Cryosignum nordenstami, Just & Wilson, 2021

Just, Jean & Wilson, George D. F., 2021, Redescriptions and new species in the ‘ Austrosignum-Munnogonium’ complex sensu Just & Wilson (2007), mainly from the Southern Hemisphere (Crustacea Isopoda: Paramunnidae), Zootaxa 4952 (3), pp. 401-447 : 415-416

Cryosignum nordenstami sp. nov.

( Fig. 8 )

Austrosignum glaciale Hodgson, 1910 .— Nordenstam, 1933: 241, fig. 66.

‘ Cryosignum’ undescribed species.— Just & Wilson, 2007: 14.

Type fixation. Holotype, ♀, SMNH 79450 .—Here designated.

Type locality. South Georgia, north of Grytviken.

Etymology. The species is named for Dr Åke Nordenstam, who reported these specimens from South Georgia.

Material examined. Holotype. ♀ (pereiopods I missing), 1.5 mm. South Georgia, north of Grytviken , 54°22’S, 36°28’W, 12–15 m, sand and algae, Swedish Antarctic Expedition 1901–1903, stn 28, 24 May 1902, SMNH 79540 .

Paratype. Same data as holotype. SMNH 79541 , (♂ 1.5 mm, pereiopods I and pleopod I missing) .

Description. Body width 0.43 length in female, 0.40 in male, widest at pereionite 3 in both. Head length 0.40 width (♀), length posterior to eyestalks 1.4 anterior length. Frontal margin nearly straight with rounded angular lateral margins adjacent to antennae. Eyestalks length 2.4 width, apex rounded, long axis angling forward at 35–40°.

Pereionite 1 female sagittal length 1.4 pereionites midline length, 1.8 in male; pereionite 1–7 lateral margin rounded. Coxal plates 1–7 simple, squarish (except 1 in male bluntly pointed), visible in dorsal view.

Pleon length 1.9 width in female, 1.7 in male. Pleonite 1 width subequal to distance between uropods in both sexes, length 0.5 width in female, 0.6 in male. Pleotelson slender, laterally convex, smooth, with small inflection between lateral and proximal margins; posterior margin forming 60° angle, with slight concavity level with uropods in female, 80° angle without concavity in male, apex in both pointed.

Antennula with 6 articles, articles 1–2 combined extending beyond eyestalk apex; article 1 about half length of 2, inflated; articles 3, 5 and 6 of subequal length, longer article 4.

Antenna article 3 tubular, width 0.33 length, article 5 distinctly longer than article 4; flagellum proximal article distinctly longer than more distal articles.

Operculum ovoid, width 0.7 length, without lateral concavity, apex pointed.

Uropods dorsal and directly adjacent to lateral margin of pleotelson, protopod hidden or absent.

Size. Largest female 1.5 mm; largest male 1.5 mm.

Distribution. South Georgia, 12– 15 m.

Remarks. Nordenstam (1933) reported two females and one male of Austrosignum glaciale Hodgson, 1910 from Station 28. He further noted that the largest female measured 1.7 mm. We have seen only one female and one male. Since our female measures 1.5 mm and has not been dissected (mandible, operculum; see Nordenstam’s fig. 66), we must have had the smaller female for examination. Hence, Nordenstam’s fig. 66b (‘Right second pereiopod, immature female’) seems to belong to the specimen here designated as holotype of Cryosignum nordenstami sp. nov. The second, larger female, if still in existence, should not be considered a paratype at the moment, because we cannot vouch for its placement in this species.

The paratype male is likely to be immature as well, as it is the same size as the female. This would explain why the male does not have the secondary sexual characteristics of more mature and terminal males in other species. Cryosignum nordenstami sp. nov. differs from congeners by the narrower, pointed pleotelson.

Figures

FIGURE 8. Cryosignum nordenstami sp. nov., H, holotype, ♀; M, paratype, ♂. md, mandible; op, operculum; up, uropod. Scale for habitus (both), 0.5 mm.