de Namibia" of the Instituto de Ciencias del Mar, Barcelona, Spain.

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DATEACCEPTED: December 5, 1990.

ADDRESSES:(R. V.) Instituto de Ciencias del Mar, Paseo Nacional sin, 08039-Barcelona, Spain; (A.G.) Instituto de Investigaciones Marinas, Eduardo Cabello 6, 36208- VIGO, Spain.