Austrosignum Hodgson

Austrosignum Hodgson

Austrosignum Hodgson, 1910: 65.

Type species. Austrosignum glaciale Hodgson, 1910. —Subsequent designation.

Species included. A. escandellae Castelló, 2004, A. glaciale Hodgson, 1910.

Diagnosis. Head front margin evenly convex. Pereonites dorsally smooth or with low transverse ridges. Pleotelson lateral margins smooth. Eyestalk length at least twice greatest width. Antennula article 1 at most as long as eyestalk. Mandible palp absent. Pereopod I carpus triangular, with 2 straight robust setae on posterior margin and one smaller, straight robust setae more distally, with rectangular, ciliated spine on margin between main robust setae; propodus with simple setae only. Pereopod II carpus and propodus posterior margin with a few short robust setae. Uropod endopod acutely pointed, curving medially.

Note on type species. Hodgson (1910) did not fix a type species for his new genus Austrosignum. He described the two new species A. grande and A. glaciale in that sequence. Menzies (1962: 50) was the first author to fix a type species for Austrosignum Hodgson by designating A. glaciale as the type species of the genus. Although he thereby violated ICZN Recommendation 69B (11, “position precedence”), Menzies’ designation is valid according to ICZN Article 69 (a) (iv). Subsequent statements by several authors that A. grande is the type species of Austrosignum are therefore incorrect. We agree with Kussakin (1982) that Austrosignum glaciale and A. grande are synonymous, but under the former name rather than the latter as proposed by Kussakin.

Remarks. Austrosignum differs from Munnogonium as follows (characters of the latter in brackets): antennula article 1 not reaching apex of elongate eyestalks (much longer than vestigial eyestalks), pereopod I carpus posterior margin with 2 robust setae plus 1 small robust seta more distally (with 3 equal sized robust setae); pereopod II carpus and propodus posterior margin with short, stout robust setae (elongate, thin robust setae), uropod endopod acutely pointed, curving medially (straight, rounded truncate), female operculum ovoid (distal part tapering with concave distolateral margins). Austrosignum is more similar to Cryosignum gen. nov. (below), but differs as follows: mandible palp absent (present in Cryosignum), pereopod I carpus triangular with 2 long and 1 short robust setae posteriorly (oval with 2 robust setae), uropod endopod acutely pointed, curving medially (straight, rounded truncate), terminal male enlarged pereonite 1 with broadly rounded anterior margin, not fused to coxa (strongly and acutely forward projecting, coxa fused to pereonite), terminal male head freely articulating with pereonite 1 (fused to pereonite 1).

The third smaller carpal seta is removed from the posterior margin and inserted on the medial face. In A. glaciale, this seta is easily seen in lateral view, but we have examined undescribed species of Austrosignum, in some of which the seta is inserted medially just behind the most distal of the normal 2 robust setae. In that position, the third seta can be difficult to observe in lateral view. The third robust seta has not been reported from A. escandellae. If not found after reviewing the species, we are uncertain if A. escandellae should be retained in Austrosignum.