Plumulojassa, Conlan, 2021

Conlan, Kathleen E., 2021, New genera for species of Jassa Leach (Crustacea: Amphipoda) and their relationship to a revised Ischyrocerini, Zootaxa 4921 (1), pp. 1-72 : 9-10

Genus Plumulojassa n. gen.

Description of male. Maximum body length 4.1 mm.

Head lobe: triangular, apically acute.

Antenna 1: accessory flagellum 1 article.

Antenna 2: slightly stouter than antenna 1 but hardly longer, filter setae somewhat shorter, never with plumose setae; flagellum with at least the last two articles bearing posteriorly curved spines, first article considerably longer than any of the following articles.

Maxilla 1: inner plate bearing a few short, fine setae; palp without setae at the base of article 1, article 2 with 1 row of facial setae.

Gnathopod 1: coxa rectangular; propodus defined by 3 spines (medial-lateral-medial), these mid-distant along the palm; dactyl not facially striated.

Gnathopod 2: with a gill; coxa deeper posteriorly; basis, anterolateral and anteromedial margins clothed in long plumose setae; carpus less than 1/4 propodus length; propodus, palm with a broad, bifid or trifid hinge tooth, defined by two narrow, apically acute teeth, these reaching nearly to the depth of the hinge tooth, thus giving the palm a transverse appearance; dactyl shorter than the propodus, inner margin slightly sinuous, tip reaching beyond the posterior defining tooth; dactyl, cusps reduced to small buttons interspersed with a few short setae.

Pereopod 3: coxa deepest at the centre; basis not slenderer in larger males, margins convex; merus overlapping the carpus, anterior margin bearing a series of single plumose setae; propodus not posteriorly spinose.

Pereopods 5–7: at least one basis posterodistally produced, anterior margin with a few short setae and no spines; merus not posteriorly spinose; carpus bearing 2 spines at the posterodistal angle on pereopod 5 and sometimes also on pereopod 6; spines lacking on pereopod 7; propodus not markedly expanded anteriorly; dactyl without facial striations, posterior (outer) margin not cusped distally, anterior (inner) margin bearing a seta only at the unguis.

Pleopods: rami long, length> depth of the pleon, each with 2 coupling hooks.

Urosome: segment 1 bearing a pair of setae dorsally.

Uropod 3: peduncle mid-ventrally setose, without mid-dorsal spines or mid-ventral setae, but with a crown of spines dorsomedially at the insertion of the rami, and a small cluster of setae distolaterally; outer ramus not setose mid-dorsally, tipped by a basally immersed, dorsally recurved spine, a single seta at the spine’s point of immersion and a dorsal cluster of minute cusps proximal to the spine, none of these cusps particularly larger than the other; inner ramus with a single apical spine.

Telson: dorsolateral cusps accompanied by setae (1 long, single and 2 short, plumose) but without spines.

Description of adult female. Body length at maturity 2.4–4.0 mm. Character states as in the male except as follows.

Brood plates: broad, setae abundant, hook-tipped.

Antenna 2: posterior filter setae long, not shorter in larger individuals.

Gnathopod 1: basis not flanged, without plumose setae.

Gnathopod 2: propodus much larger and different in shape from the propodus of gnathopod 1 but differing only in the following respects from the large male: size slightly smaller, hinge tooth bifid, distal palmar tooth more central, proximal tooth little more than an acute expansion, bearing a large, single medial defining spine; dactyl, inner margin straight, tip apposing the defining spine.

Type species. Podocerus ocius Bate, 1862 (monotypy).

Etymology. The name refers to the abundant plumose setae on the anterior legs, particularly gnathopod 2, which makes this genus unmistakable among the Jassa -like genera, even at young stages.