Hippomedon hippolyte, Kilgallen, N. M. & Lowry, J. K., 2015

Kilgallen, N. M. & Lowry, J. K., 2015, The genus Hippomedon in Australian waters (Crustacea, Amphipoda, Lysianassidae, Tryphosinae), Zootaxa 3926 (3), pp. 377-395 : 382-385

Hippomedon hippolyte sp. nov.

( Figs 5–7 )

Types. Holotype, female, 13.4 mm, AM P.71653, Tasmania, east of Fortescue Bay, north of Hippolyte Rocks (43°06.7'S 148°03.45'E), 100 m, baited trap, 17–18 April 1993, J.K. Lowry & P. Freewater, MV Tasmanian Enterprise [TAS-372]. Paratypes: 1 male, 11.8 mm, AM P.71654; 1 male, 8.5 mm. AM P.71655, both with same locality details as holotype.

Additional material examined. 226 specimens, AM P.51155; many specimens, AM P.71651; many specimens, AM P.71652, Tasmania, east of Fortescue Bay, north of Hippolyte Rocks (43°06.7'S 148°03.45'E), 100 m, baited trap, 17–18 April 1993, J.K. Lowry & P. Freewater, MV Tasmanian Enterprise [TAS-371].

Etymology. Named for the Hippolyte Rocks, a small island off eastern Tasmania, close to the type locality. Used as a noun in apposition.

Description. Based on holotype female, 13.4 mm, AM P.71653.

Head, lateral cephalic lobe rounded, apically truncated; eyes round. Antenna 1 peduncular article 1 without anterodistal lobe; article 2 without anterodistal lobe; accessory flagellum present, not forming cap, terminal article not offset; flagellum with strong 2-field callynophore, robust setae present on proximal articles; calceoli absent. Antenna 2 peduncular article 3 short; articles 3 to 5 not enlarged; calceoli absent. Labrum (epistome and upper lip) separate; epistome less produced than upper lip, straight; upper lip produced, rounded apically. Mandible molar columnar, with subcircular fully triturating surface. Maxilla 1 inner plate with 2 apical pappose setae; outer plate setal-tooth 7 present, left and right symmetrical, cuspidate along most of straight inner margin; palp distal margin with apical robust setae. Maxilliped outer plate with 4 short, slender apical robust setae.

Gnathopod 1 subchelate; coxa large, about as long as coxa 2, subrectangular with straight anterior margin; basis moderately setose along anterior margin; ischium short; carpus long, longer than propodus, without posterior lobe; propodus small, margins subparallel, sparsely setose along posterior margin, palm moderately acute, entire, straight. Gnathopod 2 propodus palm slightly acute, straight. Pereopod 4 coxa posteroventral lobe well-developed. Pereopod 5 coxa without distinct lateral ridge, basis about as long as broad, not posteroproximally excavate, posterior margin weakly serrate, posterior margin without mid-central spine, without posteroventral lobe or spine. Pereopod 7 basis posterodistally produced less than halfway along merus, not posterodistally excavate.

Epimeron 2 posteroventral corner producing small spine. Epimeron 3 posterior margin smooth, posteroventral corner subquadrate. Urosomite 1 not projecting over urosomite 2, with anterodorsal notch, straight posterodorsally. Uropod 2 rami subequal in length, inner ramus without constriction. Uropod 3 slender; peduncle without dorsolateral flange; inner and outer rami well developed, outer ramus article 2 short, with plumose setae on both rami. Telson deeply cleft, with 4 or 5 dorsal robust setae, and 1 apical robust seta on each lobe.

Sexually dimorphic characters. Based on paratypes, male, 11.8 mm, AM P.71654. Antenna 1 flagellum with strong 2-field callynophore (stronger than female), robust setae present on proximal articles; calceoli present, small. Antenna 2 flagellum long, calceoli present.

Depth range. 100 m.

Remarks. Only two other species of Hippomedon have an epimeron 3 posteroventral corner that is not produced into a spine of some form. Of those species, Hippomedon normalis ( K.H. Barnard, 1955) , known from South Africa and Madagascar (as H. rotundipleura Ledoyer, 1986 ), differs from H. hippolyte sp. nov. in having a rounded and protruding epistome, and subtriangular lateral cephalic lobes (epistome straight, lateral cephalic lobes truncated in H. hippolyte ). Hippomedon onoconotus ( Stebbing, 1908) , also from South Africa, is easily distinguished by having a vertically produced acute spine on urosomite 1.

Distribution. Australia. Known only from the type locality, near the Hippolyte Rocks, east of Fortescue Bay, Tasmania.

Figures

FIGURE 5. Hippomedon hippolyte sp. nov. female, 13.4 mm, AM P. 71653; male, 11.8 mm, AM P. 71654, both from east of Fortescue Bay, Tasmania. Scale bars: 0.2 mm.

FIGURE 6. Hippomedon hippolyte sp. nov. female, 13.4 mm, AM P. 71653, from east of Fortescue Bay, Tasmania. Scale bars: 0.5 mm.

FIGURE 7. Hippomedon hippolyte sp. nov. female, 13.4 mm, AM P. 71653; male, 11.8 mm, AM P. 71654, both from east of Fortescue Bay, Tasmania. Scale bars: 0.2 mm.