Thrombasia saros, Kilgallen & Lowry, 2014

Kilgallen, N. M. & Lowry, J. K., 2014, The Tryphosa group (Crustacea: Amphipoda: Lysianassoidea: Lysianassidae: Tryphosinae), Zootaxa 3768 (5), pp. 501-545 : 529-530

Thrombasia saros sp. nov.

( Figs 17–19 )

Types. Holotype, female, 13.5 mm, NMV J46814 , from 76 km south of Point Hicks , Victoria, Australia (38°29.33'S 149°19.98'E), 1840 m, sandy mud, fine shell, WHOI epibenthic sled, coll. G.C.B. Poore et al, RV Franklin, 26 October 1988 . Paratypes, 4 specimens (1 damaged), 5.1–10.0 mm, NMV J16318 , same collection details as holotype .

Type locality. South of Point Hicks , Victoria, Australia (38°29.33'S 149°19.98'E), 1840 m depth .

Etymology. Named for the SS Saros, the wreck of a steamship visible on the rocks at Point Hicks, Victoria; used as a noun in apposition.

Description. Based on holotype, female, 13.5 mm. Head lateral cephalic lobe subtriangular, apically subacute; eyes apparently absent. Antenna 1 accessory flagellum forming cap partially covering callynophore, 5-articulate; primary flagellum with strong 2-field callynophore; calceoli absent. Antenna 2 peduncular article 3 short; articles 3 to 5 not enlarged, with brush setae on articles 4 and 5; flagellum short, calceoli absent. Labrum, epistome and upper lip separate; epistome less produced than upper lip, very slightly concave; upper lip produced, rounded apically. Mandible molar columnar, with oval fully triturating surface; palp attached distally, article 3 with 1 proximal A3- seta. Maxilla 1 outer plate setal-tooth 7 present, left and right symmetrical, cuspidate distally; palp distal margin with apical robust setae. Maxilliped outer plate with 4 long, broad apical robust setae and 2 long, slender apical robust setae.

Pereonites 1–7 dorsally smooth. Gnathopod 1 weakly subchelate; coxa large, about as long as coxa 2, slightly tapering distally; basis densely setose along anterior margin; ischium short; carpus long, longer than propodus, without posterior lobe; propodus small, margins tapering distally, sparsely setose along posterior margin, palm slightly acute, entire, straight. Gnathopod 2 propodus palm transverse. Pereopod 4 coxa with a welldeveloped posteroventral lobe. Pereopod 5 basis slightly longer than broad, not posteroproximally excavate, posterior margin not serrate. Pereopod 7 basis posterodistally produced not reaching merus.

Pleonite 3 without mid-dorsal carina, not produced dorsodistally, posterodorsal margin not produced. Epimeron 1 anterodistal corner produced, forming small upturned spine. Epimeron 3 posterior margin smooth, posteroventral corner rounded. Urosomite 1 not projecting over urosomite 2, dorsally straight. Uropod 2 inner ramus with strong constriction. Uropod 3 inner and outer rami well developed, outer ramus article 2 short, without plumose setae on rami. Telson m oderately cleft, with 2 dorsal robust setae per lobe and 1 apical robust setae on each lobe.

Sexually dimorphic characters. Unknown.

Habitat. Sandy mud and fine shell.

Depth range. 1840 m (this study).

Remarks. Based on the rounded posteroventral corner of epimeron 3, this species is most similar to Thrombasia rotundata and T. evalina . It is easily distinguished from these species by its longer and more weakly tapered gnathopod 1 coxa, by the propodus which is distinctly narrower than the carpus, and by the poorly defined palm.

Distribution. Bass Strait. Off the coast of Victoria, Australia (this study).

Figures

FIGURE 17. Thrombasia saros sp. nov., holotype, female, habitus, 13.5 mm, NMV J46814, from 76 km south of Point Hicks, Victoria, Australia.

FIGURE 18. Thrombasia saros sp. nov., holotype, female, 13.5 mm, NMV J46814, from 76 km south of Point Hicks, Victoria, Australia. Scale bars: 0.2 mm.

FIGURE 19. Thrombasia saros sp. nov., holotype, female, 13.5 mm, NMV J46814, from 76 km south of Point Hicks, Victoria, Australia. Scale bars: 0.5 mm.