Austronanus dubius ( Hale, 1937 ) Hale, 1937

Just, Jean & Wilson, George D. F., 2006, Revision of Southern Hemisphere Austronanus Hodgson, 1910, with two new genera and five new species of Paramunnidae (Crustacea: Isopoda: Asellota), Zootaxa 1111, pp. 21-58 : 39-41

Austronanus dubius ( Hale, 1937) , comb. nov.

( Fig. 9 )

Paramunna dubia Hale, 1937: 40 , fig. 16. Austrosignum dubia .— Menzies, 1962: 44.

Remarks on type material. The anterior part of the body is somewhat flattened artificially, making it broader than the posterior pereonites.

Material examined

Holotype. Ψ, 1.80 mm, Main Base, Commonwealth Bay, Adelie Land, Antarctica , 67°S 142°36'E, 25–30 fms [46–55 m], 3 September 1912, Hunter, SAMA C4346.

Description. Body width 0.47 length in female, widest at pereonite 2 or 3. Head length 0.63 width; length posterior to eyestalks 0.75 anterior length. Frontal margin lobe length 0.78 head length; apex bluntly angular in dorsal view, frontal margin adjacent to apex convex, not sinuous. Eyestalks lateral apex rounded, globular, shaft before apex slightly constricted with neck, long axis angling forward at approximately 40°, about as long as wide in dorsal view.

Pereonite lateral margin 1–4 linear, 5–7 rounded. Pereonite 5 in dorsal view distinctly narrower than pereonites 4 and 6. Pereonite lateral margins 6–7 finely denticulate.

Pleon length 0.95 width; pleotelson proximal margin length shorter than lateral margin length. Pleonite 1 width 1.0 distance between uropods, length 0.14 width. Pleotelson proximal margins set at 45º angle with medial axis of pleon, merging into lateral margin without noticeable angle, lateral margins denticulate, with 14–16 denticles per side; posterior margin forming 125° angle, with 3 uniformly fine denticles laterally each side.

Antennula articles 1 and 2 combined reaching eyestalk apex; article 1 longer and broader than 2, inflated, 5–6 of subequal length, longer than articles 3–4.

Antenna article 2 lateral margin with two spines (proximal spine tiny); article 3 in ventral view distally expanded, distolateral margin angular, width 0.64 length, with crenate flange on lateral margin, flange coarse with rectangular subunits, with 1 distal spine; article 5 only slightly longer than article 4; flagellum with 5 articles, proximal article 1.5 length of second article.

Pereopod I basis anterior margin smooth, length 2.5 width; merus with 1 spine on posterior margin (low and rounded); carpus distal width 1.0 posterior margin length; posterior margin with one denticle proximal to robust setae, 2 denticles between robust setae (smaller tooth proximally), one denticle distal to robust setae; propodus narrowing distally to insertion of dactylus, with 2 robust setae, with crenate ridge. Pereopods V–VII coxae lateral margin denticulate, coxa V with small denticles, coxae VI–VII with denticles grading to spines posteriorly.

Female operculum distal part tapering with concave distolateral margins, width 0.88 length.

Uropods dorsal and directly adjacent to lateral margin of pleotelson.

Size. Largest female 1.80 mm.

Distribution. Known only from the type locality.

Remarks. Austronanus dubius is the largest species in the genus. Article 3 of the antennae is similar to that in A. glacialis , but A. dubius differs from that species in the evenly convex lateral margins of the head, lack of anterodistal spines on merus of pereopod I, weak dentition on lateral margins of pereonites 5–7 and coxae 5 and 6, and a more ovoid female operculum. Austronanus dubius differs from the other two species in the genus with evenly convex lateral margins of the head, A. dentatus and A. gelidus , as follows: A. dentatus has only 5 articles in the antennulae and laterally elongate coxae V– VII; in A. gelidus , article 3 of the antennae is much narrower, lateral margins of pereonites 5 and 6 and coxae 5 and 6 are smooth, and pleotelson more angular between proximal and lateral margins.

Figures

FIGURE 9. Austronanus dubius. Holotype, female. a, antenna; au, antennula; cl, lateral view of head; cv, ventral view of head; dv, dorsal view; mdp, mandible palp; op, operculum; p 1, pereopod I; pe 5 ­ 7, pereonites 5 ­ 7 with coxae; pt, pleotelson; up, uropod. Habitus scale bar: 0.5 mm.