Cryosignum latifrons ( Menzies, 1962 ) 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 : 413

Cryosignum latifrons ( Menzies, 1962) , comb. nov.

( Fig. 7 )

Austrosignum latifrons Menzies, 1962: 50 , fig. 9.

Paramunnidae incertae sedis.— Just & Wilson, 2007: 14, table 1, fig. 1.

Type fixation. Lectotype, ♀, SMNH 3220 .—Here designated.

Type locality. Seno [Gulf of] Reloncavi, southern Chile.

Remarks on type material. Menzies (1962: 50) listed 3 females, but did not designate a holotype. Among these syntypes we have designated the ‘female cotype’ illustrated by Menzies (1962, fig. 9A) as lectotype.

Material examined. Lectotype, ♀, 1.3 mm, Chile, Seno Reloncavi, N of Isla Quellin , 41°51’S, 72°55’W, 100 m, small stones, probably also hard sand, Lund Universitet Chile Expedition 1948–49, 23 January 1949, stn M40, SMNH Type-3220.

Paralectotypes. 2 smaller females (one without head), same data as lectotype, in separate vial together with lectotype, SMNH Type-3220 .

Description (lectotype). Body width 0.6 length, widest at pereionite 3. Head length 0.41 width; length posterior to eyestalks 0.8 anterior length. Frontal margin broadly rounded, without angular lateral margins adjacent to antennae. Eyestalks in female length 1.7 width, apex rounded, shaft constricted in proximal third, long axis angling forward at most 10°.

Pereionite 1 sagittal length 1.7 pereionite midline length; pereionite 1 lateral margin linear to slightly concave, 2–4 rounded, with small posteriorly projecting lobes, 5–7 rounded; lateral margins of pereonites 2–4 with tiny denticles on posterior half.

Pleon length 1.3 width. Pleonite 1 width equals distance between uropods, length 1.3 width. Pleotelson laterally rounded, smooth, lacking inflection between lateral and proximal margins; posterior margin forming 80° angle, evenly curving into lateral margin, margins micro-serrate with simple setae, apex rounded.

Antennula with 6 articles (left aberrant with 5); articles 1–2 combined extending beyond eyestalk apex; article 1 length subequal to 2, inflated, broader than 2; articles 5–6 of subequal length, longer than equal articles 3–4. Antenna article 3 tubular, width 0.50 length, article 5 distinctly longer than article 4; flagellum with 10 articles, proximal article distinctly longer than more distal articles, 2.7 length of second article.

Pereiopod I basis anterior margin smooth, length 1.5 width; carpus oval, distal width 1.0 posterior margin length, posterior margin with 1 tiny denticle proximal to each robust seta; propodus narrowing distally to insertion of dactylus, with 2 robust setae.

Operculum broadly ovoid, width 0.90 length, without concave distal margins, apex rounded.

Uropods dorsal, adjacent to lateral margin of pleotelson; protopod recessed or absent.

Size. Largest female 1.3 mm.

Distribution. Southern Chile, 100 m.

Remarks. In our analysis of the Austrosignum – Munnogonium complex ( Just & Wilson, 2007: 14, table 1, fig. 1) we placed Austrosignum latifrons Menzies, 1962 as Paramunnidae incertae sedis because the species did not unambiguously align with the Cryosignum clade as expected due to lack of males in the type material, although it appeared in our cladogram as sister group to Cryosignum . This issue still is not resolved, but we now find the incertae sedis label unhelpful in referring to the species. If we disregard aspects of the diagnosis of Cryosignum ( Just & Wilson, 2007: 14) which refer to males only, this species fits the diagnosis of Cryosignum as opposed to Austrosignum and Munnogonium . We therefore transfer the species from incertae sedis to Cryosignum .

Cryosignum latifrons shares with females of the type species C. lunatum general body shape, eye stalk configuration, a mandible palp, the oval carpus of pereiopod I with 2 straight robust setae, propodus of pereiopod I with 2 robust setae on posterior margin, a perfectly ovoid operculum, and a straight, apically rounded uropod endopod. It differs from all species of Cryosignum in the shape of the lateral margins of pereionites 2–4, each of which has a pronounced posterior, rounded, finely serrate lobe, and in the broadly rounded frontal margins reaching to the base of the eyestalks.

Figures

FIGURE 7. Cryosignum latifrons (Menzies, 1962). Lectotype, ♀. a, antenna; au, antennula; cvv, head ventral view; md, man- dible; op, operculum; p1, pereiopod I; up, uropod; 1–4, pereionites 1 to 4 lateral margins. Scale for habitus, 0.5 mm.