Cryosignum lunatum ( Hale, 1937 ) Hale, 1937

Just, Jean & Wilson, George D. F., 2007, Revision of Austrosignum Hodgson and Munnogonium George & Strömberg (Paramunnidae) with descriptions of eight new genera and two new species, (Crustacea: Isopoda: Asellota), Zootaxa 1515, pp. 1-29 : 14-16

Cryosignum lunatum ( Hale, 1937) , comb. nov.

Figs 5–6

Paramunna lunata Hale, 1937: 41 , fig. 17.

Pleurosignum lunata ? — Menzies (1962: 55).

Pleurosignum lunata . — Kensley (1977: 259).

Paramunna antarctica ( Richardson, 1908) , identification by Hale (1937: 38, fig. 15), here determined.

Not Austrosignum grande Hodgson, 1910 . — Synonymy proposed by Kussakin (1982: 94).

Not Paramunna lunata . — Brandt (1999: 130, figs 1–2).

Type fixation. Holotype, terminal male, SAMA C3725. — Original designation. Material examined. Holotype. Terminal ɗ, 2.7 mm, Antarctica , Adelie Land, Main Base, Boat Harbour,

67°S 142° 36’E, 3.5–7 m (2–4 fms), September 1913, SAMA C3725.

Paratype. Terminal ɗ lacking pleotelson and all pereopods, same data as holotype, SAMA C3729.

Other material. 3 young ɗ, 2 Ψ, identified as Paramunna antarctica ( Richardson, 1908) by Hale (1937), same data as holotype and paratype, SAMA C6339. 1 fully developed Ψ, Antarctica , Prydz Bay, Davis Station, 68o 34.5'S 77o57'E, M. Tucker, Site A, 24 January 1982, NMV J4766. 2 near terminal ɗ, Antarctica , Prydz Bay, Davis Station, 68o 34.5'S 77o53'E, M. Tucker, Site C, 25 January 1982, NMV J4775. 1 Ψ, Antarctica , Prydz Bay, Davis Station, 68o 38'S 77o48'E, M. Tucker, Site 9, 6 January 1982, NMV J55501 . 1 ovigerous Ψ, Antarctica , Prydz Bay, Davis Station, 68o 34.5'S 77o 53'E, M. Tucker, Site C, 4 June 1982, NMV J4777.

Description. Body width 0.57 length in female, 0.43–0.53 in male (largest value terminal male), widest in female at pereonite 3, in terminal male at pereonite 1. Head longer in male than female, length 0.71 width in terminal male, otherwise length 0.46 width; length posterior to eyestalks 1.4 anterior length, 2.5 anterior length in terminal male; head of terminal male posteriorly fused to pereonite 1. Frontal margin without angular lateral margins adjacent to antennae, shallow convex, almost straight medially. Eyestalks in female length 2.75 width, terminal male length 4.5 width, apex rounded, shaft before apex approximately parallel, long axis angling forward at approximately 30° in female, 40–60° in male (larger value terminal male).

Pereonites 1–4 lateral margins not projecting, coxae visible in dorsal view, except in adult females. Pereonite 1 of terminal male greatly enlarged. Pereonite 1 sagittal length in female 2.3 pereonites midline length, 3.6 in male. Pereonites 1–7 dorsal surface with transverse ridges. Pereonite lateral margin 1–7 rounded.

Pleon length 1.40 width. Pleonite 1 width 1.1 distance between uropods (n=3), length 0.3 width (n=2). Pleotelson laterally rounded, lacking inflection between lateral and proximal margins, without proximal neck; lateral margin convex; posterior margin produced (terminal male apex more rounded than others), forming 90° angle, evenly curving into lateral margin.

Antennula articles 1–2 combined extending beyond eyestalk apex; article 1 shorter than 2, width subequal to 2, tubular; 4–6 of subequal length, shorter than 3.

Antenna article 3 in ventral view inflated midlength, margins curved, width 0.53 length, article 5 distinctly longer than 4; flagellum with 11 articles, proximal article distinctly longer than more distal articles.

Pereopodal coxae I–IV lateral margins rounded in dorsal view (except for coxa I of terminal male); pereopod I coxa of terminal male with anteriorly projecting large angular plate fused to pereonite; basis anterior margin smooth, basis length 2.9–4.4 width (largest value terminal male, n=2); carpus oval, posterior margin with 1 denticle proximal to robust setae, 1 denticle between robust setae (tiny); propodus narrowing distally to insertion of dactylus, with 2 robust setae on opposing margin.

Male pleopods I lateral lobes distinctly projecting from midlateral margin, width 0.3 distance to midline; distal projection length 0.31 pleopod total length, forming acute angle, with pointed apices. Female operculum ovoid, width 0.86 length.

Uropods dorsal and directly adjacent to lateral margin of pleotelson.

Size. Largest Ψ, 2.0 mm; largest ɗ, 2.7 mm.

Distribution. Adélie Land to Princess Elizabeth Land, Antarctica . 3.5–7 m (2–4 fms; depths not known for Davis Station samples).

Remarks. The specimens identified as Austrimunna antarctica by Hale (1937) are in fact females of Cryosignum lunatum . Several factors argue for this observation.

1.The holotype and paratype males (both terminal) of C. lunatum and the smaller A. antarctica were collected at the same locality.

2.All specimens share the transverse ridges on the dorsal surface.

3.Pereopod I of all specimens share the characteristic oval carpus, and a propodus with 2 robust setae on the opposing margin.

4.All specimens have a mandible palp.

5.The smaller specimens are not Austrosignum antarctica (see Just & Wilson, 2004 for redescription and reillustration of that species).

In addition, the specimen described by Brandt (1999, as Paramunna lunata ) from the South Shetland Islands is not this species because it lacks dorsal ridges and the uropodal exopod is extremely short.

Terminal males of Cryosignum lunatum differ from similar stages of C. incisum (features of which are in parentheses) as follows: antennular article 1 distally truncate (distally angular), uropods recessed (uropod not recessed, protopod exposed), pereon with low rounded transverse ridges (no ridges), pleotelson without extension or “neck” after pleonite 1 (with distinct elongation). Other features that differ between the two species may be owing to the syntype male of C. incisum not being fully terminal.

Figures

FIGURE 5. Cryosignum lunatum (Hale, 1937), comb. nov. A, holotype, terminal male. B, young male. C, ovigerous female. (B and C identified as Paramunna antarctica (Richardson) by Hale 1937). a, antenna; au, antennula; cv, head ventral view; mdp, mandible palp; up, uropod. Scale bar for all habitus figures: 0.5 mm.

FIGURE 6. Cryosignum lunatum (Hale, 1937), comb. nov. A, holotype, terminal male. B, young male. C, ovigerous female. D, paratype, male. (B and C identified as Paramunna antarctica (Richardson) by Hale 1937). md, mandible; op, female operculum; p 1, pereopod I (all shown to same scale); pl 1, pleopod I.