Cornelia Schmid, Nils Brenke, Johann Wolfgang Wägele 2. Abstract. Introduction. Material and methods

Transcription

1 Org. Divers. Evol. 2, Electr. Suppl. 1: 1-29 (2002) Gesellschaft für Biologische Systematik On abyssal isopods (Crustacea: Isopoda: Asellota) from the Angola Basin: Eurycope tumidicarpus n. sp. and redescription of Acanthocope galathea Wolff, Cornelia Schmid, Nils Brenke, Johann Wolfgang Wägele 2 Lehrstuhl Spezielle Zoologie, Ruhr-Universität Bochum, Germany Received 4 October 2001 Accepted 15 December 2001 Abstract Rich samples of benthic Peracarida collected from abyssal plains of the Angola Basin (South Atlantic) contained several new and rare asellote isopods. In this contribution, Eurycope tumidicarpus n. sp. is described from well-preserved specimens. This species is remarkable because the second pereopod has an enlarged carpus, and pereopod 4 is shaped like the posterior swimming legs. New specimens of Acanthocope galathea Wolff, 1962 are used for a redescription, hitherto unknown characters of the male are shown. Introduction During the DIVA 1 expedition with RV Meteor (cruise M48/1) abyssal deep-sea organisms were collected with an epibenthic sledge along a transect of about 700 km in the Angola Basin, off West Africa. The aim of this expedition is the study of biodiversity in oceanic abyssal plains. Before general conclusions are possible, the inventory of this fauna has to be completed. The present contribution is part of a series of taxonomic studies which are the basis for future biogeographical and ecological analyses. We describe herein a new species of Eurycope, and offer new data on a very conspicuous Acanthocope (A. galathea Wolff, 1962) based on excellently preserved specimens. Material and methods Specimens were collected with an epibenthic sledge modified after Brandt & Barthel (1995). Samples were washed through a 0.3 mm sieve with sea water, and fixed in cold ethanol. Drawings of whole specimens and of dissected parts were prepared using a camera lucida on different microscopes. Specimens of the new species are deposited in the Zoologisches Museum Berlin (ZMB), Germany. Abbreviations: A1: antenna 1 (antennula); A2: antenna 2 (antenna); Epip: epipod; juv.: juvenile; l.: left; l.m.: lacinia mobilis; Md: mandible; Mx1, 2: maxilla 1 and 2, respectively; P1-7: pereopods 1-7; Plp 1-5: pleopods 1-5; p.i.: pars incisiva; p.m.: pars molaris; Pr: pereonite; r.: right; Urp: uropod. 1 Results of the DIVA 1 expedition (cruise M48/1 of RV Meteor ) 2 Corresponding author: Johann Wolfgang Wägele, Lehrstuhl Spezielle Zoologie, Fakultät Biologie, Ruhr-Universität Bochum, D Bochum, Germany; johann.w.waegele@ruhr-uni-bochum.de

2 Schmid & al.: Abyssal Isopoda from the Angola Basin 2 Taxonomy Isopoda Asellota Family Munnopsidae Sars, 1897 Acanthocope galathea Wolff, 1962 (Figs 1-11) Material: 14 specimens from station St.318 (cruise M48/1 of RV Meteor ): S E S E, m; 1 specimen from St.320: S E S E, m; 11 specimens from St.338: S E S E, m; 1 specimen from St.339: S E S E, m; 4 specimens from St.344: S E S E, m;42 specimens from St.348: S E S E, m; 56 specimens from St.350: 'S 'E 'S ' E, depth 5389 m. All samples collected with an epibenthic sledge, except St.339 (Agassiz trawl). Diagnosis: Species showing the typical combination of characters of the genus Acanthocope (among others: at least pereonite 7 and pleotelson fused dorsally; pleotelson longer than wide; lateral spines on pereonites elongate; 2 pairs of long lateral spines and a terminal spine on pleotelson; elongate, uniramous uropods; exopod of pleopod 3 with 2 swimming setae; straight last article of mandibular palp; carpus of pereopods 5-7 flat, sickle-shaped), and in addition: first peduncular article of antennula without spine; pereonites 2-4 each with a long and slender dorsomedial spine, pereonite 1 without dorsomedian spine; one pair of short dorsal spines on pereonites 5, 6 and 7, but no additional short spines; lateral supracoxal spines on pereonites 2-7 long, slender, serrated; pleotelson dorsally smooth, terminal telsonic spine about as long as pleotelson; uniramous uropods somewhat longer than caudal telsonic spine. Description of immature male: Body elongate (Fig. 1), about 3.2 times longer than wide, pereonites 1 to 5 only slightly increasing in width, pereonites 6-7 narrower than pereonite 5. Pereonite 5 widest. Pereonites 5-7 and pleotelson dorsally fused. Pleotelson little narrower than pereonites, little wider than half of pereonite 7. Integument transparent, the alimentary canal and muscles are clearly visible. Cuticle smooth. Cephalothorax as wide as pereonite I, length only half of width. Vertex medially vaulted, ventral margin straight and frons bent downwards. No rostral point. Eyes absent. Antennulae and antennae insert dorsally. Clypeus and distal articles of mandibular palp visible in situ in dorsal view. Pereonites 1-4 with separate tergites. Anterior margins convex, posterior margins concave. Pereonite 1 narrower and shorter than the following somites. Each segment with rounded lateral lobes, armed with few denticles. Pereonites 2-4 with a supracoxal, dorsolateral, long and slender spine on tergal lobes, directed anteriorly, curved somewhat upward and frontally, carrying a row of denticles along the posterodorsal margin. Pereonites 2-4 each with a long spine dorsomedially, shape similar to lateral spines inserted near anterior margin, with denticles, curved somewhat upward and forward; longest spine on pereonite 2, shortest on pereonite 4. Pereonites 5-7 (natasoma) fused with each other and with pleotelson, together little longer than cephalothorax + pereonites 1-4. Lateral tergal lobes rounded, directed to posterior, armed with small denticles, lateral spines inserting on anterior margin, formed as on anterior pereonites. On pereonites 5 and 6 spines directed to anterior and somewhat upward. Lateral spines of pereonite 7 directed to posterior. Dorsal and ventral margins of the spines with rows of denticles. Each segment dorsally near midline with a pair of short, only slightly curved spines (shorter than 1 / 4 length of the dorsal spine of pereonite 4). Pleotelson completely fused with natasoma, excluding terminal spine about one third of total body length, slightly vaulted along midline, only few tiny setae laterally. Two pairs of lateral spines, shape similar to pereonal spines, but less curved, narrow terminal spine nearly as long as pleotelson (see Fig. 1). Narrowest parts of pleotelson near fusion line with pereonite 7, and anterior to the second pair of lateral spines; widest areas where lateral spines insert. Sharp ridges between dorsal and lateral areas of pleotelson, ridge margin curved upwards in area near spine insertions. A conspicuous ventral, pointed protrusion posterior to the branchial chamber (see lateral view, Fig. 1). Antennulae (Fig. 3) dorsolaterally on cephalothorax, behind antennae, length 0.6 of body length. Peduncle of 3 articles, flagellum multiarticulate. Article 1 largest, twice as long as wide, ventrally vaulted; several little teeth and a fine texture medially. Article 2 emerges dorsally and subapically, about 0.3 of length of article 1, last third wider, with 3 plumose setae and 1 simple seta. Following articles cylindrical. Article 3 more slender than article 2, article 4 (first flagellar article) short, half of article 3, with 2 plumose setae. Following area of flagellum long, with several

3 Schmid & al.: Abyssal Isopoda from the Angola Basin 3 incompletely separated articles, remaining flagellum with more than 40 articles. Antennae (Figs 1, 4) longer than body, inserting nearly frontally on cephalothorax, peduncle of 5 articles, flagellum mutliarticulate (incomplete in preserved specimen). Article 1 short, trapezoidal, with ventral denticles. Article 2 twice as long as wide, with few tiny denticles and few, very short setae, a stout, slightly curved spine ventromedially, longer than article; a smaller, pointed apical spine laterally. Article 3 short (about 0.6 of article 3), more slender than article 2. Article 4 longest, longer than natasoma, slender (length 36 times width), armed with denticles and few tiny setae. Article 5 (bent in Fig. 4) nearly same width as preceding article, but only 10 times longer than wide. Flagellar articles maximally 2 / 3 width of article 5, flagellum consisting of at least 23 articles (distal ones not preserved). Mandibles (Figs 5, 6) asymmetrical. Palp with 3 articles, first article longest, third smallest (0.8 of first article), with spines laterally and one stout, short, terminal spine. Condyle trapezoidal, proximal of insertion of palp. Pars molaris strong, apex broadened, obliquely cut off distally, 2 strong setae at lower margin of grinding surface. Lacinia mobilis of left mandible with two wide teeth with deep concavity separating them, one of them notched; spine row with 2 stout and blunt spines and 4 more finely serrated spines. Pars incisiva with two teeth, the dorsal one two times broader than long, with distal edge rounded and proximal one pointed. Teeth of right pars incisiva indistinct, depending of angle of view a notch can be visible. Lacinia of right mandible probably reduced (or transformed to a spine), spine row of 4 blunt and 3 pointed, serrated spines. Below pars molaris short rows of scale-like setae. Maxillulae (Fig. 7): apex of outer endite with 12 stout and partly serrated medially curved spines and an additional shorter spine, some slender setae apically and on outer margin a few longer, slender setae, inner margin with rounded small denticles. Inner endite bearing long slender setae distally, lateral margin of endite with a conspicuous blade-like protrusion, bearing 2 setae on apical point. Maxillae (Fig. 7) with 3 lobes. Outer and central lobe similar: slender, somewhat medially curved, each with 4 long (0.4 of whole endite length) and curved spines. Inner margin of outer lobe bearing long, slender setae. Medial (inner) lobe as wide as outer and central lobes together, distally rounded, lateral and inner margin with long setae, apex bearing several setae and 3 short, setulose, blunt spines, a setulose spine on medial margin conspicuously longer. Maxilliped (Fig. 7) with slender protopod, lateral margin fringed with short hair-like setae, medially with 3 coupling hooks. Endite reaching to insertion of third palp article; between apical setae some short, stout spines. Palp of 5 articles. First article short, with lateral row of fine setae, second article longest, distally broadened, maximal width 2.3 of first article width; convex lateral margin with some straight setae. Article 3 smaller, trapezoidal, inner margin wavy, with 10 strong setae (some of them broken off) inserting ventrally. Article 4 emerges on lateral third of article 3, with long median projection which bears on margin several simple setae. Article 5 short, longer than wide, apex rounded, with 5 setae. Epipod rhomboidal, surpassing proximal half of second palpal article, median margin convex, distal part of lateral margin straight, only rows of short, scale-like hairs on surface. Pereopods inserting lateroventrally under tergal lobes (Fig. 1). Longest pereopod (P4) nearly as long as body length. Ratio of length of pereopods to length of pereopod 1 (= 2.04 mm): P2 = 1.16, P3 = 1.38, P4 = 1.5, P5 = 1.21, P6 = 1.37, P7 = Pereopods 1-4 (Figs 8, 9) subsimilar, slender; pereopod 1 distinctly shorter. Basis of pereopod 1 shortest, of pereopod III + IV longest, slightly curved with concave dorsal margin, simple slender setae and plumose setae proximally, ventrally with short curved spines (absent on pereopod 4). Ischium about 1 / 3 of basis length, distal part with few simple setae. Merus short, about half length of ischium, distally broadening. Carpus slender and elongate, in P2 and P3 about as long as basis, in P1 and P4 longer than basis. Carpus of pereopod I curved, ventral margin concave, with few setae; carpus of pereopods 2-4 nearly straight, with setae but also with short rows of cuticular scales. Carpus of pereopod 4 distinctly longer than those of anterior pereopods. Propodus of pereopods 1-4 cylindrical, shorter than carpus. Length of propodus increasing from pereopod 1 to pereopod 4. Propodus of pereopod 1 only half length of propodus of peropod 4. Dactylus always slender, pointed and with 2 apical setae-like claws and a single seta. Dactylus of pereopods times longer than dactylus of pereopod 1. Pereopods 5 7 (Figs 9, 10) swimming legs with bases distinctly shorter than bases of P1-5, distally wider than proximally. Dorsal margins of bases 5 and 6 proximally with a field of setae, most of them plumose, and a conspicuous long (half of basis length) distal spine ventrally. Basis 5 centrally on dorsal margin a pointed edge with a thick seta. Ischium becoming slender distally, nearly as long as basis. Merus nearly triangular, 0.3 (P5) to 0.25 (P7) of

4 Schmid & al.: Abyssal Isopoda from the Angola Basin 4 ischium length, slender proximally, distally wide, 2-3 short setae distally. Carpus sickle-shaped, broadest in proximal half (width about 0.3 length), in P5 and P6 wider than in P7, margins bearing long swimming setae, only proximal part of ventral margin without setae. Carpus of pereopod 5 little smaller than that of pereopod 6, carpus of pereopod 7 distinctly shorter (0.7 of P6) and more slender. Dorsal margin with more setae (P5 and P6 with 28, P7 with 15 swimming setae) than opposite margin (P5 and P6 with 9, P7 with 3 swimming setae). The middle swimming setae always the longest (on P5 0.8 of carpus length, on P7 0.6 of carpus length). Between the swimming setae always 2-3 simple short setae on ventral margin. Apex ventrally with fine spines. Propodus flat, elongate, oval, dorsal and ventral margin with swimming setae, on P5 and P6 shorter than carpus, on P7 as long as carpus; broadest part 0.17 (P5), 0.14 (P6), 0.12 (P7) of length. All propodi with some fine, curved setae between the swimming setae on dorsal margin, two simple seate distally (on dorsal and on ventral edge). Dactylus long and slender, flat, straight, with numerous tiny setae. On distal third of dactylus 6 and 7 a field of 3-4 longer setae; apically a dorsal spine-like claw and an additional shorter claw ventrally. Respiratory chamber occupying somewhat more than half of ventral length of pleotelson (Fig. 4), covered by pleopods 1 and 2. Left and right pleopod 1 medially fused, apically rounded, 5 times longer than wide, setation as in Fig. 11. This male specimen may be immature, pleopods 1 and 2 are not completely differentiated in comparison with males of other species. Pleopod 1 in situ covering endopod and exopod of pleopod 2. Pleopod 2 with large semicircular protopod, few setae on lateral margin, small, medially knoblike exopod apical of insertion of endopod, endopod small, bent, distal part only little longer than proximal part, not differentiated (probably immature). Pleopod 3 exopod not overlapping endopod, about as long as endopod, sickle-shaped, about 5 times longer than broadest proximal part, lateral margin with row of fine setae, 2 long apical swimming setae. Endopod broadly oval, inner margin straight, outer margin convex, parallel to endopod, distal end bevelled, with 3 swimming setae. Pleopod 4 with slender, somewhat curved exopod, littler longer than half of endopod length, no setae, endopod pear-shaped, without setae. Pleopod 5 uniramous, oval, no setae. Uropods (Fig. 9) uniramous, cylindrical, longer than terminal pleotelsonic spine, inserted beneath lateral spines of pleotelson apex. First article quite small, cylindrical, about 0.2 of total uropod length, article 2 long and slender, length 28 times width, with short spines and small simple setae, one plumose seta, apex with 2 simple setae. Description of immature female: Body shape (Fig. 2) similar to that of male, a little wider. Pereonites 1 to 4, lobes and lateral and dorsal spines with more numerous denticles. Pleotelson one third of body length and 1.1 times longer than wide. Lateral margin sharp and with denticles. Antennulae shorter than in male (Fig. 3), length only 0.2 of body length, 3 peduncular and 4 flagellar articles. First four articles similar to articles of male, but article 1 more vaulted, small teeth dorsally, no apical setae, no texture. Article 3 relatively longer than in male, article 4 ring-like, with two plumose setae. Next three articles differing from male, article 5 long, slender (15 times longer than wide), without setae, article 6 more slender than article 5 and 1 / 4 of length of article 5, with a distal aesthetasc. The last flagellar article short, 1 / 2 width of article 6, with 3 distal aesthetascs. Antennae with only 3 proximal joints preserved, these similar to articles of male. Mandibles (Fig. 6) with palpus reduced, much shorter than in male, about as long as molar process, 3 short and slender articles, without setae. Pars molaris as in male. Lacinia mobilis of left mandible consisting of two teeth. Spine rows as in male. Maxillulae, maxillae and maxilliped as in male. Pereopods similar to those of male. Ratio of pereopod length to length of pereopod 1 (= 2.93 mm): P2 = 1.07, P3 = 1.27, P4 = 1.27, (P5 broken off), P6 = 1.29, P7 = Pleopod 2 a vaulted, somewhat keeled operculum (Figs 2, 11), ventromedian area with a large protruding spine bearing denticles. Apex of operculum straight, lateral margin with some setae. Other pleopods similar to male pleopods. Uropods as in male, but with some more teeth and setae. Oostegites immature, present as small ventrally directed coxal lobes on pereopods 2 to 4. Description of juvenile stage: Seventh pereonite not completely developed, shorter and more slender than the other segments, lateral tergal lobes smaller and without spine armatures. Pereopods 7 absent, other pereopods relatively shorter than adult pereopods. Antennulae not completely developed (Fig. 3), first 4 articles similar to adult articles, article 5 enlarged, as long as articles 1-4 together and without setae. Next two articles similar to those of adult, both with aesthetascs. Remarks: The genus Acanthocope presently contains 15 species, all are deep-sea organisms. All species

5 Schmid & al.: Abyssal Isopoda from the Angola Basin 5 except A. galathea Wolff, 1962 and A. armata Chardy, 1972 have a long, acute spine on the first antennular article. The description of A. unicornis Menzies, 1962 is incomplete in this respect. Some species have a shorter terminal telsonic spine than the present material (A. annulatus Menzies, 1962, A. argentinae Menzies, 1962, A. curticauda Birstein, 1970). In A. annulatus Menzies, 1962, pereonites 5 and 6 seem to be unfused, or at least a distinct fusion line is present. A. argentinae Menzies, 1962 has numerous small dorsal spines, absent in A. galathea. The spine pattern is also useful to distinguish A. galathea from several other species. A. unicornis Menzies, 1962, A. spinosissima Menzies, 1956 and A. armata Chardy, 1972 have no dorsal spines on the anterior pereonites 1-3. A. spinicauda Beddard, 1886 and A. acutispina Beddard, 1886 differ in possessing a dorsal spine on pereonite 1 and an upcurved, collar-like anterior border of the cephalothorax. The pleotelson is dorsally keeled in A. carinata Chardy, 1972; A. orbus Menzies and George, 1972 has small spines on the cephalothorax and a pair of caudally directed spines dorsally on pereonites 5, 6 and 7; in A. pentacornis Müller, 1989 the dorsal spines on anterior pereonites are very long and the pleotelson has a sharp dorsal protrusion; A. muelleri Malyutina, 1999 has generally longer spines than the present material and the uropodal exopod is still present, though very small; in A. beddardi Malyutina, 1999 the dorsal surface bears many tiny spines; in A. mendeleevi Malyutina, 1998 the pleotelson bears a long dorsal spine. Our material agrees well with the characters of the species mentioned by Wolff (1962) and Malyutina (1999). Wolff described a female which was found in the Gulf of Panama (05 49 N, W) at a depth of m. His material did not have a complete antenna. The second description was prepared by Malyutina (1999) for a female specimen which was found in the South Atlantic Ocean (31 24,8 S, W) at a depth of 4725 m; this specimen was 5.9 mm long and without a complete antenna. The present new material is more similar to the one used by Malyutina, the localities are from the same area (west of the Walvis Ridge), though about 1000 km apart. The new material contains a nearly mature male with a more complete antenna. The sexually dimorphic characters are described for the first time. Antennulae in males are elongate in comparison with females, mainly due to the presence of additional flagellar articles, a character probably related to a more efficient olfaction. The mandibles are sexually dimorphic with regard to their palpus. The female palpus is shortened and may be overlooked. The palpus in males is normal, clearly visible. An ultimate decision whether the Caribbean specimens are really conspecific with the ones from the southwest Atlantic is not possible with the available data. The distance between the localities is large, populations are separated by the Midatlantic Ridge, gene flow should be very reduced, if it occurs at all. The known morphological differences are small and give no clue (Malyutina 1999). Eurycope tumidicarpus n. sp. Material: Holotype (ZMB 27400): male, 3.59 mm, collected from station 350 of cruise M48/1 with RV Meteor ( 'S 'E 'S ' E, depth 5389 m). Paratype (ZMB 27400): male, 3.9 mm, from Sta. 348 ( S E S E, m). Diagnosis: Species with the diagnostic characters of Eurycope Sars, 1864 (see Wilson & Hessler 1981, Wägele 1989, Wilson 1989). Rostrum present but short, rounded, with two setae; width of cephalothorax about 0.7 of maximal body width; pereonite 5 about as long as pereonite 6 and with roughly parallel lateral margins, with rounded posterior edges; pereonite 7 more than twice length of pereonite 6; pleotelson wider than long, about as long as pereonite 7, without lateral or terminal projections, tip bent downward. Broad antennular article 1 three times wider than second article, with medial lobe bearing apically 4 spines, second article as long as first article. Carpus of pereopod 2 widened, broadly oval. Ischium, carpus, and propodus of pereopod 4 somewhat expanded and furnished with swimming setae, merus with a single swimming seta. Male pleopod 1 medially with 5 hemiplumose setae on ventral surface, distal tip of inner apical lobes rounded. Pleopod 2 with 7 proximolateral hemiplumose setae, protopod apically with small distal projection (vermiform appendage) bearing 2 short, hemiplumose terminal setae. Uropodal protopod with rounded medial projection, exopod smaller than half length of endopod. Description of male: Body long, oval, with finely lined cuticular texture (Fig. 12). Cephalic lateral margins parallel, cephalothorax little narrower than pereonite 1, more than 3 times wider than long. Rostrum short, apically rounded, with small lateral keels, lacking overhang, 2 apical long setae (length 0.07 mm in holotype, width 0.38 length) (details in Figs 12, 13). Width of each segment from cephalothorax to pereonite 4 increasing, pereonite 5 broadest

6 Schmid & al.: Abyssal Isopoda from the Angola Basin 6 (1.31 mm). Approximate length relationships of tergites along midline: 1 = 2 = 3 < 4 < 5 = 6 < 7. Pleotelson shorter than pereonite 7, smooth, rounded. Pereonites 1-4 subequal in height, 5-7 distinctly deeper. Pereonites 1-4 with distinct intersegmental membranes, anterior margins convex, posterior ones concave. Lateral tergal lobes rounded, each with anterior point, flat supracoxal lobes with projecting anterior point, separated from tergites by distinct suture on pereonites 1-4. Tergal articulations of pereonites 5-7 distinct, sternites with distinct cuticular texture, tergites with weak cuticular texture. Pereonites 5 and 6 subequal, anterior margins convex, posterior ones concave, no distinct supracoxal lobes; anterior point of lateral tergite margins with 2 small apical setae. Pereonite 7 longest, 0.26 of total body length, anterior margin convex, posterior one concave, laterally in pleural area a long seta (detail in Fig. 13). Insertion of pereopods 5-7 on posterior border of pereonites. Sternites with some setae. Pleotelson length 0.75 width, posterior margin smoothly rounded, anterolateral edges with a short seta and dorsolaterally 2-3 fine setae. In front of the ventral uropod insertion a row of long, fine setae along articular margin. Uropodal endopodites and part of exopodite visible in dorsal view. Antennula (Fig. 14) nearly half of body length, with 3 peduncular articles, long flagellum. First article large and broad, with several tiny spines and few plumose setae, distal part much broader than insertion of second article, maximal width nearly four times basal part of second article. Medial distal margin with 4 spines, lateral margin with 1 spine. Article 2 shorter than article 1, distally 4 plumose setae and several spines. Third article shorter and more slender than first articles, with some fine setae. Short first flagellar article only 1 / 3 length of article 3, but same width, ringshaped, distomedially 2 plumose setae and 2 simple setae. Following flagellar articles subequal, distal ones shorter and smaller. First 8 articles with distolateral short setae, remaining articles each with one long athestasc. Some articles (22, 24) with slender, simple setae. One apical plumose seta and a single simple seta on last article. Antenna (Fig. 14) 2.6 times body length, with 4 broad, and 2 long, slender peduncular articles and more than 70 flagellar articles. First and second article short. First article (not seen in Fig. 14) with 1 lateral spine, second article with 2 lateral spines. Third article longer than the first articles, laterodistally with broad scale, which possesses 5 sensory spines with distal sensillum. Article 5 slender and long, 15 times longer than wide, with many small sensory spines. Article 6 slender, same length as fifth, fewer spines, 4 distal plumose setae and 4 simple setae which are longer than next article. Following flagellar articles subequal in width, differing in length. Distal articles with one apical seta. Mandible (Fig. 15) palp of 3 articles, little shorter than corpus mandibulae. First article shortest, distolaterally 2 small setae. Second article 3 times longer than article 1, laterally with 10 long, slender setae, apically 3 stout spines, one of them setulose. Article 3 flattened, strongly curled laterally, with medial row of fine setae, internal side with spine row, distal spines shorter, stout and partly setulose, on apex a long spine of half length of article 2. Pars molaris broad, stout, and with toothed lower margin and 6 setae on right and 7 on left mandible. Left lacinia mobilis broad, with 7 teeth. Right mandible lacinia resembling a broad spine of the spine row (?). Spine rows with 6 notched or serrated spines, proximal ones more slender. Pars incisiva on both mandibles formed by 3 heavily sclerotized, rounded teeth, central tooth longest. Condyle length subequal to pars molaris. Outer endite of maxillula (Fig. 16) more than twice width of inner endite, surfaces of both endites with scattered long setae. Lateral endite with 12 spine-like teeth: 3 short unilaterally serrated spines dorsally, other spines partly longer, not serrated. The smaller inner endite broadened proximally, lateral margin convex, on apex 14 long setae and 2-3 smaller, stout spines. Maxilla (Fig. 16) with 3 endites. Central endite and outer endite equal in width, outer endite longest, surface with scattered slender setae. Apices of lateral and central endite each distally with long, stout setae (3 on lateral, 2 on central endite) and 1 shorter setulose seta. Inner endite broad, about twice as wide as lateral endite, inner margin with row of long setae and basal region of inner margin with two rows, each of 6-7 tiny denticles or spines. 17 long setae and 8 small setae distally, a proximal one robust, longest, pointing medially. Maxilliped (Fig. 16) with 5 retinacula (coupling hooks). Epipodite shaped like a broad ypsilon, with concavity on lateral margin. A stout sensory spine on ventral surface of coxa, basis with 2-3 such spines. Basis lateral margin fringed with fine, short setae, a dorsal field of about 20 fine setae, and dorsally and ventrally on margin of articulation of palp 1 single, small spine. Endite shovel-shaped, with many long setae on margins and row of 6 fan setae on distal margin. Palp of 5 articles, articles 2 and 3 forming together an oval plate. First article broader than long, lateral margin fringed with setae, dorsally and ventrally one small spine on distal margin. Article 2

7 Schmid & al.: Abyssal Isopoda from the Angola Basin 7 increasing in width distally, 3 times longer than article 1, lateral margin with 7 stout setae, 2 long stout setae distomedially. Article 3 trapezoidal, medial margin with row of setulose setae and 8 long simple setae distally. Few fine setae near article 4 insertion. Article 4 with a medial lobe smaller than article 5, long setae distally. Article 5 smallest, more than 3 times longer than wide, with long setae on lateral and medial margins and 4 long setae apically. Pereopods 1-3 ambulatory, pereopod 2 with unusually broad carpus, pereopod 4 similar to swimming legs, pereopods 5-7 typical munnopsid swimming legs. Length ratios of pereopods relative to pereopod 1 (2.94 mm): P2 = 1.50; P3 = 1.63; P4 = 0.95, (P5 distally broken off); P6 = 0.82; P7 = Pereopods 1-4 (Figs 17, 18): Bases of approximately same length, basis of P4 (not drawn) somewhat shorter. Dorsal margin proximally always with 2-3 plumose setae, ventral margin with one dorsodistal spine, several setae all over dorsal surface. Ischium 1 short, ischia 2 and 3 twice ischium 1 length, ischium 4 as long as ischium 1 but of different shape. Ischia 1-3 narrow, cylindrical, simple setae scattered all over their surfaces. Ischium 4 unusually flattened and widened, dorsally with convex margin and fringed with 12 swimming setae. Merus short, but increasing in length from P1 to P3, on P4 distinctly shorter, on P1-3 cylindrical, with simple setae, on P4 broader distally, with one distal swimming seta. Carpi with increasing length, being longest article of P1 and P2. Carpi of P1 and P3 cylindrical, slender, 4 times longer than merus, carpus of P2 swollen, dorsal margin strongly convex, setae scattered all over surface, many simple setae on dorsal margin, fine sensory spines. Long setae on distal end of carpi 1-3, on P2 with an additional, plumose seta. Carpus of P4 flat, oval, similar to carpus of following natatory pereopods, with 13 ventral and 18 dorsal swimming setae and slender sensory spine distodorsally. Propodus of P1-3 increasing in length, cylindrical in P1 and P3 only, longest in P3, propodus 4 as long as of P1 and as long as carpus 4. Propodus of P2 swollen basally, with dense dorsal setation (simple setae) and fine sensory spines with setulose sensilla (detail in Fig. 17) ventrally. Propodus of P2-4 distally with elongate setae and always 1 plumose seta. Propodus of P4 different, flat, widened (width 0.25 length), resembling propodus of P5-7, with 16 dorsal and 15 ventral swimming setae and dorsally with long setae and slender sensory spine on distodorsal apex. Dactylus always narrowest article. P1 with shortest dactylus (0.26 of propodus length), in P2 and P3 longer. P4 dactylus little shorter than dactylus 3, but broader and flattened. Always with 1 small seta, close to distal end of dactylus. Claws indistinct. Pereopods 5-7 (Figs 18, 19): bases similar in length, shorter than body height, except for basis 5 with few setae, on P5 lateral margin with 9 short setae. All bases with distal row of 2-4 sensory spines. Length of ischium becoming shorter from P5 to P7, narrower distally. Dorsal margin with swimming setae (P5: 6, P6: 9, P7: 8), ventral margin only with few, simple setae. Merus increasing in length posteriorly, proximally narrow, distally broadened, dorsal margin with 1 single swimming seta. Carpi flattened, oval. Carpus 5 shortest, of P6 longest, of P7 broadest. Always dorsal margin strongly convex, broadest part proximally, fringed with swimming setae (dorsally: P5 28, P6 26, P7 34; ventrally: P5 18, P6 21, P7 21), up to 3 sensory spines on dorsodistal edge. Propodi (broken off in P5) similar to carpi: flat and oval, but shorter, in P6 and P7 with few setae on posterior surface, ventral margin more convex than dorsal margin, margins fringed with swimming setae. Always 2 narrow apical sensory spines, one distoventrally, one distodorsally, an additional plumose seta distodorsally. Dactyli small, not more than 1 / 4 of corresponding carpus length, longoval. Ventral margin of P6 dactylus serrated. In last third 1 long seta, near distal tip a slender spine. Claws indistinct. Male pleopod 1 (Fig. 19) sympods medially fused, length 4 times width, distally slightly narrowing, ventrally with 5 hemiplumose setae on each side of midline, continuous with a row of small setae; a small protuberance on dorsal surface, covered with small cuticular scales. Inner apical lobes distally rounded, with 4-5 slender laterodistal spines and 12 apical setae. Only tips and lateral margins of outer lobes visible in ventral view, no lateral projections. Outer lobes distally narrow, apex rounded, distance between apical tips of outer lobes 0.12 mm in holotype. Pleopod 2 (Fig. 20) with triangular protopod, enlarged proximally, with lateral row of 7-8 hemiplumose setae. Protopodite width 0.44 mm in holotype, length of lateral margin 0.56 mm, 1 / 9 of length formed by distal vermiform appendage, which bears 2 hemiplumose setae. Exopod emerges in distomedial concavity of protopod, very setose proximally and bent medially. Endopod inserting proximal to exopod, seemingly of 3 articles; first article extends anteromedially, second article curved distally, third article being extension of preceding one. Both first articles of same length and width, pointed third article with proximal chamber connected distally to fine sperm tube; the latter ending on tip of endopod. Pleopod 3 protopod probably fused with endopod, endopod broad, nearly rectangular,

8 Schmid & al.: Abyssal Isopoda from the Angola Basin 8 twice as long as wide, on distal margin 3 stout swimming setae. Exopod sickle-shaped, bi-articulated, emerges on proximal edge of endopod, proximal width half width of endopod, distally narrowing, apically a stout seta, margins fringed with fine setae. Pleopod 4 with large endopod, length 1.3 width, no setae. Exopod bi-articulated, narrow, longer than endopod, margins setulose and one long apical swimming seta. Pleopod 5 nearly quadrangular, uniramous, no setae. Uropods (Fig. 17) short, biramous. Protopod distally broadening, as long as distal width. Protopodal laterodistal edge with 2 strong spines and lateral setae. Distal row of long setae, distomedially many elongate setae. Exopod and endopod both cylindrical, distally rounded. Exopod short, as long as proximal protopod width, with 3 fine distolateral setae and 4 stronger apical spines. Endopod more than twice length of exopod, twice as broad as exopod, with medial short setae, 3 lateral plumose setae on center of lateral margin, apically 6 plumose and 2 simple setae, and 3 strong spines. Female unknown. Derivation of name: tumid is a Latin adjective meaning "puffed-up". The name refers to the thickened carpus of the second pereopod. Remarks: A problem is that several species of Eurycope are incompletely described, either because parts were omitted or because the fragile specimens could not be collected undamaged. Therefore, it is not sufficient to compare the conspicuous structure of the pereopods 2 and 4 of the new material with the published descriptions, other appendages and structures are more frequently conserved. Several species of Eurycope have special shapes of the rostrum and therefore are easily distinguished from the new material (E. dahli, E. gibberifrons, E. latifrons, E linearis, E. nobili, E. ochotensis, E. producta, E. quadrata, E. septemtrionalis), others have differently shaped pereonites or a different form of the pleotelson. Species with a less conspicuous rostrum E. affinis Birstein, 1970, E. cornuta Sars, 1864, E. hessleri Wilson, 1983, E. lavis Schultz, 1978, and E. vasina Malyutina and Kussakin, 1996 have a mandibular palp as long as or longer than the corpus mandibulae, in our material the palp is shorter. In none of these species the peculiar, basally widened male pleopod 2 with its distal vermiform process is known. The most similar species are those described by Wilson (1983) as complanata-complex, named after E. complanata Bonnier, The known species of the complanata species complex are limited to the deep north Atlantic Ocean. They share the short rostrum, the pleural spine near the insertion of pereopod 7, the short mandibular palp, and the shape of male pleopod 2. The new material from the Angola basin belongs to a new species. It differs from all hitherto known species by the following combination of conspicuous characters: rostrum with 2 strong setae, no lateral spine on cephalothorax, second pereopod with broad carpus, fourth pereopod shaped as swimming legs 5-7, shape of distal parts of first pleopod (Fig. 19), configuration of second pleopod (Fig. 20), and length relation between uropodal exo- and endopod; the uropodal sympod is wider than long. Acknowledgments This is a contribution to the DIVA 1 project, supported by the Deutsche Forschungsgemeinschaft with grant Wa 530/27-1. We are grateful to the crew of RV Meteor for technical support under partly difficult weather conditions, and to the team of DIVA 1. We want to mention especially Dr. Michael Tuerkay (Senckenberg Museum, Frankfurt), leader of the expedition, and Prof. Angelika Brandt (Zoological Institute, University Hamburg) whom we thank for her cooperation and for sharing the samples with us. References Beddard, F. E. (1886): Report on the Isopoda collected by H.M.S. Challenger during the years Part 2. Rep. Voyage H.M.S. Challenger 17: Brandt, A. & Barthel, D. (1995): An improved supraand epibenthic sledge for catching Peracarida (Crustacea, Malacostraca). Ophelia 43: Birstein, J. A. (1970): Additions to the fauna of isopods (Crustacea, Isopoda) of the Kurile- Kamchatka-Trench [translation by Israel Program for Scientific Translation, Jerusalem 1972]. Part I. Trudy Inst. Okeanol. 86: Chardy, P. (1972): Le genre Acanthocope Beddard (Isopode, Asellote): description de deux espèces nouvelles. Remarques taxonomiques et biogeographiques. Bull. Mus. Hist. Nat. Ser (Zool. 30): Malyutina, M. V. (1998): Acanthocope mendeleevi: a new species of Munnopsidae (Crustacea, Isopoda, Asellota) from the New Caledonian Basin. Russ. J. Mar. Biol. 24: Malyutina, M. V. (1999): New species of Acanthocope (Isopoda, Munnopsidae) [in Russian]. Biol. Morya 25: Malyutina, M. V. & Kussakin, O. G. (1996): Additions to the Polar Sea bathyal and abyssal Isopoda

9 Schmid & al.: Abyssal Isopoda from the Angola Basin 9 (Crustacea, Malacostraca). Part 3. Asellota: Munnopsidae. Zoosyst. Rossica 5: Menzies, R. J. (1956): New bathyal Isopoda from the Caribbean with observations on their nutrition. Breviora 63: Menzies, R. J. (1962): The isopods of abyssal depths in the Atlantic Ocean. Vema Res. Ser. 1: Menzies, R. J. & George, R.Y. (1972): Isopod Crustacea of the Peru-Chile trench. Scientific Results of the Southeast Pacific Expedition. Anton Bruun Rept 9: Müller, H. G. (1989): Acanthocope pentacornis n.sp. from the deep sea of the Gulf of Aden. Senckenbergiana Maritima 20: Sars, G. O. (1864): Om en anomal Gruppe af Isopoder. Forh. Vidensk. Selsk. Krist. 1863: Schultz, G. A. (1978): More planktonic isopod crustaceans from Subantarctic and Antarctic seas. Ant. Res. Ser. 27: Wägele, J. W. (1989): Evolution und phylogenetisches System der Isopoda. Stand der Forschung und neue Erkenntnisse. Zoologica 140: Wilson, G. D. F. (1983): Systematics of a species complex in the deep-sea genus Eurycope, with a revision of six previously described species (Crustacea, Isopoda, Eurycopidae). Bull. Scripps Inst. Oceanogr. 25: Wilson, G. D. F (1989): A systematic revision of the deep-sea subfamily Lipomerinae of the isopod crustacean family Munnopsidae. Bull. Scripps Inst. Oceanogr. 27: Wilson, G. D. F. & Hessler, R. R. (1981): A revision of the genus Eurycope (Isopoda, Asellota) with descriptions of three new genera. J. Crust. Biol. 1: Wolff, T. (1962): The systematics and biology of bathyal and abyssal Isopoda Asellota. Scientific results of the Danish deep-sea expedition round the world Galathea Rep. 6:

10 Schmid & al.: Abyssal Isopoda from the Angola Basin 10 Fig. 1. Acanthocope galathea Wolff; male (3.3 mm length). a: lateral. b, c: dorsal.

11 Schmid & al.: Abyssal Isopoda from the Angola Basin 11 Fig. 2. Acanthocope galathea Wolff; juvenile female (4.6 mm length). a: lateral. b: dorsal. c: detail of oostegite anlagen. d: outline of posterior end of body, dorsal.

12 Schmid & al.: Abyssal Isopoda from the Angola Basin 12 Fig. 3. Acanthocope galathea Wolff; antennulae. a, b: juvenile (2.5 mm). c, d: female. e-g: male.

13 Schmid & al.: Abyssal Isopoda from the Angola Basin 13 Fig. 4. Acanthocope galathea Wolff; male: pleotelson (two views); second antenna.

14 Schmid & al.: Abyssal Isopoda from the Angola Basin 14 Fig. 5. Acanthocope galathea Wolff; male: mandibles.

15 Schmid & al.: Abyssal Isopoda from the Angola Basin 15 Fig. 6. Acanthocope galathea Wolff; female: mandibles.

16 Schmid & al.: Abyssal Isopoda from the Angola Basin 16 Fig. 7. Acanthocope galathea Wolff; male: mouthparts.

17 Schmid & al.: Abyssal Isopoda from the Angola Basin 17 Fig. 8. Acanthocope galathea Wolff; male: pereopods 1-3.

18 Schmid & al.: Abyssal Isopoda from the Angola Basin 18 Fig. 9. Acanthocope galathea Wolff; male: pereopods 4, 5; uropod.

19 Schmid & al.: Abyssal Isopoda from the Angola Basin 19 Fig. 10. Acanthocope galathea Wolff; male: pereopods 6 and 7.

20 Schmid & al.: Abyssal Isopoda from the Angola Basin 20 Fig. 11. Acanthocope galathea Wolff: pleopods.

21 Schmid & al.: Abyssal Isopoda from the Angola Basin 21 Fig. 12. Eurycope tumidicarpus n. sp.; male (holotype, 3.6 mm). a, b: details of rostrum. c: whole animal, dorsal. d: details of pleotelson, ventral. e: whole animal, lateral.

22 Schmid & al.: Abyssal Isopoda from the Angola Basin 22 Fig. 13. Eurycope tumidicarpus n. sp.; male (holotype). a: cephalothorax, lateral. b: pereonite 7, lateral; arrow points to pleural seta.

23 Schmid & al.: Abyssal Isopoda from the Angola Basin 23 Fig. 14. Eurycope tumidicarpus n. sp.; male (holotype). A1: antenna 1. A2: antenna 2; basal peduncle (a) enlarged in comparison with remaining articles (b).

24 Schmid & al.: Abyssal Isopoda from the Angola Basin 24 Fig. 15. Eurycope tumidicarpus n. sp.; male (holotype): mandibles, with enlarged details (a-e).

25 Schmid & al.: Abyssal Isopoda from the Angola Basin 25 Fig. 16. Eurycope tumidicarpus n. sp.; male (holotype): mouthparts.

26 Schmid & al.: Abyssal Isopoda from the Angola Basin 26 Fig. 17. Eurycope tumidicarpus n. sp.; male (holotype): pereopods 1, 2; uropod.

27 Schmid & al.: Abyssal Isopoda from the Angola Basin 27 Fig. 18. Eurycope tumidicarpus n. sp.; male (holotype): pereopods 3-5.

28 Schmid & al.: Abyssal Isopoda from the Angola Basin 28 Fig. 19. Eurycope tumidicarpus n. sp.; male (holotype): pereopods 6, 7; pleopod 1, lateral (a), dorsal (b), ventral (c).

29 Schmid & al.: Abyssal Isopoda from the Angola Basin 29 Fig. 20. Eurycope tumidicarpus n. sp.; male (holotype): pleopods 2-5.