Jassajusti Conlan, 1990

Conlan, Kathleen E., Desiderato, Andrea & Beermann, Jan, 2021, Jassa (Crustacea: Amphipoda): a new morphological and molecular assessment of the genus, Zootaxa 4939 (1), pp. 1-191 : 143-144

Jassajusti Conlan, 1990

( Table 13 , Fig. 92 )

Diagnosis.

Both sexes:

Mandibular palp: article 2, dorsal margin without a fringe of setae.

Maxilla 1: without a seta or setal cluster at the base of the palp article 1.

Gnathopod 1: basis, anterolateral margin with a fringe of short, spine-like setae; carpus without a single or cluster of setae at the anterodistal junction of the propodus.

Gnathopod 2: basis with a row of short, spine-like setae along the anterolateral margin; carpus and propodus, setae on the anterior margin short and simple (setal lengths <20% of the basis width).

Pereopods 5–7: propodus not expanded anteriorly.

Uropod 1: ventral peduncular spinous process underlying about 1/2 of the longest ramus.

Uropod 3: inner ramus without spines mid-dorsally (with only the single apical spine).

Telson: tip without apical setae (only the usual short setae at each dorsolateral cusp).

Thumbed male:

Antenna 2: without plumose setae on the flagellum and peduncular article 5.

Gnathopod 2: propodus, palmar defining spines produced on a ledge; dactyl expanded close to the junction with the propodus but not centrally toothed.

Adult female:

Antenna 2: without plumose setae on the flagellum and peduncular article 5.

Gnathopod 2: propodus, palm concave, dactyl fitting into a depression between the palm and the defining spines.

Remarks. Jassa justi shares with Jassa alonsoae , J. fenwicki , J. ingens and J. hartmannae the fringeof spine-like setae along the anterolateral margin of gnathopod 1. Gnathopod 2 sports a similar fringe. The proximal origin of the thumb in the holotype male suggests that it is a major form, in which case the pronounced palmar defining spines may be typical of all thumbed males, rather than being lost in larger major forms. This retention of the palmar defining spines by major form thumbed males would be similar to J. ingens ( Fig. 99 ), while in most species the spines are lost. Jassa hartmannae and J. kjetilanna may also retain their spines as they are similarly produced but sample size is small. There were no minor form males of J. justi available for study. Like J. fenwicki and J. ingens , the propodus spines on pereopods 5–7 are pronounced, though the propodus is differently shaped and not expanded.

Figures

FIGURE 92. Jassa justi Conlan, 1990. Holotype, adult male, major form, 8.5 mm, AM P34953; allotype, female, 6.9 mm, AM P37920; paratypes, subadult male, 5.4 mm and juvenile male 4.2 mm, AM P37921. Garden Bay, Macquarie Island (54°29ʹS, 158°58ʹE), 20 November 1977, J. K. Lowry and D. S. Horning, colls., station MA-10, among mixed red and green algae on rocky bottom, -3 m (AM). All views lateral. Setae omitted from the gnathopod 2 profiles except for those around the thumb and spines of the males in order to landmark position changes with growth. Scale 0.1 mm. Illustration after Conlan (1990).

FIGURE 99. Jassa ingens (Pfeffer, 1888). Whole body: lectotype, adult male, major form, 22.1 mm, ZMH K-8017. Moltke- Hafen, Royal Bucht, South Georgia (54°30ʹ58ʺS, 36°0ʹ45ʺW), 16 Januarly 1884, Deutsche Polarstation 1882/83, K. Von den Steinen, coll. (ZMH). Adult male 1, major form, 20.3 mm and juvenile male, 10.6 mm, NHM 1969:705:9. Billie Rocks, Signy Island, South Orkney Islands (60°42ʹS, 45°36ʹW), 5 March 1965, M. H. Thurston, coll., station 10 (97). SCUBA collection on vertical creviced rock with Lithothamnia, Desmarestia anceps, Ascoseira mirabilis, Iophon/Phyllophora, Porifera, Polyzoa, 1.9–2.2 m depth, IZ 1989-013 (CMN). Subadult male, 19.9 mm, NHM 1969:713:4. Billie Rocks, Signy Island, South Orkney Islands (60°42ʹS, 45°36ʹW), 27 February 1965, M. H. Thurston, coll., station 20 (512), SCUBA collection on rock inclined at 45–50°with overlying boulders and sand in crevices. Lithothamnia, Desmarestia anceps, Rhodophyceae, Polyzoa, 7.4–7.7 m depth (NHM). All views lateral. Setae omitted from the gnathopod 2 profiles except for those around the thumb and spines of the males in order to landmark position changes with growth. Scale 1 mm. Illustration after Conlan (1990).