Stegocephalopsis Schellenberg, 1925

Vader, Berge Wim, 2001, North Paci ® c species of the amphipod (Crustacea) family Stegocephalidae, with description of one new species and redescription of another, Journal of Natural History 35, pp. 985-1000 : 989-994

Stegocephalopsis Schellenberg

Stegocephalopsis Schellenberg, 1925: 200 .

Type species. Cancer ampulla Phipps, 1774 .

Species. Stegocephalopsis ampulla ( Phipps, 1774) , S. latus (Haswell, 1879) , S. mamillidacta Moore, 1992 , S. paci W ca (Bulycheva, 1952).

Species found in the area. Stegocephalopsis ampulla , S. mamillidacta and S. paci W ca.

Remarks. The present genus has, until now, been used as a`catch-all’ genus into which all uncertain stegocephalid species possessing a gaping and geniculate maxilla were placed. Thus, Barnard and Karaman (1991) listed six species ( S. ampulla , S. katalia (Barnard, 1962) , S. latus , S. paci W ca, S. vanhoeOEeni (Schellenberg, 1926) and S. vegae Oldevig, 1959 ) as belonging to this genus, of which ®ve were labelled`doubtful’. Of the six species listed above, two have been transferred ( S. katalia to Stegocephalina Stephensen, 1925 (see Berge and Vader, 1997b)), and recently S. vanhoeOEeni to Phippsia Stebbing, 1906 (see Berge and Vader, in press)), and Stegocephalopsis vegae is herein put into synonomy with S. ampulla . The two remaining`doubtful ’ species, S. latus and S. paci W ca (see above), are indeed doubtful, as they appear to be more closely related to the Phippsia ± Tetradeion complex (see Berge and Vader, in press.) However, as material of these two relatively poorly described species has been inaccessible, they are retained, for the moment, as belonging to Stegocephalopsis .

The two remaining species in the genus, S. ampulla and S. mamillidacta , do not appear to be closely related, as they show signi®cant diOEerences in some important characters, mainly maxilla 1 and 2, and the maxilliped (see remarks under S. ampulla ).

Stegocephalopsi s ampulla ( Phipps, 1774) ( Figures 2 ±4) Cancer ampulla Phipps, 1774 .

Stegocephalopsis ampulla: BruÈggen, 1909 .

Stegocephalopsis ampulla: Gurjanova, 1951, 1962 .

Stegocephalopsis vegae: Oldevig, 1959 , new synonymy.

Material examined. CRU 2090:`Godthaab’ Exp. st. 107, one female ~ 50 mm, 15 August 1928, 76 ss 25 ¾ N, 69 ss 38 ¾ W, 165 m. CRU 2091:`Godthaab ’ Exp. st. 99, two immature, 10±15 mm, 8 August 1928, 78 ss 14 ¾ N, 74 ss 10 ¾ W, 672 m.

Zoological Museum, Hamburg: K 22804 , Spitsbergen , two specimens ; K 22809 , Greenland, three specimens ; K 26584 , Spitsbergen , three specimens ; K 26583 , Spitsbergen , one specimen .

Bioice 2360: female ~ 25 mm, 64 ss 17 ¾ N, 10 ss 49 ¾ W, 391 m.

Type material of `S. vegae ’: two immature specimens, ~ 10 mm, 66 ss 58 ¾ N, 171 ss 35 ¾ W, 20 m.

Distribution. [200] circumpolar, including the North Atlantic, Ba n Bay and the Siberian Arctic Ocean.

Description (adult specimens only). Rostrum powerful. Antennae short. Antenna 1 shorter than antenna 2; ¯agellum nine-articulate; accessory ¯agellum article 2 present. Antenna 2 peduncle (articles 3±5) longer than ¯agellum; article 3 shorter than broad; article 4 shorter than article 5.

Epistome curved (convex) and smooth; epistomal plate (medial keel) not produced.

Mouthparts not elongate or pointed.

Mandible incisor lateral; toothed; left lacinia mobilis present; powerful; laterally expanded; not conical.

Maxilla 1 palp two-articulate; rectangular; apex not reaching above the apex of outer plate; outer plate distally rectangular; ST in a pseudocrown; numbers of ST in ®rst row allometric; ST 1 ordinary (similar to ST 2±4); ST 1±5 all present; ST 6 absent; gap between ST 5 and ST 7; ST A± C, part of second row; inner plate without a well-developed shoulder; setae pappopectinate.

Maxilla 2 gaping and geniculate; outer plate setae without distal hooks; distal cleft absent; inner plate setae row A covering the entire margin, appressed to row B; row A setae pappopectinate; row B setae proximally simple, distally with cusps; row C present; row D absent.

Maxilliped palp four-articulate; article 2 distally unproduced; dactylus distally simple (pointed); inner plate not exceeding base of palp article 2; ®ve nodular setae; medial setae-row present, not reduced, transverse, setae pectinate; distal setae-row present; inner setae-row present; setae large and powerful; outer plate outer setaerow present, marginal, setae attached in a deep hollow, short and straight; inner setae-row absent; distal setae-group absent.

Labrum elongate; lobes symmetrical, not reduced.

Labium distally narrowing; distally with one pointed ®nger.

Coxal plates and basis on the pereopods smooth. Coxae 1±3 contiguous.

Pereopod 1 coxal plate deeper than basis; propodus subovate. Pereopod 2 longer and thinner than pereopod 1; ischium not elongate, ratio length:breadth not exceeding 1.5; ischium distal posterior margin with plumose setae; propodus subovate; palm absent.

Pereopod 4 coxa posteroventral lobe very large, reaching beyond the base of pereon segment 7; basis anterior and posterior margins with long setae; plumose setae on distal anterior and posterior margins; ischium with plumose setae on posterior distal margin.

Pereopod 6 basis posteriorly expanded; expansion conspicuous, concave, with a row of long plumose setae.

Pereopod 7 basis anterior margin straight, posteriorly expanded with distal margin linear, no medial row of setae.

Oostegites on pereopods 2±5, gills on pereopods 2±7.

Pleonite 1±3 dorsally smooth.

Urosome: articulation between urosome segments 2 and 3 present. Uropod 1 peduncle longer than rami; outer ramus shorter than inner. Uropod 2 peduncle shorter than rami; outer ramus as long as inner. Uropod 3 peduncle shorter than half length of rami; outer ramus uni-articulate; as long as inner.

Telson longer than broad; longer than uropod 3 peduncle; cleft (open), distally rounded; no submarginal setae on apex of each lobe.

Males: unknown.

Remarks. Examination of the types (two immature specimens, see ®gure 2) of S. vegae revealed that it is identical to immature specimens of S. ampulla . The rostrum, number of articles in the ¯agellum of the ®rst antenna, basis of pereopod 6 and epimeral plate 3 are all characters that are subject to allometric growth, and these were the characters that led Oldevig (1959) to erect a new species based on his material from the Siberian Arctic Ocean.

BruÈggen’s (1909) ®gures of the present species ®t very well with both the descriptions and the ®gures presented herein, except for one important character, the ®rst maxilla. According to BruÈggen, the palp is uni-articulate, while in all the material examined by the present authors, the palp is composed of two articles.

In both Barnard and Karaman (1991: 682) and Moore (1992: 932), the setae on the outer plate of maxilla 2 were incorrectly treated as possessing hooks distally; the setae are distally curved, but not hooked (see ®gure 2).

At present, Stegocephalopsis consists of four species, two of which are of highly doubtful generic status (see remarks under the genus). Furthermore, the two remaining species, S. ampulla and S. mamillidacta , do not appear to be closely related, due to some very diOEerent character states in e.g. the mouthparts (see table 2). They are, however, retained within the same genus pending a revision and a cladistic analysis of the entire family (Berge et al., in press).