Hippomedon tourville, 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 : 390-394

Hippomedon tourville sp. nov.

( Figs 11–14 )

Types. Holotype, female, 12.0 mm, NMV J15796 , 54 km east-north-east of Cape Tourville , Tasmania, Australia (41°57.30'S 148°58.54'E), 1770 m, coarse biogenic rubble, WHOI epibenthic sled, 30 October 1988, G.C.B. Poore et al., RV Franklin [SLOPE 82]. Paratype, male, 11.2 mm, NMV J67805 , same collection details as holotype.

Additional material examined. Tasmania. 2 specimens, NMV J67806 ; 1 specimen, NMV J67807 , 48 km east-north-east of Cape Tourville (42°00.25'S 148°43.55'E to 41°57.77'S 148°42.08'E), 1264– 1130 m, gravel with lumps of sandy mud aggregate, WHOI epibenthic sled, 30 October 1988, G.C.B. Poore et al., RV Franklin [ SLOPE 81]; 2 specimens, AM P.75735, 11 specimens, AM P.75589, North of Hill U Seamount (44°17.53'S 147°11.6'E), 1350 m, baited trap, 7 April 2007, S.J. Keable, RV Southern Surveyor [SS 02/2007/27].

Victoria. 1 male, NMV J67808 , 96 km south of Point Hicks (38°40.29'S 149°18.06'E), 2900 m, compacted clay, WHOI epibenthic sled, 25 October 1988, G.C.B. Poore et al., RV Franklin [ SLOPE 66]; 1 specimen, NMV J67809 , 67 km south of Point Hicks (38°23.95'S 149°17.02'E), 1277 m, fine mud, WHOI epibenthic sled, 25 October 1988, G.C.B. Poore et al., RV Franklin [ SLOPE 67]; 2 specimens, NMV J67810 , 76 km south of Point Hicks (38°29.33'S 149°19.98'E), 1840 m, sandy mud, fine shell, WHOI epibenthic sled, 26 October 1988, G.C.B. Poore et al., RV Franklin [ SLOPE 69].

Etymology. Named for the type locality. The name is used here as a noun in apposition.

Description. Based on holotype female, 12.0 mm, NMV J15796 .

Head, lateral cephalic lobe subtriangular, apically acute. 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 absent from proximal articles; calceoli absent. Antenna 2 peduncular article 3 short; articles 3–5 not enlarged; flagellum long, calceoli absent. Labrum (epistome and upper lip) separate; epistome produced beyond upper lip, forming thin, broadly rounded lamina; upper lip not produced. Mandible molar columnar, with oval fully triturating surface. Maxilla 1 inner plate with 1 large apical pappose seta and 6 smaller pappose setae along inner margin; outer plate setal-tooth 7 present, left and right symmetrical, cuspidate distally along inner margin; palp distal margin with apical robust setae. Maxilliped outer plate with one slender and one broad apical robust setae.

Gnathopod 1 subchelate; coxa large, about as long as coxa 2, subrectangular with straight anterior margin; basis densely 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 transverse to slightly acute, straight. Pereopod 4 coxa posteroventral lobe moderately 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 subquadrate. Epimeron 3 posterior margin smooth, posteroventral corner forming broad, upwardly curved spine. Urosomite 1 not projecting over urosomite 2, dorsally straight. 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 moderately to deeply cleft, with 2 or 3 dorsal robust setae and 1 apical robust seta on each lobe (setae apparently lost on holotype).

Sexually dimorphic characters. Based on male, 14.2 mm, NMV J67808 . Antenna 1 flagellum with strong 2- field callynophore, robust setae absent from proximal articles; calceoli present, small. Antenna 2 peduncular article 3 short; articles 3–5 not enlarged; flagellum long, calceoli present.

Depth range. 1108–2900 m.

Remarks. Morphologically, this species most closely resembles Hippomedon major ( K.H. Barnard, 1932) from South Georgia and the South Shetland Islands. Both species have a broadly rounded epistome that protrudes strongly beyond the upper lip, plumose setae lining the inner margin of the maxilla 1 inner plate, and an epimeron 3 posteroventral corner produced into a long, slender spine. The description of H. major provided by K.H. Barnard (1932) lacks detail, but from the illustrations it is noted that the posteroventral spine of the third epimeron is much broader in H. tourville sp. nov., while the urosomite 1 is dorsodistally straight, compared with the slightly rounded urosomite of H. major .

Hippomedon tourville sp. nov. is also similar to H. tasmanicus J.L. Barnard, 1961 , from the Tasman Sea, off the coast of New Zealand. However, the epistome of that species is not produced, nor is the epimeron 3 spine as strongly produced as it is in H. tourville ; the carpus of gnathopod 1 is much longer than the propodus (only slightly longer in H. tourville ); and the telson is more deeply cleft than that of H. tourville .

Distribution. Australia. Bass Strait, and eastern coast of Tasmania.

Figures

FIGURE 11. Hippomedon tourville sp. nov., male, 14.2 mm, NMV J 67808, from 96 km south of Point Hicks, Victoria.

FIGURE 12. Hippomedon tourville sp. nov., holotype female, 12.0 mm, NMV J 15796, from 54 km east-north-east of Cape Tourville, Tasmania; male, 14.2 mm, NMV J 67808, from 96 km south of Point Hicks, Victoria. Scale bars: 0.2 mm.

FIGURE 13. Hippomedon tourville sp. nov., holotype female, 12.0 mm, NMV J 15796, from 54 km east-north-east of Cape Tourville, Tasmania. Scale bars: 0.5 mm.

FIGURE 14. Hippomedon tourville sp. nov., holotype female, 12.0 mm, NMV J 15796, from 54 km east-north-east of Cape Tourville, Tasmania; male, 14.2 mm, NMV J 67808, from 96 km south of Point Hicks, Victoria. Scale bars: 0.5 mm.