Pleojassa orientalis, 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 : 48-49

Pleojassa orientalis n. sp.

( Fig. 28 )

Description of adult female. Holotype: Length 9.8 mm.

Antenna 2: overlapped by antenna 1 to the end of article 5; article 5, posterior margin bearing long simple setae only, without plumose setae; flagellum 3 articles, article 1 89% of the full flagellum length.

Mandible: palp articles 2 and 3 without a dorsal fringe of setae; raker spines, number not measured.

Gnathopod 1: coxal margins, anterior 140% of dorsal length; ventral margin shallowly convex; basis, anterior margin with a few short setae distally, posterior margin not setose; carpus, length 75% of propodus length, posterior lobe 59% of anterior margin length, without an anterodistal setal cluster; propodus, palm convex, with two defining spines slightly proximal of centre.

Gnathopod 2: coxal margins, anterior 44% and posterior 73% of ventral length; ventral margin shallowly concave; carpus less than 1/4 the length of propodus; propodus, hinge tooth large and conical, not anteriorly bifid, palmar setae plumose, distributed throughout the palm, but not so dense as to obscure the palm’s shape, palmar angle acute, with a single, minute spine at its corner; dactyl, inner margin slightly sinuous.

Pereopod 3: coxa, greatest depth posterior of centre; basis, anterior margin shallowly convex; merus, anterior marginal setae in well separated clusters, central setae, length 1/2 or less the article width, article width 72% of length; carpus 42% overlapped by merus; propodus, width 48% of length.

Pereopods 5–7: setae and spines moderately abundant, basis posterodistally produced, anterior margin spinose; merus, posterior margin not spinose.

Uropod 1: peduncle, posteroventral spinous process underlying 52% of the inner ramus, inner and outer rami with 10 and 6 mid-dorsal spines respectively.

Uropod 2: peduncle, posteroventral spinous process underlying 42% of the inner ramus.

Uropod 3: inner ramus with 2 spines mid-dorsally.

Condition. Without left pereopod 5 and right pereopod 6. Flagellum of right antenna 1 lacking terminal article(s). Right appendages, left pereopod 6, and telson slide mounted.

Description of male. Allotype: Length approximately 6.5 mm; head to end of segment 6, 3.9 mm. Character states as in the female except as follows.

Antenna 2: article 5, filter setae half or less the length of those in the female, interspersed with plumose setae.

Gnathopod 2: as in the female, but palm less densely setose and dactyl inner margin straight.

Condition. Without body segments posterior of segment 6, antennae 1 flagella, left antenna 2 distal flagellum, right antenna 2, left pereopods 5–7, and right pereopods 5 and 7.

Variation. Maximum body length: male unknown, female 9.8 mm. The male is 2/3 the body length of the adult female holotype (judging by relative difference in head length). This suggests that this male may not yet be mature, so it cannot be assumed that larger males lack a thumb as illustrated for the smaller male. Due to lack of material, sexual variation and growth is not well known and only can be inferred from congeners. Judging by its close resemblance to P. multidentata , in which the male is known to grow a thumb, this development is probably similar in P. orientalis . The small male bears plumose setae on the antenna 2 while the adult female lacks plumose setae. However, as in P. wandeli , larger females may have plumose setae.

Type material examined. Holotype, ♀, ovigerous ( AM), type no. P.34955, station no. MA-147, Macquarie Island: Gorilla Head Rock , southeast corner (54 o 29ʹS, 158 o 58ʹE), 23 December 1977, in a small Durvillea antarctica holdfast, 8 m. Allotype, small (juvenile?) ♂ ( AM), type no. P.37924, same location . Paratype, juvenile ♀ ( AM), type no. P.37925, same location .

Etymology. In reference to the eastern location of the species relative to P. multidentata .

Remarks. Pleojassa orientalis differs from P. multidentata in the shape of the gnathopod 2 palm (both sexes) ( Figs 27 and 28 ), and in lacking a cluster of short setae at the anterodistal margin of the carpus of gnathopod 1, which is present in P. multidentata . Pleojassa orientalis may prove to be a geographic variant of P. multidentata , given the wide longitudinal range that Southern Hemisphere species can have ( Figs 1 and 2 ). They are given separate species status herein because these morphological differences are key characters for distinguishing species in Jassa (Conlan et al., in press) and this may be the same case in Pleojassa and other relatives of Jassa .

Figures

FIGURE 1. Distribution records of Plumulojassa ocia, Ventojassa frequens and Hemijassa goniamera. Red dot: identification confirmed by specimen examination; green triangle: literature record (Supplementary Table S1) with identification not confirmed but judged likely to be this species.

FIGURE 2. Distribution records of Pleojassa moorei, P. lowryi, P. wandeli, P. multidentata, and P. orientalis. Red dot: identification confirmed by specimen examination; green triangle: literature record (Supplementary Table S1) with identification not confirmed but judged likely to be this species.

FIGURE 27. Pleojassa multidentata (Schellenberg, 1931). Male, 8.0 mm and male 1, 7.4 mm. South Georgia, Swedish Antarctic Expedition (1901–1903), collection date and collector unknown, MfN 22.962. Male 2, paralectotype, 3.7 mm and adult female, lectotype, 7.7 mm. South Georgia, 1883, Deutsche Polar Commission, K. von den Steinen, coll., ZMH K-8028. Setae are omitted from the gnathopod 2 profiles of the male 1 and male 2. All views lateral. Scale 0.1 mm.

FIGURE 28. Pleojassa orientalis n. sp. Holotype, adult female, 9.8 mm and male, paratype, ~6.5 mm (full length estimated from comparison with the female as body posterior to segment 4 missing). Southeast corner of Gorilla Head Rock, Macquarie Island, Australia (54°29ʹS, 158°58ʹE), 23 December 1977, J. K. Lowry, coll., AM P.34955, station no. MA-147. Setae are omitted from the male gnathopod 2 profile. All views lateral. Scale 0.1 mm.