Austroniscus ovalis Vanhoeffen, 1914

Kaiser, Stefanie & Brandt, Angelika, 2007, Two new species of the genus Austroniscus Vanhoeffen, 1914 (Isopoda: Asellota: Nannoniscidae) from the Antarctic shelf, Zootaxa 1394, pp. 47-68 : 64-66

Austroniscus ovalis Vanhoeffen, 1914

( Figs 10–11 )

Material examined

Paratype: 1 Ψ (1.9 mm), E­Antarctica, Gauss­Station, 70–385 m, Museum für Naturkunde, Berlin, Nr. 17681.

Other material: 3 Ψ (1 preparatory, 2 for SEM), eastern Weddell Sea, 71°18.61`S, 013°56.12`E – 71°18.73`S, 013°56.12`E, PS ANT XXI/2, Station 232–1, 910– 899.6 m, ZMH K–41123.

Diagnosis

Anterior margin of cephalothorax strongly concave. Pereonite 1 not frontally directed, lateral margins rounded; with 2 spine­like appendices inserting ventrally.

Description

Habitus of paratype female ( Figs 10 A, 11A): considerably broadened and flattened. Body about 1.9 mm length, 1.5 times longer than wide. Coxae not visible in dorsal view. Pereonites 2–4 with strongly projected laterofrontal margins, with a small spine apically. Lateral margins of pereonite 1 rounded, with two spine­like appendices inserting ventrally on both sides of cephalothorax and tipped with a small spine, appendices distinctly separated from cephalothorax by a suture line. Pereonites 2–7 of similar size, Pereonite 4 widest, pereonite 1 width 0.6 times pereonite 4 width. Pleotelson ( Fig. 10 B) length 0.3 times body length, twice as long as wide; width 0.9 times pereonite 4 width¸ anterior margin slightly concave, posterior margin strongly rounded. Uropods not projecting above posterior margin ( Fig. 11 B).

Cephalothorax ( Figs 10 A, 11C–D): free, 1.7 times longer than wide, length 0.4 times body length (measured medially), width half of pereonite 4 width, with a well developed rostrum, deeply vaulted. Antennae inserting frontolaterally in a deep fold between rostral crest and anterolateral triangular projections; each fold medially with a single spine. Posterior margin of cephalothorax slightly rounded.

Antennula ( Fig. 10 C) with 6 articles. Article 1 as long as article 2, 1.3 times longer than wide. Article 2 about 4.6 times longer than wide, with 3 long broom setae and 2 small simple setae distally. Articles 3–6 together as long as article 1, each of similar size. Articles 4–5 each with 1 short seta distally, article 6 with 5 setae of varying size terminally.

Antenna ( Fig. 10 C) somewhat longer than body length. Peduncular articles 1–4 short, articles 1–3 of similar size. Article 4 length 0.6 times of article 3 length. Article 2 with a tooth­like projection bearing a spine. Article 3 with a big spine, extending beyond article 4. Article 5 about 1.3 times longer than articles 1–4 together, with 2 robust setae and 8 slender setae laterally and with 2 broom setae and 2 somewhat shorter simple setae distally. Article 6 somewhat longer and more slender than article 5, with 1 robust seta and 8 fine setae laterally, with 2 broom setae and 2 somewhat shorter simple setae distally. Distal 16 flagellar articles tapering in width and length. Flagellar article 1 longest, about one half of peduncular article 5, with 2 fine simple setae laterally; other flagellar articles with single short setae, terminal article with 2 simple setae.

Remarks

The redescription of Austroniscus ovalis was necessary because some characters, e.g. the shape of the first pereonite, were not correctly described by Vanhoeffen (1914) and drawings of the antennae were inaccurate. Yet, these features are very important for the distinction of the three species Austroniscus chelus sp. nov., Austroniscus obscurus sp. nov. and Austroniscus ovalis .

Furthermore, SEM pictures were made from new material of Austroniscus ovalis (BENDEX expedition). These specimens from western Antarctica show some differences from the species sampled by Vanhoeffen (1914) in eastern Antarctica ( Table 2 ): anterior margins of pereonites 6 and 7 strongly convex ( Fig. 11 A); operculum anteriorly extended ventrally compressing sixth and seventh pereonite ( Fig. 11 B). These differences are regarded as a variation within Austroniscus ovalis , and do not present the characters of a new species.

Figures

FIGURE 10. Austroniscus ovalis Vanhoeffen, 1914, paratype female (Museum für Naturkunde, Berlin, No. 17681); A, habitus, dorsal view. B, Plt, ventral view. C, A 1 and A 2. Scale bar = 1 mm.

FIGURE 11. Austroniscus ovalis Vanhoeffen, 1914, paratype female (BENDEX, ZMH K – 41123), SEM; A, habitus, dorsal view. B, Plt, ventral view. C, cephalothorax frontally. D, cephalothorax dorsally.