Austrosignum pilosum, 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 : 403-405

Austrosignum pilosum sp. nov.

( Fig. 1 )

Type fixation. Holotype, T ♂, AM P60883. —Here designated.

Etymology. The epithet is from the Latin pilosus (= hairy), which alludes to many long setae on the dorsal surface.

Type Locality. Macquarie Island, Australia.

Material examined. Holotype. T ♂, 1.8 mm. Aerial Cove , Macquarie Island, Australia, 54°29’S, 158°57’E, coll. R. Ricker, 12 Dec 1977, from algae in Durvillea zone, MA–111, AM P60883.

Paratype. Nearly T ♂, 1.3 mm, Caroline Cove, Macquarie Island, Australia, inner cove north of hut, 54°46’S, 158°48’E, 13 m, Codium flat adjacent to Macrocystis bed, 17 January 1978, J.K. Lowry ( SCUBA), stn MA-311, NMV J52113 .

Description (terminal male). Body tapering posteriorly, width 0.52 length, widest at pereionite 2 and 3. Head length 0.44 width; length posterior to eyestalks 1.4 anterior length. Frontal margin broadly rounded. Eyestalks length 4 times width, apex rounded, long axis angling forward at 35–40°.

Pereionites lateral margin 1–7 rounded. Pereionites 1–3 coxae barely visible in dorsal view except on pereionite 2; coxae visible on pereionites 4–7, rounded, each with single simple seta. Pereionite 1 sagittal length in male 1.9 pereionite midline length.

Pleon length 1.4 width. Pleonite 1 width 0.8 distance between uropods, length 0.3 width. Pleotelson lacking inflection (‘neck’) between lateral and proximal margins; lateral margin s convex, smooth; posterior margin apex narrowly rounded; posterior margin forming 80° angle, set apart from lateral margins by concavity distal to uropods.

Antennula articles 1–2 combined extending beyond eyestalk apex; article 1 tubular, length and width subequal to 2; articles 4–6 of subequal length, all shorter than 3, (left side of holotype aberrant with 2 short terminal articles only). Antenna article 3 tubular, width 0.43 length, article 5 distinctly longer than article 4; flagellum with 7 articles, proximal article subequal to article 2, distal articles shorter.

Pereiopod I basis anterior margin smooth, length 2.1 width; merus posterior margin with one robust seta on distal margin; carpus triangular, distal width 1.1 posterior margin length, posterior margin with 2 large robust setae and 1 distal short robust seta, with crenate projection proximal to each large robust setae; propodus narrowing distally to insertion of dactylus, with crenate ridge on opposing margin.

Pleopod I lateral lobes distinctly projecting from lateral margin, width 0.35 distance to midline, distal sublobe with tuft of simple setae; distal projection length 0.30 pleopod total length, forming acute angle of 70°, with pointed apices.

Uropods inserted on lateral margin of pleotelson; protopod absent.

Size. Largest male 1.8 mm.

Distribution. Macquarie Island, Australia, 13 m.

Remarks. Terminal males of Austrosignum pilosum sp. nov. differ from those of the type species A. glaciale Hodgson, 1910 ( Just & Wilson, 2007, figs 2–3) as follows: the body is wider relative to length with long setae dorsally; the pleotelson lacks a neck, and pleopod I is in a position close to pleonite 1 (ventral view); and the lateral margins distal to the uropods are distinctly concave. Austrosignum latum sp. nov. (below) is even broader (both sexes) than the above mentioned species, and has a short pleotelson neck with pleopod I set back from pleonite 1; dorsally it has short setae only. Austrosignum escandellae Castelló, 2004 differs from all three species by an irregularly sculpted dorsal surface, and by apparently lacking the small distal third robust seta on the carpus (see Just & Wilson, 2007: 9).

Figures

FIGURE 1. Austrosignum pilosum sp. nov. Holotype, T♂. a, antenna; au, antennula; cvv, head ventral view; p1–2, pereiopod I and II; pl1, pleopod I; up, uropod. Scale for habitus, 0.5 mm.