Jassaingens Pfeffer, 1888

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 : 152-153

Jassaingens Pfeffer, 1888

( Table 13 , Figs 99–101 )

Synonyms: see Conlan (1990).

Diagnosis.

Both sexes:

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

Maxilla 1: with a small cluster of setae at the base of the palp article 1.

Gnathopod 1: basis, anterolateral margin with a few to a full row of short setae along its length which may be slender or spine-like; carpus with a single or small cluster of setae at the anterodistal junction of the propodus (setae about 1/3 of anterior margin length and slightly lateral and medial).

Gnathopod 2: basis with a row of small setae along the anterolateral margin (setal lengths <10% of the basis width); carpus and propodus, setae on the anterior margin short and simple (setal length <basis width).

Pereopods 5–7: propodus expanded anteriorly.

Uropod 1: ventral peduncular spinous process underlying about 40% 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: large individuals without plumose setae on the flagellum and peduncular article 5.

Gnathopod 2: propodus, palmar defining spines produced on a ledge, present in both small and large thumbed males.

Adult female:

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

Gnathopod 2: propodus, palmsinuous.

Remarks. All of the thumbed males available for study had relatively short thumbs with the palmar defining spines present and produced on a ledge, suggesting that these spines are not lost even in the largest animals. The antenna 2 setae are long in small juveniles but shorten drastically in the adult males. The expanded propodus of pereopods 5–7 is distinctive, even in the young. This is the largest species known for the genus, with body length at maturity in the specimens available 19.6–24.1 mm for the adult (thumbed) males and 15.3–20.8 mm for the adult females.

Figures

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).

FIGURE 100. Jassa ingens (Pfeffer, 1888). Adult male, major form, 20.3 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). Adult female, 19.2 mm, NHM 723:7, Factory Cove–Berntsen Point, Signy Island, South Orkney Islands (60°42ʹS, 45°36ʹW), 15 April 1964, M. H. Thurston, coll., station 46 (1929). Agassiz trawl close inshore over boulder slopes with Desmarestia anceps, Phyllogigas grandifolius and Rhodophyceae dominant, 6–14 m depth, IZ 1989-013 (CMN). Lateral view: male uropod 3; medial views: female gnathopod 2 and uropod 3. Scale 0.1 mm.

FIGURE 101. Jassa ingens (Pfeffer, 1888). Adult male, major form, 20.3 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). Mouthparts. Frontal view: upper lip; other views medial. Scale 0.1 mm.