Studies on the genus Onisimus Boeck, 1871 (Crustacea, Amphipoda, Lysianassoidea, Uristidae) I. The brevicaudatus and sextonae species groups

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1 Org. Divers. Evol. 5, Electr. Suppl. 7: 1-48 (2005) Gesellschaft für Biologische Systematik Studies on the genus Onisimus Boeck, 1871 (Crustacea, Amphipoda, Lysianassoidea, Uristidae) I. The brevicaudatus and sextonae species groups Wim Vader a, Jan Roger Johnsen a, Jørgen Berge b, * a Tromsø Museum, Dept. of Zoology, University of Tromsø, 9037 Tromsø, Norway b Dept. of Biology, UNIS, PO Box 156, 9171 Longyearbyen, Norway * Corresponding Author, jorgen.berge@unis.no Received 3 June 2004 Accepted 30 August 2004 Abstract Based upon a thesis (Johnsen 2001) on the taxonomy of the uristid genus Onisimus Boeck, 1871, the latter is divided into five species groups to be treated in this and forthcoming publications; a key to these groups includes the genera Menigrates Boeck and Paralibrotus Stephensen. Further keys and redescriptions are presented to all species within two Onisimus species groups. The O. brevicaudatus-group comprises the species O. affinis Hansen, 1886 (= O. dubius Schellenberg, 1935, syn. n.), O. botkini Birula, 1897, O. brevicaudatus Hansen, 1887, O. caricus Hansen, 1887, and O. derjugini Gurjanova, The O. sextonae-group consists of the species O. abyssi Oldevig, 1959, O. leucopis (G.O. Sars, 1879), and O. sextonae Chevreux, Keywords: Uristidae; Onisimus; O. brevicaudatus-group; O. sextonae-group Introduction The uristid amphipod genus Onisimus Boeck, 1871, a common and quite species-rich genus in high-latitude northern seas, has caused taxonomic problems for many years due to uncertainty concerning its type species. These problems, which also have led to the erection of the nominal genera Pseudalibrotus Della Valle, 1893, and Boeckosimus Barnard, 1969, have been extensively discussed and largely solved in the excellent paper by Lowry and Stoddart (1993). These authors redescribed the respective type species of the nominal genera Onisimus (= Pseudalibrotus auct.), Boeckosimus and Paronesimus, and synonymized all three under the oldest available name Onisimus Boeck, However, their study did not include details on all species of Onisimus s.l. they listed 26 nominal species and 4 species dubiae but concluded that the genus is in urgent need of revision (Lowry and Stoddart 1993: 169). Material and methods The present study is based mostly on material in the collections of Tromsø Museum (TMU). Additional important material was borrowed from the Smithsonian Institution (USNM), the Swedish Museum of Natural History (SMNH), and the Zoological Museum in Copenhagen (ZMC). Further material was provided by the Zoological Museum in Berlin (ZMB), the Zoological Museum in Oslo (ZMO), and the Zoological Museum in St. Petersburg. All dissected appendages were mounted in polyvinyl-lactophenol and stained with rose-bengal. Mature and immature females were distinguished from males by the presence of oostegites. Classification of setae and setae-groups follows Watling (1989) and Berge (2001). All scale bars in the figures represent 0.1 mm. Abbreviations used in the text and figures: A1-2 = antenna 1-2; EP1-3 = epimeral plate 1-3; I.P = inner plate; L = labium; LBR = labrum; LMND = left mandible; MX1 = maxilla 1; MX2 = maxilla 2; MXP = maxilliped; OP = outer plate; P1-7 = pereopod 1-7; PLP = palp; RMND = right mandible; ST = setal teeth (Mx 1); T = telson; U1-3 = uropod 1-3.

2 Vader & al.: Studies on Onisimus (Crustacea, Uristidae) I. 2 Systematics Family Uristidae Genus Onisimus Boeck, 1871 Onisimus Boeck, 1871: 111. Stebbing (1906: 25), Schellenberg (1927: 659), Stephensen (1929: 53), Gurjanova (1951: 161), Barnard (1969: 352), Barnard and Karaman (1991: 506), Lowry and Stoddart (1993: 168). Onesimus Boeck, 1876: 161; unjustified emendation. Sars (1891: 104). Alibrotus Sars, 1891: 101. Pseudalibrotus Della Valle, 1893: 798. Stebbing (1906: 33), Schellenberg (1927: 671), Stephensen (1929: 55). Paronesimus Stebbing, 1894: 14. Stebbing (1906: 43), Gurjanova (1951: 196), Barnard (1969: 357), Barnard and Karaman (1991: 516). Boeckosimus Barnard, 1969: 330. Barnard and Karaman (1991: 470). Nomenclature. According to Boeck (1876), the original spelling Onisimus was an inadvertent misprint of the intended spelling, Onesimus. However, as the original publication (Boeck 1871) itself does not contain clear evidence for this error, the spelling Onisimus must be maintained (ICZN 1999: Article ). For a thorough discussion of the nomenclature of this genus see Lowry and Stoddart (1993). Type species Anonyx litoralis Krøyer, 1846, by subsequent designation of Boeck (1876). Species included (25) Onisimus abyssi Oldevig, 1959; O. affinis Hansen, 1887 (= O. dubius Schellenberg, 1935, syn. n.); O. barentsi (Stebbing, 1894); O. birulai (Gurjanova, 1929); O. botkini Birula, 1897; O. brevicaudatus Hansen, 1887; O. caricus Hansen, 1887; O. caspius (Sars, 1896); O. derjugini Gurjanova, 1929; O. edwardsii (Krøyer, 1846); O. glacialis (Sars, 1900); O. krassini Gurjanova, 1951; O. leucopis (Sars, 1879); O. litoralis (Krøyer, 1845); O. nanseni (Sars, 1900); O. normani Sars, 1891; O. platyceras (Sars, 1896); O. plautus (Krøyer, 1845); O. punctatus (Bate, 1862); O. sextonae Chevreux, 1926; O. sibiricus Brüggen, 1909; O. simus Gurjanova, 1962; O. turgidus Sars, 1879; O. uschakovi (Gurjanova, 1933); O. zenkevitchi (Mednikov, 1960). Remarks At this time, 25 species names are considered as valid in the genus Onisimus, but some of them will be re-examined and possibly synonymised in later papers of the present series. In addition, Lowry and Stoddart (1993: 169) listed four nomina nuda O. abyssicola, O. vorax and O. zebra of Stuxberg (1880), and O. crassini of Gorbunov (1946) and suggested that O. punctatus should be considered a nomen dubium. Johnsen (2001) recently studied the taxonomy of the genus Onisimus for a MSc thesis at the University of Tromsø under the guidance of the first author. The series of works starting with the present paper largely builds on that thesis. Johnsen (2001) divided Onisimus into several provisional species groups (Table 1), based partly on biological data and partly on the results of his morphological comparisons and preliminary phylogenetic analyses. We will retain these groupings in this series of papers, but only as informal taxonomic groups. The primary aim of these works is to provide a revision and, as far as possible, thorough descriptions and illustrations of all nominal taxa within the genus. This first paper discusses the O. brevicaudatus- and O. sextonae-groups of species. Subsequent papers will treat the remaining species groups. At a later stage, a phylogenetic analysis of Onisimus and the closely related genera Menigrates Boeck, 1871 and Paralibrotus Stephensen, 1923 will be provided, but this can be done only after alpha taxonomy has been studied thoroughly. Thus, no diagnoses are given for the various groups here, only a short list of morphological features that are characteristic for each group. However, in order to facilitate consistent separation of these groups, a provisional key is provided. Two species, O. uschakovi and O. zenkevitchi, are treated as incertae sedis, as they are insufficiently described and figured. These two species of uncertain placement, as well as the nomen dubium O. punctatus, have been excluded from the provisional key. As indi- Table 1: Allocation of Onisimus species to provisional groups (modified after Johnsen 2001); in addition to the 22 species listed, O. punctatus is considered as a nomen dubium, O. uschakovi and O. zenkevitchi as incertae sedis (see text). brevicaudatus-group sextonae-group barentsi-group edwardsii-group normani-group litoralis-group O. affinis O. abyssi O. barentsi O. edwardsii O. normani O. birulai O. botkini O. leucopis O. krassini O. turgidus O. caspius O. brevicaudatus O. sextonae O. plautus O. glacialis O. caricus O. sibiricus O. litoralis O. derjugini O. simus O. nanseni O. platyceras

3 Vader & al.: Studies on Onisimus (Crustacea, Uristidae) I. 3 cated by Lowry and Stoddart (1993:169), O. uschakovi was described as having no mandibular molar, and thus possibly should be considered as not belonging to the genus Onisimus. Examination of the holotype of O. uschakovi by the present third author has revealed that all its mouthparts and uropods have been totally destroyed, leaving the question of the mandibular molar unanswered. However, the morphology of the remaining appendages agrees very well with general morphology in Onisimus, and hence does not support the suspicion that the species might be misplaced in this genus. Key to Onisimus species groups and related genera 1. Telson entire or weakly notched... 2 Telson clearly cleft (15-50%) Pereopod 1 simple... Paralibrotus Stephensen Pereopod 1 subchelate Urosomite 3 with small dorsal robust setae proximal to telson; antenna 1 accessory flagellum short ( times the length of primary flagellum); epimeral plates 2-3 posterodistally acute or with small tooth... litoralis-group Urosomite 3 without small dorsal robust setae proximal to telson; antenna 1 accessory flagellum long (more than 0.3 times the length of primary flagellum); epimeral plates 2-3 rounded or with moderately large tooth Pereopods 5-7 propodus anterior margin with paired long and short robust setae; pereopods 3-4 merus with medio-lateral row of setae... brevicaudatus-group Pereopods 5-7 propodus anterior margin with paired short robust setae only; pereopods 3-4 merus without mediolateral row of setae... sextonae-group 5. Uropod 2 inner ramus completely constricted... normani-group Uropod 2 inner ramus not constricted Pereopod 1 simple... Menigrates Boeck Pereopod 1 subchelate Pereopod 1 coxa rectangular, not expanded; cephalic lobe acute, with straight sides... 8 Pereopod 1 coxa slightly or clearly expanded ventrally; cephalic lobes subrounded, with convex sides Pereopod 5 coxa with clear posteroventral lobe, ischium with ventral margin shorter than that of merus... O. plautus (barentsi-group) Pereopod 5 coxa equilobate, ischium with ventral margin equal to that of merus... O. leucopis (sextonae-group) 9. Antenna 1 produced anterodistally (with nose )... barentsi-group Antenna 1 not produced anterodistally Maxilla 1 palp distomedial margin serrate... sextonae-group Maxilla 1 palp distomedial margin smooth... edwardsii-group Onisimus brevicaudatus-group Species included (5). Onisimus affinis Hansen, 1886 (= O. dubius Schellenberg, 1935, syn. n.), O. botkini Birula, 1897, O. brevicaudatus Hansen, 1887, O. caricus Hansen, 1887, and O. derjugini Gurjanova, Morphological characteristics. Cephalic lobe subrounded to rounded, antenna 1 peduncle article 1 without or with weakly developed nose. Mandibular molar rounded and weakly triturative. Maxilla 1 outer plate with setal teeth in 7/4 or 7/5 crown arrangement. Coxa 1 strongly expanded ventrally, coxa 4 with moderate posteroventral lobe. Pereopods 3 and 4 merus with mediolateral row of setae; propodus without setae along anterior margin, the posterior margin with paired simple setae. Pereopods 5-7 propodus with paired long and short robust setae. Telson entire or emarginate. Key to the species of the brevicaudatus-group 1. Cephalic lobe anteriorly rounded Cephalic lobe anteriorly angular and pointed... O. derjugini 2. Telson distally weakly emarginated Telson distally convex... O. brevicaudatus 3. Pereopod 2 dactylus shorter than palm... O. caricus - Pereopod 2 dactylus as long as palm... O. affinis / O. botkini (see text) Remarks The nominal taxon O. dubius Schellenberg here is considered a junior synonym of O. affinis. Onisimus botkini Birula possibly is another synonym of O. affinis, but for the time being is retained as a separate species. This mainly is because type material of O. botkini has not been available for examination, and some ecological differences (in salinity preference) seem to exist between the two taxa. Morphologically, they appear as almost identical. The four species O. affinis, O. botkini, O. brevicaudatus and O. caricus are all common and wide-spread scavengers of shallow waters in the Arctic (O. brevicaudatus and O. caricus were first found on dead dogs by the Dymphna expedition to the Kara Sea; Hansen 1887). These species are characterized by an entire or almost entire telson, strongly subchelate (to weakly parachelate) pereopods 1-2, and the presence of a medial row of setae on the merus of pereopods 3-4. Onisimus derjugini shares several of these characteristics and likewise has a wide Arctic distribution, but it has not been found in baited traps. Moreover, it shares

4 Vader & al.: Studies on Onisimus (Crustacea, Uristidae) I. 4 some morphological characteristics with the litoralisgroup (to be treated in a subsequent paper). It is treated in the brevicaudatus-group here due to similarities in the morphology of the mandible. Onisimus affinis Hansen, 1887 (Figs. 1-7) Onisimus affinis Hansen, 1887: 216, pl Brüggen (1909: 11, figs 6-9); Stephensen (1923: 47); Gurjanova (1951: 172, fig. 46). Onisimus dubius Schellenberg, 1935: 12, fig.1; syn. n. Gurjanova (1951: 173, fig. 47). Type locality. Kara Sea. Morphological characteristics. Telson entire. Epimeral plate 3 with posteroventral tooth. Uropod 2 inner ramus with more than 1 seta on outer margin. Pereopod 3 merus with medioventral row of setae. Pereopod 2 subchelate to weakly parachelate. Material examined. Paratype (ZMC 3205): immature male 10mm. Additional material: ZMC 3206, female, 18mm, N,19 W, Kara Sea; ZMO 1009, Kara Sea, 5 spm; ZMO 1009, Kara Sea, 5 spm; ZMB 27/41712, male, 13mm, 46 40'N,100 40'E; SMNH 6510, 69 32'N,177 41'E, 12 ftm; SMNH 6670, about 100 spm; SMNH 6670, Det: O.plautus, female, 22mm, 8-9 ftm, N,66 E, Kara Sea; SMNH 6670, female, 22mm, adult, det: O. plautus. Nordenskiölds Exp. 1876, Kara Sea N,66 E, 8-9 fathoms, sand; USNM , Kara Sea, 5 spm; USNM , Point Barrow base, Alaska, 1 spm; USNM , Cape Barease Warren, 1 spm; USNM Acc.no , Point Barrow base, Alaska, 4 spm; USNM Acc.no , Point Barrow, Alaska, 2 spm; USNM Acc.no , Point Barrow, Alaska, 3 spm. Distribution. Owing to the uncertain status of O. botkini, there remains much uncertainty about the exact distribution of O. affinis. For example, although Gurjanova (1962) emphatically keeps the two taxa apart, her later (1985) map in the Atlas Arktiki no longer mentions O. botkini, and apparently all records of the two taxa are mapped as O. affinis (whereas O. dubius is mapped separately). Apparently O. affinis has a circumarctic distribution, mostly in quite shallow and often slightly brackish waters. The species has been recorded from Alaska (Shoemaker 1920; many later authors), the Canadian Arctic (Percy 1975), Labrador (Dunbar 1954), E Greenland (Stephensen 1937, 1944), Jan Mayen (Stephensen 1923), Svalbard (TMU), Novaya Zemlya (Gurjanova 1985), the Kara Sea (Hansen 1887; Gurjanova 1951), the Laptev Sea (Golikov 1990), and the East Siberian Sea (Golikov and Tzvetkova 1994). The southernmost records are those mapped by Gurjanova (1985) from SE Greenland. Apparently, the species is not present in the large collections from the St Lawrence area (Brunel et al. 1998) and the Barents Sea area (Bryazgin 1997). Under the name O. dubius this species has been recorded from E Greenland (Schellenberg, 1935), the Kara Sea (Gurjanova 1951), the Laptev Sea (Golikov 1990), the East Siberian Sea (Golikov and Tzvetkova 1994), and the Canadian Arctic (Legezynska et al. 2000). Biology. Most records of O. affinis are from shallow water (5-40 m), although intertidally the species often seems to be replaced by O. litoralis. Occasionally the species is recorded from much deeper water ( m; Stephensen 1923). Onisimus affinis is readily caught in baited traps (Percy 1979; Busdosh et al. 1982), but these authors still considered the species mainly to be a benthic detritivore. They also found that during the winter, large numbers congregated at the ice-water interface. Onisimus affinis is often found in slightly brackish water. Stephensen (1923) remarked on the large size and low numbers of the eggs in this species. Mac- Ginitie (1955) described in vivo colouration in detail. Description Head and body. Head as long as pereon 1. Cephalic lobe broadly triangular; distally subrounded. Eyes oval, red. Urosomite 1 with very slight dorsal depression. Epimeral plate 1 without posteroventral corner. Epimeral plate 2 with ventral margin slightly concave and without posteroventral tooth. Epimeral plate 3 anteroventral corner rounded, ventral margin convex, with moderately produced posteroventral subacute tooth. Antennae. Antenna 1 as long as head and two body segments; peduncle article 1 not produced into a nose anterodistally; accessory flagellum 0.35 times primary flagellum, 6-articulate; primary flagellum times as long as peduncle, 17-articulate, article 1 as long as next 3 articles, callynophore present in males and females, calceoli present in males, absent in females. Antenna 2 length 1.2 times antenna 1; peduncle article 4 longer than article 5; flagellum 19-articulate, calceoli present in males, absent in females. Mouthparts. Epistome convex; Labrum straight, not in front of epistome. Mandible incisors with convex margins; left lacinia mobilis present; 2-3 accessory setae present on left and right mandible; molar rounded and weakly triturative; palp attached opposite to molar; palp article 1 with 5 setae; palp article 2 with 31 distoventral and 1 proxiventral setae; palp article 3 with 33 distoventral setae. Maxilla 1 inner plate with 2 pappose setae; outer plate with ST in a 7/4 crown arrangement; palp with 8 short robust setae distally and 1 distolateral seta, distomedial margin smooth. Maxilliped inner plate apically with 3 nodular setae, inner and medial setal rows present and almost continuous, setae pappopectinate, distal setae reduced (1-2 short simple setae); outer

5 Vader & al.: Studies on Onisimus (Crustacea, Uristidae) I. 5 plate subovate, distal group of setae with 4 long robust setae; outer row with short robust setae, distally increasing in length; inner row present, with short simple setae; palp 4-articulate; unguis present on dactylus. Pereopods. Pereopod 1 subchelate; coxa with anterior margin concave, anteroventral corner clearly produced and rounded; basis length times breadth; setation along both anterior and posterior margin; ischium length about 2 times breadth, slightly longer than merus; merus length subequal to carpus; propodus times length of carpus, rectangular, length times breadth, palm oblique, straight and serrate, slightly convex and defined by 2 slender robust setae; dactylus longer than palm, accessory tooth present, cuticular teeth along ventral margin. Pereopod 2 weakly parachelate; length of propodus times carpus, rectangular, length 1.8 times breadth; dactylus medium-sized, not as long as palm. Pereopod 3 merus produced anteriorly; mediolateral row of setae present; propodus posterior margin with 2 small apical robust setae and 9 pairs of single setae; length of dactylus 0.5x propodus. Pereopod 4 coxa with moderate posteroventral lobe. Pereopod 5 coxa almost equilobate (posterior lobe very slightly produced ventrally). Pereopod 6 coxa with moderately produced posterior lobe. Pereopod 7 basis posteroventral margin almost straight; merus not expanded; propodus anterior margin medially with 4 groups of paired or single, long and short robust setae, 2 apical short robust setae. Gills present on pereopods 2-6, with accessory lobe on pereopods 5 and 6; oostegites present on pereopods 2-5. Uropods and telson. Uropod 1 peduncle slightly longer than rami; rami subequal; peduncle outer margin with 3 short robust setae distally; inner margin with 5 long robust setae; outer ramus with 6 robust setae on outer margin; inner ramus with 7 robust setae on inner margin and 3 robust setae on outer margin. Uropod 2 rami longer than peduncle; peduncle outer margin with 12 robust setae; inner margin with 1 apical robust seta; rami subequal; outer ramus with 5 robust setae on outer margin; inner ramus not constricted, with 5 robust setae on inner margin and 1 robust seta on outer margin. Uropod 3 outer ramus slightly longer than peduncle; peduncle with 3 robust setae apically on inner margin and 2 medioapical robust setae; outer ramus 2-articulate, times longer than inner ramus, with 3 robust setae on outer margin and 1 robust seta on inner margin; inner ramus with 1 robust seta on inner margin and 3 robust setae on outer margin. Telson emarginate, length 1.1 times breadth; 2 dorsal setae medially on each side; 2 pairs of apical setae. Remarks Type material of O. affinis and O. dubius was examined, in addition to numerous specimens from other localities. As the holotype of O. affinis is an immature specimen, illustrations were prepared from topotypic material collected in the Kara Sea. Figure 4 shows structures of a syntype of O. dubius. Onisimus botkini Birula, 1897 Onesimus botkini Birula, 1897: 105. Brüggen (1909: 7, pl. 2:20-25); Shoemaker (1920: 4, figs 1-2); Gurjanova (1951: 174, fig.48); Gurjanova (1962: 62). Type locality: Kara Sea. Material examined. ZMO 1010, Kara Sea, 2 spm.; Akvaplan, male, 13 mm. ST Kara Sea; Zool. Mus. St. Petersburg, N12/31949, male, 9 mm, Bering Sea; TMU 10007, Eskimo Lakes, NWT. 4 spm; USNM , Kara Sea, 2 spm.; USNM 54347, Acc. no 64791, Demarcation Point, Alaska; USNM 54348, Acc.no 64791, Demarcation Point, Alaska, 20 spm.; USNM 54350, Collinson Point, Alaska, 3 spm Remarks. Gurjanova (1951, 1962) noted that the two closely related species O. affinis and O. botkini could be separated based on the morphology especially of epimeral plate 3, but also on the second pereopod and the rami of the second uropod. Variation in these characters can be observed indeed in material from the Kara Sea (type locality for both species), but intermediate forms exist for all these character states both in material from the Kara Sea and from elsewhere, indicating that O. affinis and O. botkini possibly should be considered as synonymous. Moreover, specimens identified as O. botkini by Dr Gurjanova are identical to O. affinis. However, as it has not been possible yet to examine type specimens of O. botkini, for the time being we tentatively retain O. botkini as a separate species. As a result, at present it is only possible to separate the two species on ecological preferences: Gurjanova (1951: 174) noted that, although the two species often occur within the same area, they are never caught in the same sample. She provides an example from the estuary of the River Ob, in which the two species never coexist within the same salinity zones. Onisimus affinis was never caught in areas with salinities below ppt, whereas O. botkini was restricted to waters in which salinity exceeded 5-7 ppt. Onisimus brevicaudatus Hansen, 1887 (Figs. 8-11) Onisimus brevicaudatus Hansen, 1887: 216, pl Stephensen (1935: 40); Gurjanova (1951: 169, fig.43). Type locality: Kara Sea (Hansen, 1887). Morphological characteristics. Telson entire and rounded. Outer ramus of uropods 1 and 2 with robust setae present on inner margin. Female pereopod 2 propodus rectangular with straight palm.

6 Vader & al.: Studies on Onisimus (Crustacea, Uristidae) I. 6 Material examined. Syntypes (ZMC): female 17 mm, Kara Sea; male 15 mm, Kara Sea. Additional material: CMNC , female, 15 mm, adult, N,76 17 W. Richmond Gulf, Canada; SMNH 6671, N,61 W, 90 ftm, 6/7-1876, 1 spm. Kara Sea; TMU 9863, female, 15 mm, Storfjord, Spitsbergen; TMU 9864, Duvefjord, Spitsbergen, about 100 spm; TMU 12487, Storegga, Norway, 812 m, in fish stomach,1 spm. Distribution. Onisimus brevicaudatus was described from the Kara Sea (Hansen 1887). The species seems to be most common in Russian waters. Bryazgin (1997) recorded it as common in the northern parts of the Barents Sea, and there also are many records from the Kara Sea (cf. Gurjanova 1985) and the Laptev Sea (Gurjanova 1985; Golikov 1990). Further east there are fewer records: neither Gurjanova (1962) nor Golikov and Tzvetkova (1994) note the species from the Siberian Far East. There also are only few and isolated records from the Nearctic: Shoemaker (1920) found specimens in seal stomachs north of Alaska; we have seen one specimen from the Canadian Arctic (Johnsen 2001); and Legezynska et al. (2000) collected a single specimen from north-eastern Greenland. Also around Hornsund in S Svalbard O. brevicaudatus is scarce (cf. Weslawski and Legezynska 2002), but in the collections of Tromsø Museum there are many samples from south-eastern and north-eastern Svalbard, in agreement with Bryazgin s data from the Barents Sea. Somewhat unexpectedly, the species recently was collected also from Cottunculus stomachs in the deep Norwegian Sea off western Norway (TMU). Biology. The type material of O. brevicaudatus was collected from dead dogs (Hansen 1887), and also later this species has been collected regularly from baited traps. It usually is collected in fully saline and not very shallow water: Bryazgin (1997) gives depths of m from the northern Barents Sea, and the Svalbard records in our collections are from similar depths, as are the Kara Sea records of Stebbing (1894) and Brüggen (1909). The material from off the Norwegian coast was collected from 812m depth. Description Head and body. Body coloured pinkish dorsally, otherwise white. Head slightly longer than first pereon segment; cephalic lobe broadly triangular, moderately produced, distally subacute; eyes red and oval. Epimeral plate 1 anteroventral corner weakly produced and subangular, ventral margin weakly convex; posteroventral corner not clearly marked and rounded. Epimeral plate 2 anteroventral corner rounded, ventral margin weakly concave, posteroventral corner acute with a small tooth, posterior margin straight. Epimeral plate 3 anteroventral corner rounded, ventral margin convex; posteroventral corner produced into a strong, acute tooth, posterior margin weakly convex. Urosomite 1 with saddle-like depression dorsally. Antennae. Antenna 1 as long as head and following pereon segment (the male with antenna 1 as long as head and 2 pereon segments); peduncle not produced anterodorsally; accessory flagellum more than half the length of primary flagellum (in male 0.4 times primary flagellum), 5-articulate; primary flagellum length 1.2 times peduncle, 10-articulate; article 1 as long as the following two articles; callynophore present in males and females; calceoli present in males, absent in females. Antenna 2 length about 1.2 times the length of antenna 1; peduncle article 4 slightly longer than article 5; flagellum 14-articulate; calceoli present in males, absent in females. Mouthparts. Epistome convex. Labrum slightly convex, in front of epistome. Labium with 1 apical robust seta on each lobe (broken off in the specimen figured). Mandible incisors with convex margin; left lacinia mobilis present; accessory row of setae present on left and right mandible, 3 setae; molar circular with triturative surface; palp article 1 longer than broad; article 2 longer than 3, 27 setae on distoventral margin; article 3 with 32 setae on distoventral margin. Maxilla 1 inner plate with 2 pappose setae; outer plate with ST in a 7/4-crown arrangement; palp large, 2-articulate, distally with 7 robust and 1 simple setae; distomedial margin smooth. Maxilliped inner plate distally with 3 nodular setae; inner and medial groups of setae almost continuous, setae pappose; distal group present, 1 simple seta; outer plate subovate, without subapical notch; distal group of setae present, 1 long robust seta; outer row present, setae very short, robust; inner row present, setae simple; palp 4-articulate; unguis present on dactylus. Pereopods. Pereopod 1 subchelate; coxa anterior margin slightly concave, anteroventral corner produced and rounded; basis length 2 times breadth, strong setation along anterior and weak setation along posterior margin; ischium posterior margin longer than broad; merus subequal to ischium; carpus slightly longer than merus; propodus longer than carpus, rectangular, length more than 2 times breadth, palm oblique and straight, serrate, weakly defined by 2 to 3 robust setae; dactylus as long as palm, accessory tooth present, cuticular teeth along posterior margin. Pereopod 2 subchelate; coxa rectangular with notch in posterodistal corner; ischium longer than merus; merus about half the length of carpus; propodus about half the length of carpus; propodus subovate, length 1.85 times breadth, distal margin dilated in the middle; dactylus medially placed on palm; dactylus as long as palm. Pereopod 3 coxa with notch in posterodistal corner; merus with

7 Vader & al.: Studies on Onisimus (Crustacea, Uristidae) I. 7 mediolateral row of setae present; propodus posterior margin with 2 apical short robust setae and 12 groups of paired or single setae; dactylus long and slender. Pereopod 4 coxa posteroventral lobe deep and moderately produced. Pereopod 5 coxa nearly equilobate (the posterior lobe slightly produced ventrally). Pereopod 6 coxa small, lobate posteriorly. Pereopod 7 basis expanded posteriorly with crenate posterior margin, convex, posteroventral corner rounded; merus not expanded posterodistally; propodus anterior margin with 2 apical short robust setae and 4 groups of long paired or single robust setae; dactylus short and slender. Gills on pereopods 2-6, with extra lobe on pereopods 5 and 6; oostegites on pereopods 2-5. Uropods and telson. Uropod 1 peduncle longer than rami, peduncle outer margin with 12 robust setae, inner margin with 6 robust setae; rami of equal length; outer ramus with 10 long robust setae on outer margin and 4 robust setae on inner margin; inner ramus with 13 long robust setae on inner margin and 7 robust setae on outer margin. Uropod 2 peduncle broad, shorter than rami; peduncle outer margin with 15 long robust setae; inner margin with 1 apical robust seta; rami of equal length; outer ramus with 9 long medioproximal robust setae on outer margin and 3 long robust setae medially on inner margin; inner ramus without constriction, with 9 long mediodistal robust setae on inner margin and 3 long robust setae on outer margin. Uropod 3 peduncle as long as rami; peduncle with 1 apical robust seta on inner margin; outer ramus longer than inner ramus, 2- articulate; 5 robust setae on inner margin; inner ramus with 5 robust setae on inner margin. Telson entire, as long as broad, distal margin straight to slightly convex, 2 dorsolateral setae present on each side, distally with 2 pairs of small robust setae (broken off in the figured specimen). Variation. The syntype (female) from the Kara Sea differs from the adult females found in Duvefjord (Svalbard), Storegga outside Norway (812m), and Richmond Gulf (Canada) in the morphology of the propodus on pereopod 2. No differences were found between males. Remarks Hansen (1887), in his type description, gives the following characteristics: antenna to 11-articulate in adult female, 16- to 17-articulate in adult male, accessory flagellum 5-articulate in both sexes; antenna to 15-articulate in female, 19- to 20-articulate in male; calceoli present on both antennae in male; male gnathopod 2 propodus shape different from that of female, male propodus triangular. Specimens from Duvefjord fit with Hansen s typedescription quite well. A minor disagreement concerns the reported difference in male vs. female shape of the pereopod 2 propodus. No such difference has been observed in the Svalbard material, as there is in the type material from the Kara Sea (Fig. 8). Otherwise, females appeared to possess somewhat longer and stouter antennae than males, but the ratio between them seems to be the same for both sexes. The males have antenna 1 primary flagellum article 1 as long as the next 3-4 articles, whereas in females it is as long as the next 2 articles. Onisimus caricus Hansen, 1887 (Figs ) Onisimus caricus Hansen, 1887: 214, pl Stephensen (1935: 41); Gurjanova (1951: 171, fig. 45). Type locality: Kara Sea. Morphological characteristics. Pereopod 2 propodus subtriangular, distally widening, palm transverse and straight to slightly concave, dactylus powerful and hook-like, shorter than palm. Cephalic lobe rounded. Pereopods 3 and 4 merus and carpus with mediolateral row of setae. Pereopods 5 and 6 coxa not lobate. Uropod 1 inner ramus with 5-6 robust setae present on outer margin. Telson emarginate. Material examined. Syntypes (ZMC): female adult 22 mm, Kara Sea; male adult 24 mm, Kara Sea, 4 spm. Additional material: ZMB 10320, female, 20 mm, Arctic Ocean 24/6-1901, 18 m; ZMB 10320, male, 11 mm, Arctic Ocean 24/6-1901, 18m. Distribution. Onisimus caricus was described from the Kara Sea after the Dymphna expedition (Hansen 1887), and also has a circumarctic distribution, with most records in the Palaearctic (see map in Gurjanova 1985). Somewhat unexpectedly, the species is not present in Bryazgin s (1997) extensive collections from the Barents Sea area, but it does occur, albeit not in very large numbers, in Hornsund, south-western Svalbard (Weslawski 1990), and Legezynska et al.(2000) collected it from baited traps in Svalbard, Franz Joseph Land and Ellesmere Island in the Canadian Arctic. In the Svalbard collections at Tromsø Museum O. caricus unexpectedly is much less often found than O. brevicaudatus. There are records from the Laptev Sea (Gurjanova 1985; Golikov 1990) and the East Siberian Sea (Gurjanova 1985), and Gurjanova (1985) also maps single records from the Beaufort Sea north of Alaska, and from the Norwegian Sea. Biology. Onisimus caricus is a well-known scavenger. As in the case of O. brevicaudatus, the type material was collected from dead dogs (Hansen 1887), and much of the later material has also been collected in baited traps. Most of the records of O. caricus in Siberian waters stem from waters somewhat closer to the respective coasts than in O. brevicaudatus (see map in Gurjanova 1985), but the species also has been collec-

8 Vader & al.: Studies on Onisimus (Crustacea, Uristidae) I. 8 ted at depths down to 175 m (Legezynska et al. 2000). Some biological data on this species are provided by Legezynska (2001) and Weslawski and Legezynska (2002). Description Head and body. Head longer than pereon segment 1; cephalic lobe broadly triangular, distally rounded; eyes oval, red (absent in alcohol). Epimeral plate 1 anteroventral corner weakly produced and subangular, no posteroventral corner. Epimeral plate 2 anteroventral corner rounded, ventral margin straight, posteroventral corner subangular without tooth, posterior margin straight. Epimeral plate 3 anteroventral corner rounded, ventral margin weakly convex; posteroventral corner produced into a strong, blunt, upturned tooth. Urosomite 1 depressed dorsally. Antennae. Antenna times as long as pereon segment 1; peduncle article 1 longer than broad, not produced anterodorsally; accessory flagellum 6-articulate, length 0.4 times primary flagellum; primary flagellum 16-articulate and 1.5 times the length of peduncle, article 1 as long as the next 3 articles; callynophore present in males and females; calceoli present in males, absent in females. Antenna 2 length 1.3 times antenna 1; peduncle article 4 longer than 5; flagellum 8-articulate; calceoli absent in females. Mouthparts. Epistome slightly convex. Labrum straight, not in front of epistome. Mandible incisors with convex margin; left lacinia mobilis present; accessory row of setae present on left and right mandible, 3 setae; molar present, circular (not oval) with triturating surface; palp article 1 longer than broad, with 6 long setae; article 2 longer than article 3, with distoventral setae; article 3 with distoventral setae. Maxilla 1 inner plate with 2 pappose setae; outer plate with ST in a 7/4 crown arrangement; palp large, 2-articulate, distally with 8 robust setae, distal simple setae absent; distomedial margin smooth. Maxilliped inner plate distally with 5 nodular setae; inner and medial groups of setae almost continuous, setae pappose; distal group present, 1 simple seta; outer plate subovate, without subapical notch; distal group of setae present, 3 long robust setae; outer row present, setae very short, robust, distally increasing in length; inner row present, setae simple; palp 4-articulate; unguis present on dactylus. Pereopods. Pereopod 1 subchelate; coxa anterior margin slightly concave, anteroventral corner produced and rounded, ventral margin straight to weakly convex, posterior margin straight; basis length about 2.5 times breadth, heavily setose along anterior and posterior margins; ischium posterior margin twice as long as broad, posterior margin with 5 groups of long setae, subequal or slightly longer than merus; merus subequal to carpus; propodus longer than carpus, rectangular; length about 2.5 times breadth, anterior margin convex, posterior margin concave; palm oblique and convex, serrate, posterodistal corner of palm not clearly defined, produced and rounded with 5 slender robust setae; dactylus as long as palm, accessory tooth present, ventral margin with serrations. Pereopod 2 subchelate; basis with setae along anterior margin; carpus 1.5 times merus; propodus triangular, distally widening, length 1.3 times breadth; palm straight to weakly concave, smooth (setae present); dactylus medially placed on palm, shorter than palm, strongly hooked, posterior margin smooth. Pereopod 3 merus expanded anteriorly; mediolateral row of setae present; propodus anterior margin without row of setae. Pereopod 4 coxa anterior margin convex, posteroventral lobe deep and strong. Pereopod 5 coxa equilobate. Pereopod 6 coxa small, not lobate anteriorly. Pereopod 7 basis expanded posteriorly with minutely crenate convex posterior margin, posteroventral corner acute, robust setae along whole anterior margin; merus not expanded posterodistally; propodus anterior margin with 5 groups long and short robust setae; dactylus long, slender. Gills on pereopods 2-6, on pereopods 5 and 6 with accessory lobe; oostegites on pereopods 2-5. Uropods and telson. Uropod 1 peduncle longer than rami, outer margin with 5 robust setae, inner margin with 10 robust setae; outer ramus with 8 robust setae on outer margin; without setae on inner margin; inner ramus with 8 long robust setae on inner margin; 5 robust setae on outer margin. Uropod 2 peduncle shorter than rami, outer margin with 12 robust setae, inner margin with 1 apical robust seta; rami of equal length; outer ramus with 7 robust setae medially on outer margin, inner margin without robust setae; inner ramus without constriction, with 6 robust setae on inner margin, outer margin with 2 robust setae. Uropod 3 peduncle with 3 apical robust setae on inner margin; outer ramus longer than inner ramus, 2-articulate; outer ramus with 3 medial robust setae on outer margin, 1 robust seta on inner margin; inner ramus with 3 robust setae on outer margin distal particle, 1 robust seta on inner margin. Telson emarginate, weakly longer than broad; 2 mediodorsal simple setae and distally 2 pairs of simple setae. Male (2.4 cm, adult, syntype). Antenna 1 as long as the head and 4 pereon segments; accessory flagellum times primary flagellum, 5-articulate; primary flagellum-32 articulate; calceoli present. Antenna times longer than antenna 1; peduncle article 5 with 5 ventral groups of setae; flagellum 36-articulate; calceoli present. No sexual dimorphism on pereopods 1 and 2. Uropod 3 outer ramus with plumose setae present on inner margin.

9 Vader & al.: Studies on Onisimus (Crustacea, Uristidae) I. 9 Onisimus derjugini Gurjanova, 1929 (Figs ) Onisimus derjugini Gurjanova 1929: 312, fig. 3. Stephensen (1935; 40); Gurjanova (1951: 170, fig. 44). Type locality. East and West coasts of Novaja Zemlya, 12 m. Morphological characteristics. Cephalic lobe distally acute with concave margins. Antenna 1 peduncle article 1 with short nose. Mandible palp article 1 with long setae. Maxilla 1 outer plate with setal teeth in 7/5 crown arrangement. Coxa pereopods 5 and 6 greatly produced posteroventrally. Telson weakly emarginate. Material examined. ZMC 3204, female, 16 mm, Okhotsk; ZMB 23652, male, 17 mm, Laptev sea; SMNH 6511, female, 20 mm, Pitlebay Vega; SMNH 6546, juli/1875. N.Semlya exp, S.Gåskap, 3 spm. TMU 9932, female, N, E; USNM Det: O. affinis, Cape Lisburne, Kiska, Alaska, 1 spm; USNM Acc.no , Point Barrow, Alaska, 1 spm; USNM Acc.no , Point Barrow, Alaska, 1 spm. Distribution. Onisimus derjugini was described from the east and west coasts of Novaya Zemlya (Gurjanova 1929). It has been collected from the Kara, East Siberian and Chukotsk seas (Gurjanova 1962, 1985; Golikov 1990; Golikov and Tzvetkova 1994) and, almost uniquely for this section of Onisimus, also occurs south of the Bering Straits (Gurjanova 1962, 1985); the southernmost record is from 58 N (Gurjanova 1934)! The species clearly also occurs around Point Barrow in Alaska, where it was collected by MacGinitie (1955), although that author as well as Shoemaker (1955) mixed it up with O. affinis (specimens from the USNM, revised by Johnsen 2001). Gurjanova (1962) reports the species from the Gulf of St. Lawrence, but it is not recorded from that area in the very complete catalogue of its marine fauna by Brunel et al. (1998). Biology. Onisimus derjugini is a typical shallowwater species of soft bottoms, usually found at depths shallower than 20 m, although it does occur in somewhat deeper water south of the Bering Straits. We have not found any records from baited traps. Description Head and body. Head length slightly longer than first pereon segment; cephalic lobe triangular, moderately produced, distally subacute, concave margins; eyes yellow-brown in alcohol, oval. Epimeral plate 1 anteroventral corner weakly produced and subangular, ventral and posterior margin evenly rounded, no posteroventral corner. Epimeral plate 2 anteroventral and posteroventral corners rounded, posterior margin weakly concave. Epimeral plate 3 anteroventral corner rounded, ventral margin weakly convex, posteroventral corner produced into a strong, acute tooth. Urosomite 1 long, 4 times the length of urosomite 2, dorsally with saddle-like depression. Antennae. Antenna 1 as long as cephalon and the first two pereon segments; peduncle article 1 produced anterodorsally on inner margin (nose), partly covering peduncle article 2; accessory flagellum length 0.6 times primary flagellum, 5-articulate; primary flagellum 15-articulate, article 1 as long as proceeding 5 articles; callynophore present in males and females; calceoli present in males, absent in females. Antenna 2 length 1.4 times antenna 1; peduncle article 4 longer than 5; article 5 with 5 groups of long setae ventrally and 2 groups distally; flagellum 17-articulate; calceoli absent in females. Mouthparts. Epistome convex. Labrum straight, not in front of epistome. Labium with 1 apical robust seta on each lobe. Mandible incisors with convex margin; left lacinia mobilis present; accessory row of setae present on left and right mandible, 3 setae; molar rounded with triturating surface; palp article 1 longer than broad, article 1 with 8-10 long and short setae; article 2 with 9 medioventral setae and 25 distoventral; article 3 with 30 distoventral setae. Maxilla 1 inner plate with 2 pappose setae; outer plate with ST in a 7/5-crown arrangement; palp large, 2-articulate, 8 distal robust setae, distally without simple setae, distomedial margin smooth. Maxilliped inner plate with 3 nodular setae distally; inner and medial groups of setae almost continuous, setae pappose; distal group present, 1 simple seta; outer plate subovate, without subapical notch; distal group of setae present, 1 robust seta; outer row with short robust setae, distally increasing in length; inner row present, setae short and simple; palp 4-articulate, dactylus very slender, unguis present. Pereopods. Pereopod 1 subchelate; coxa anteroventral corner not produced, rounded; basis length times breadth, setation along anterior and posterior margin; ischium posterior margin longer than breadth; merus as long as ischium; carpus longer than merus, as long as propodus; propodus rectangular, twice as long as broad, margins subparallel; palm clearly defined with 2 robust setae, oblique, straight and serrate; dactylus as long as palm, accessory tooth present, cuticular teeth along posterior margin. Pereopod 2 subchelate; merus 0.6 times carpus; propodus time carpus, subrectangular, slightly convex margins; palm transverse and slightly convex; dactylus shorter than palm, medium sized. Pereopod 3 merus strongly produced anteriorly and slightly expanded, mediolateral row of setae present; propodus with setae along anterior margin; dactylus long and slender. Pereopod 4 coxa anterior margin slightly convex, moderate posteroventral lobe. Pereopod 5 coxa asymmetrically bilobate, posterior lobe strongly produced ventrally. Pereopod 6

10 Vader & al.: Studies on Onisimus (Crustacea, Uristidae) I. 10 coxa small, strongly lobate posteriorly; basis slightly expanded posteriorly with minutely crenate margin; propodus much longer than propodus on pereopod 5 and 7. Pereopod 7 basis expanded posteriorly with minutely crenate posterior margin; merus not expanded posterodistally; propodus anterior margin with 2 apical robust setae and 3 groups of paired or single robust setae; dactylus long, slender. Gills on pereopods 2-6. Uropods and telson. Uropod 1 peduncle shorter than rami, outer margin with 9 robust setae, inner margin with 10 robust setae; outer ramus longer than inner ramus, 6 long robust setae on outer margin; inner ramus with 6 long robust setae on inner margin. Uropod 2 peduncle shorter than rami, outer margin with 8 long setae and 1 apical robust seta, inner margin with 1 apical robust seta; outer ramus with 7 long robust setae on outer margin; inner ramus without constriction, without setae. Uropod 3 peduncle shorter than rami, 4 apical robust setae on inner margin, and 4 medioapical robust setae; outer ramus as long as inner, 2-articulate; 2 robust setae on outer margin, 2 robust setae on inner margin; inner ramus without setae. Telson entire, weakly emarginate, broader than long, distally with 2 robust setae on each side, 2 dorsolateral groups of 2 setae each. Remarks The placement of O. derjugini within the genus Onisimus is not definite before a phylogenetic analysis of the entire genus is carried out. However, the strong and acute tooth on the third epimeral plate and the morphology of the first pereopod indicate a close relationship with the brevicaudatus-group. Onisimus sextonae-group Species included (3). Onisimus abyssi Oldevig, 1959, O. leucopis (G.O. Sars, 1879), O. sextonae Chevreux, Morphological characteristics of the group. Cephalic lobe anteriorly triangular. Maxilla 1 palp distomedial margin serrate, outer plate with setal teeth in 7/4 crown arrangement. Mandibular molar oval and weakly triturative. Pereopod 4 coxa posteroventral lobe weakly produced. Telson distally weakly cleft. Key to the species of the sextonae-group 1. Eyes absent or weakly developed Eyes well developed... O. leucopis 2. Pereopod 2 palm distally concave, cephalic lobe triangular and pointed... O. sextonae - Pereopod 2 palm distally straight, cephalic lobe triangular and rounded... O. abyssi Onisimus abyssi Oldevig, 1959 (Figs ) Onisimus abyssi Oldevig, 1959: 8, figs 1-5 (p. 8) Type locality. Greenland Sea. Morphological characteristics. Telson weakly cleft. Epimeral plate 3 with posteroventral tooth. Coxa 1 expanded. Pereopod 1 propodus strong, dactylus longer than palm. Pereopod 2 propodus subrectangular. Material examined. Syntypes: SMNH 2342 (figured) male 15 mm, Svenskadjupet, 77 39'N, 1 17'E, 3200 m, Spitsbergen Exp. 27/7-1898; SMNH 2342, female 15 mm, same locality. Distribution. Only known from the type material from the Greenland basin. Biology. Deep sea (3200 m), collected in baited trap. Description Head and body. Head as long as pereon segment 1, cephalic lobe broadly triangular, moderately produced and distally rounded, dorsal margin straight, ventral margin convex; eyes absent in alcohol. Epimeral plate 1 anteroventral corner weakly produced and subangular. Epimeral plate 2 anteroventral corner rounded, ventral margin weakly concave, posteroventral corner acute. Epimeral plate 3 anteroventral corner rounded, ventral margin convex, posteroventral corner produced. Urosomite 1 with slight dorsal depression but no carina, no robust setae ahead of telson. Antennae. Antenna 1 as long as cephalon and next two pereon segments; peduncle longer than head, article 1 not produced anterodorsally; accessory flagellum length 0.6 times primary flagellum, 7-articulate; primary flagellum1.5 times longer than peduncle, 19- articulate; callynophore present in males and females; calceoli present in males, absent in females. Antenna 2 length about 1.5 times antenna 1 in males; peduncle article 4 slightly longer than article 5; flagellum 25-articulate; calceoli present in males, absent in females. Mouthparts. Epistome convex. Labrum slightly convex and slightly in front of epistome. Labium with 1 apical robust seta on each lobe. Mandible incisors with convex margin; left lacinia mobilis present; accessory row of setae present, 3 slender robust setae; molar oval with weakly triturating surface; palp attached opposite to molar, article 1 longer than broad, without setae; article 2 longer than 3, with 32 distoventral setae and 3-4 dorsomedial setae; article 3 with 39 distoventral setae. Maxilla 1 inner plate with 2 pappose setae; outer plate with ST in a 7/4 crown-arrangement; palp large and 2-articulate, distally with 6 robust setae, 1 simple seta present on distolateral corner (not visible on figure), distomedial margin with one large serration. Maxilliped inner plate with 4 nodular setae distally; inner and medial groups of setae almost continuous, setae pappose; distal group present, 1 simple seta; outer plate subovate, without subapical notch; distal group of se-