Stegosoladidus antarcticus, Berge, 2001

Berge, JØrgen, 2001, Revision of Stegosoladidus Barnard and Karaman, 1987 (Crustacea: Amphipoda: Stegocephalidae), redescription of two species and description of three new species, Journal of Natural History 35 (4), pp. 539-571 : 551-558

Stegosoladidus antarcticus n. sp.

(®gures 12±17)

H OLOTYPE. Berlin ZMB 27335, female, 75ss25.40¾S, 16ss26.63¾W, 198±260 m.

PARATYPES. Three immature females, Berlin ZMB 27335 .

Additional material. WED 96 (Brussels), st.11, eight specimens, 73ss22¾S, 21ss10¾W, 333± 338 m.

Distribution. Weddell Sea.

Description. Rostrum very small.

Antennae short. Antenna 1 as long as antenna 2, ¯agellum four-articulate, accessory ¯agellum with two articles. Antenna 2 peduncle (articles 3±5) longer than ¯agellum, article 3 elongate, articles 3 and 4 geniculate; article 4 longer than article 5.

Epistome produced laterally, rectangular, with a long ridge on each side; epistomal plate (medial keel) produced into a small elongate medial ridge covering the entire epistome.

Mandible incisor transverse, smooth, left lacinia mobilis present, reduced, laterally straight, not conical.

Maxilla 1 palp uni-articulate, rectangular, apex not reaching above the apex of outer plate; outer plate distally rounded, ST in a pseudocrown, ST ®rst row with six setae (ST1±5, ST7), ST 1 ordinary (similar to ST 2±4), gap between ST 5 and ST 7, ST A present, located distally, part of ®rst row, ST B absent, ST C present; inner plate without a well developed shoulder, setae pappose.

Maxilla 2 ordinary, outer plate setae without distal hooks or cleft; inner plate setae row A covering the entire margin, appressed to row B, row A setae pappose, three or four ®rst setae diOEerentiated from the other setae (weakly pappopectinate); row B setae proximally simple, distally without cusps; row C present; row D absent.

Maxilliped palp four-articulate, article 2 distally unproduced, articles 1±3 inner margins without plumose setae; inner plate without nodular setae; medial setae row present, not reduced, transverse, setae simple; distal setae row present, setae simple; inner setae row present, reduced to one or two setae, setae not conspicuously large; outer plate outer setae row present, marginal, setae attached normally, long robust, straight; inner setae row present but strongly reduced, setae long robust, setae slender, parallel to, but not appressed to outer row; distal setae-group present, setae attached normally, long robust.

Labrum very short; lobes symmetrical, both lobes reduced.

Labium distally broad, oval.

Coxal plates and basis on the pereopods covered with very short setae: coxae 1±3 overlapping, broad.

Pereopod 1 coxal plate deeper than basis, propodus subovate.

Pereopod 2 longer and thinner than pereopod 1, ischium elongate, ratio length 5 breadth exceeding 1.5, distal posterior margin with plumose setae, propodus subrectangular, palm developed.

Pereopod 4 coxa posteroventral lobe large, reaching about the base of pereon segment 7; basis anterior and posterior margins without long setae, no plumose setae on distal anterior and posterior margins, ischium with plumose setae on posterior distal margin.

Pereopod 6 basis posteriorly expanded, expansion conspicuous, rounded posteriorly, with no long plumose setae.

Pereopod 7 basis anterior margin straight, distally rounded, with medial row of short and robust setae, carpus present, dactylus present.

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

Pleonite 1±3 dorsally smooth.

Urosomites 2 and 3 free. Uropod 1 peduncle longer than rami, outer ramus as long as inner. Uropod 2 peduncle longer than rami, outer ramus as long as inner. Uropod 3 peduncle at least as long as rami, outer ramus two-articulate, outer ramus as long as inner.

Telson as long as broad, shorter than uropod 3 peduncle, cleft, apically rounded, with submarginal setae on apex of each lobe.

Males: unknown

Etymology. Referring to its truly Antarctic distribution.

Remarks. The present species appears to be very closely related to S. ingens , especially when considering the striking similarities in mouthparts. However, the external morphology is almost identical to that of S. debroyeri (habitus not ®gured for the present species), mainly due to their large coxae 1±4 covering the pereopods. As S. antarcticus and S. debroyeri appear to be sympatric, it is very di cult to distinguish them based on habitus alone. Both S. antarcticus and S. debroyeri have a well developed and almost transverse palm on pereopod 2. However, S. antarcticus and S. ingens both lack nodular setae on the maxilliped. Furthermore, these species both have a narrow and slender palp, and a relatively long outer plate on the maxilliped (see also Remarks under S. debroyeri ).

Stegosoladidus antarcticus has a broad and rounded basis on pereopod 6 (in contrast to the narrow and weakly concave basis of S. debroyeri and S. ingens ) and a well developed palp on the ®rst maxilla (in contrast to S. ingens ).