Mimonecteola antarctica, Zeidler, Wolfgang, 2012

Zeidler, Wolfgang, 2012, A new species of Mimonecteola (Crustacea: Amphipoda: Hyperiidea: Mimonecteolidae) from the Southern Ocean, Zootaxa 3308, pp. 63-67 : 63-67

Mimonecteola antarctica sp. nov.

( Figs 1 & 2 )

Material examined. Holotype. Female 8.0 mm ( USNM 1090275); Southern Ocean, Pacific Sector, Amundsen Sea [62°11’– 62°20’S 115°02’– 114°24’W], R/V Eltanin, stn. 901, cruise 11, University of Southern California, 3477– 3678 m, 7 January 1964.

Allotype. Male (?) 7.2 mm ( USNM 1090274); Southern Ocean, Atlantic Sector, north-west of Elephant Island [60°12’– 60°21’S 59°00’– 59°14’W], R/V Eltanin, stn. 449, cruise 6, University of Southern California, 1610 m, 15 January 1963.

Description of holotype (figs 1 & 2). Female, 8.0 mm; immature judging by the under-developed oostegites. Pereon moderately inflated due to enlargement of pereonites 1–4. Head with short, hook-shaped rostrum. Eyes small or barely discernable. Antennae 1 as long as head and first 1.5 pereonites combined (measured medially). Antennae 2 similar in length to antennae 1, with relatively long, slender terminal article. Gnathopod 1; basis marginally shorter than remaining articles combined; carpus and propodus similar in length; propodus oval-shaped with numerous fine setae distally; dactyl relatively straight, length about half propodus. Gnathopod 2; length 1.4 x gnathopod 1; articles relatively more slender but of similar proportions to those of gnathopod 1; propodus with few long setae on margins and distally. Pereopod 3 marginally longer than pereopod 4; basis length almost 2.5 x merus; carpus slightly expanded with several moderate setae on distal margin, length about twice merus; propodus relatively narrow, length 1.4 x carpus; dactyl relatively straight, length slightly more than 0.2 x propodus. Pereopod 4 marginally shorter than pereopod 3 but of similar structure; basis length about twice merus, as long as carpus; propodus length about 1.3 x carpus. Pereopod 5 is relatively feeble compared to other pereopoda, with more slen- der articles except for the propodus; length marginally more than 0.7 x pereopod 4; basis length about twice merus; carpus length about 1.3 x merus; propodus length almost 0.9 x carpus, with tuft of three, slightly stronger, setae on anterodistal corner; dactyl relatively straight with bulbous base, length slightly more than 0.2 x propodus. Pereopod 6; length 1.1 x pereopod 5; basis length about 2.3 x merus; carpus length 1.7 x merus; propodus relatively narrow, slightly longer than carpus; dactyl relatively straight, length slightly more than 0.2 x propodus. Pereopod 7; length marginally more than 0.7 x pereopod 6; basis length 2.7 x merus; carpus length 1.6 x merus; propodus relatively narrow, length twice merus or 1.2 x carpus; dactyl relatively straight, length almost 0.3 x propodus. Uropoda with relatively slender peduncles and rami; all rami with slightly serrated margins. Uropod 1; peduncle marginally exceeds limit of peduncle of uropod 2, with strong seta on inner distal corner and about mid-way on inner margin; rami of similar length, about two-thirds peduncle. Uropod 2; peduncle with strong seta on inner distal corner; rami of similar length, about 0.8 x peduncle. Uropod 3; peduncle with seta as in uropod 2; inner ramus marginally longer than outer, length 0.9 x peduncle. Telson pointed; width at base almost 0.8 x length, slightly shorter than half of peduncle of uropod 3.

Colour of living specimen not known.

Description of allotype (fig 2). Male (?), 7.2 mm. It is most likely an immature male as there are no oostegite buds and there are, almost indistinguishable, genital papillae at the base of pereopod 7. A damaged specimen with pereopod 4 & 5 (or part) missing from the left and the urosome is incomplete. It is almost identical to the holotype female in relative lengths and structure of the gnathopoda and pereopoda but these appendages seem to be relatively larger than for the holotype, although the specimen is slightly smaller (see fig. 2, all drawn to same scale). The propodus of pereopod 3 is illustrated as relatively shorter but it is bent in the specimen and difficult to illustrate and is actually much longer, similar to the holotype.

Colour of living specimen not known.

Remarks. This species belongs to a group of Mimonecteola species where the propodus of pereopod 5 does not narrow gradually distally towards the dactyl and the anterior margin is armed with relatively strong setae ( M. subchelata Vinogradov, 1964 ) or ends with a tuft of 3–4 stronger setae on the anterodistal corner ( M. carlsbergi Zeidler, 2009 and females of M. mixta Vinogradov, 1964 ). These species also have relatively shorter dactyls (except for pereopod 5 & 6 of M. subchelata ) than M. macronyx Barnard, 1932 or M. beebei Shoemaker, 1945 .

Mimonecteola antarctica is readily distinguished from M. mixta and M. subchelata by the dactyl of pereopod 7 which is normal and not partly retractile. Also, pereopod 5 is relatively shorter and is not weakly subchelate, although the anterodistal corner bears a few, slightly stronger, setae thus resembling M. mixta (females) and M. carlsbergi . In addition M. subchelata is distinguished by the relatively long dactyls of pereopod 5, forming a distinctive subchelate process and by the relatively longer telson (about 0.8 x length peduncle of uropod 3) and in M. mixta the merus of pereopods 6 & 7 is relatively longer, and in males the dactyl of pereopod 5 is relatively longer, forming an almost subchelate process. Thus, this new species is most similar to M. carlsbergi but is readily distinguished by the relatively shorter and more feeble pereopod 5 and the relatively longer second antennae. In addition the following differences have been noted; M. antarctica versus M. carlsbergi (in brackets). The dactyls of pereopods 3–7 are relatively longer, slightly more than 0.2 x propodus (slightly less than 0.2 x propodus); the propodus of pereopods 3 & 4 is relatively longer, about 1.3–1.4 x carpus (only slightly longer); pereopod 5 is relatively shorter and more feeble, length about 0.75 x pereopod 4 (subequal in length); the propodus of pereopod 5 is slightly shorter than the carpus (slightly longer); pereopod 6 is relatively shorter, with pereopod 3 the longest pereopod (pereopod 6 is the longest); the merus of pereopod 6 & 7 is relatively shorter and the articles of pereopods 5–7 are relatively bare whereas in M. carlsbergi the merus and carpus are armed with relatively long, fine setae on the anterior margin.

The only other species of Mimonecteola recorded from the Southern Ocean, M. beebi , (see Zeidler & De Broyer 2009) is distinguished from M. antarctica by the structure and length of pereopod 5 and by the relatively longer telson (about 0.8 x peduncle of uropod 3).

A new key to the species of Mimonecteola follows to include the new species described here.

Figures

FIGURE 1. Mimonecteola antarctica sp. nov., holotype female, 8.0 mm, Amundsen Sea (Eltanin stn. 901), USNM 1090275. A, lateral view. Scale bars = 1.0 mm (A); 0.5 mm (Us); 0.2 mm (A 1, A 2).

FIGURE 2. Mimonecteola antarctica sp. nov.; top—holotype female 8.0 mm, Amundsen Sea, USNM 1090275; bottom—allotype male, 7.2 mm, north-west of Elephant Island (Eltanin stn. 449), USNM 1090274. Scale bar = 0.5 mm.