Jassathurstoni 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 : 145-147

Jassathurstoni Conlan, 1990

( Table 13 , Figs 93–94 )

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 only a single short seta distally; carpus with a small cluster of moderately long setae at the anterodistal junction of the propodus (setae 25% of anterior margin length).

Gnathopod 2: basis with only a few minute setae along the anterolateral margin (setal lengths <20% of the basis width); carpus and propodus, setae on the anterior margin short and simple (setal length <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 not 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 sinuous; dactyl, inner margin evenly curved, tip fitting into depression between palmar angle and defining spines.

Remarks. Only two thumbed males of J. thurstoni were available for study, both of which were major forms. Therefore, the appearance of the minor form is unknown. Jassa thurstoni is morphologically similar to J. kjetilanna and both have been collected in the Falkland Islands. Acomparison of the two species is given in the Remarks for J. kjetilanna .

Compared to the Southern Hemisphere J. fenwicki and J. ingens , Jassa thurstoni has a slender antenna 2 without brush or plumose setae on the flagellum and the pereopods 5–7 are not modified for grasping. It also lacks the fringe of spine-like setae along the anterolateral margin of gnathopod 1, which is typical of the Southern Hemisphere species J. alonsoae , J. fenwicki , J. hartmannae , J. ingens and J. justi .Another Southern Hemisphere species that lacks the fringe, J. gruneri , differs from J. thurstoni in lacking a seta or cluster of setae at the anterodistal junction of the gnathopod 1 carpus with the propodus, while J. thurstoni possesses a setal cluster there. Jassa gruneri also possesses a short fringe of relatively long setae on the basis of gnathopod 2 while J. thurstoni lacks this fringe. Jassa thurstoni is only known from the Antarctic and sub-Antarctic islands while J. gruneri is only known from Tasmania ( Figs 11–12 ).

Figures

FIGURE 11. Records of Southern Hemisphere species of Jassa. Red dot: identification confirmed by specimen examination; green dot: literature record (Supplementary Table S1) with identification not confirmed but judged likely to be this species; blue x: suspected or known to be on the hull or interior of a boat or ship.

FIGURE 12. Records of Southern Hemisphere species of Jassa (continued). Red dot: identification confirmed by specimen examination; green dot: literature record (Supplementary Table S1) with identification not confirmed but judged likely to be this species; blue x: suspected or known to be on the hull or interior of a boat or ship.

FIGURE 93. Jassa thurstoni Conlan, 1990. Holotype, adult male, major form, 5.9 mm, NHM 1969:761:2. Paal Harbour, Signy Island, South Orkney Islands (60°43ʹS, 45°36ʹW), 5 February 1965, M. H. Thurston, coll., station 44 (1218).Anchor dredge over mud at 20–25 m depth (NHM).Adult male 1, major form, paratype, 6.0 mm, NMCC-1082. Observation Bluff, Outer Islet, Signy Island, South Orkney Islands (60°42ʹ30ʺS, 45°35ʹ10ʺW), 14 September 1965, M. H. Thurston, coll., station 52 (2085), Agassiz trawl over gravel and sand, sand with some rock, algae on rocks, 20 m depth, NHM 1969:763:1 donated to CMN, accession no. IZ 1989-013. Adult female, paratype, 6.5 mm, NHM 1969:762:3. Berntsen Point–Bare Rock, Signy Island, South Orkney Islands (60°42ʹ10ʺS, 45°35ʹ30ʺW), 16 October 1964, M. H. Thurston, coll., station 50 (AT 76). Agassiz trawl over gravel and sand, some rocks with Desmarestia anceps and Phyllogigas grandifolius, 5–10 m depth (NHM). Lateral view: whole body, antenna 1 and gnathopod magnifications; medial view: uropod 3. Setae omitted from the gnathopod 2 profiles except for those around the thumb and spines of the male 1 in order to landmark position changes with growth. Scale 0.1 mm. Illustration after Conlan (1990).

FIGURE 94. Jassa thurstoni Conlan, 1990. Adult male 1, major form, paratype, 6.0 mm, NMCC-1082. Observation Bluff, Outer Islet, Signy Island, South Orkney Islands (60°42ʹ30ʺS, 45°35ʹ10ʺW), 14 September 1965, M. H. Thurston, coll., station 52 (2085), Agassiz trawl over gravel and sand, sand with some rock, algae on rocks, 20 m depth, NHM 1969:763:1. IZ 1989-013 (CMN). Mouthparts. Frontal view: upper lip; lateral view: maxilla 1; other views medial. Scale 0.1 mm.