Pseudambasia sheardi, Kilgallen, N. M. & Lowry, J. K., 2013

Kilgallen, N. M. & Lowry, J. K., 2013, The lysianassid genus Pseudambasia in Australian waters (Crustacea, Amphipoda, Lysianassidae, Lysianassinae), Zootaxa 3710 (4), pp. 301-321 : 313-318

Pseudambasia sheardi sp. nov.

( Figs 12 , 13 )

Type material. Holotype, male, 3.3 mm, AM P.68867, Corny Point to Pandalowie, Spencer Gulf, South Australia (34°54'S 137°01'E), 36.5 m, K. Sheard, 14 March 1938.

Additional material examined. 1 specimen, sex unknown, 2.5 mm, AM P.68862, south east side of Gabo Island, below lighthouse, Victoria (37º34’S 149º55’E), 15-18 m, P.A. Hutchings, 15 February 1973; 2 specimens, AM P.68863, Joes Bight, Freycinet Peninsula, Tasmania (42º16’42”S 148º18’42”E), sponges, 15-17 m, R.T. Springthorpe and S.J. Keable, 1 May 1991; 10 specimens, AM P.68864, Joes Bight, Freycinet Peninsula, Tasmania (42º16’42”S 148º18’42”E), sandy boulder surface, 17 m, R.T. Springthorpe and S.J. Keable, 1 May 1991; 1 specimen, 2.9 mm, AM P.68943, Joes Bight, Freycinet Peninsula, Tasmania (42º16’42”S 148º18’42”E), 17 m, R.T. Springthorpe and S.J. Keable, 1 May 1991; 1 specimen, 2.9 mm, AM P. 83721, 450 m off Weatherhead, Freycinet Peninsula, Tasmania (42°14'S 148°14'42"E), baited trap, 15 m, J.K. Lowry & S.J. Keable, 30 April – 1 May 1991.

Type locality. Corny Point to Pandalowie, Spencer Gulf, South Australia (34°54'S 137°01'E).

Etymology. Named for Keith Sheard, the collector.

Diagnostic description. Based on holotype, male, 3.3 mm, AM P.68867. Head lateral cephalic lobe broad, subacute; eyes round. Antenna 1 short; peduncular article 1 short, length 1.2 × breadth, with distinct dorsal lobe; peduncular article 2 short, 0.2 × article 1; peduncular article 3 short, 0.2 × article 1; accessory flagellum short, 0.33 × primary flagellum, 2-articulate, article 1 short, 1.25 × article 2; primary flagellum 8-articulate, with weak 1-field callynophore, with aesthetascs on most flagellar articles. Antenna 2 flagellum 5-articulate. Mandible accessory setal row with 4 setae, the distal-most seta multiserrate; molar reduced, represented by finely setose triangular flap; palp attached proximally; article 1 long, length 2.5 × breadth; article 3 slender, blade-like, tapering into a long flagellate-like tip. Maxilla 1 outer plate broad, with 11 setal teeth, setal teeth of outer row with cusps in 1 row; palp 2-articulate, with apical slender setae. Maxilla 2 inner and outer plates broad; inner plate length 1 × outer plate. Labium outer lobe unknown. Maxilliped inner plate distal margin serrate with apical nodular robust seta.

Gnathopod 1 weakly subchelate; coxa anterior margin straight, anteroventral corner rounded, posterior margin straight; carpus short, length 1.8 × breadth, subequal in length to propodus; propodus subtriangular, length 1.7 × breadth, palm extremely acute, margin rugose to serrate. Gnathopod 2 minutely subchelate; carpus long, length 3.3 × breadth; palm transverse, with slightly sinusoidal margin. Pereopod 5 coxa bilobate, anterior lobe slightly produced ventrally. Pereopod 6 coxa with small, narrow posterior lobe; basis posterodistal corner slightly produced beyond ischium, forming rounded lobe. Pereopod 7 basis posterodistal margin oblique, posterodistal corner moderately produced, forming lobe produced halfway along merus; merus moderately expanded posteriorly.

Epimeron 3 posterodistal corner minutely notched. Uropod 1 rami subequal in length. Uropod 2 outer ramus slightly longer than inner ramus; inner ramus with moderate constriction. Uropod 3 peduncle short, without dorsolateral flange; rami slender. Telson longer than broad, length 1.25 × breadth, lateral margins rounded, apical margin slightly rounded.

Remarks. Pseudambasia sheardi differs from all other species in the genus because of the well-developed anterodistal lobe on peduncular article 1 of antenna 1. It has a minutely notched posteroventral corner on epimeron 3, similar to P. acuticaudata from New Caledonia, Papua New Guinea and the Great Barrier Reef and P. indentata from Madagascar. Pseudambasia sheardi also has a slightly tapering telson with a broad distal margin similar to P. dartnalli and P. l o c h i.

Some of the specimens collected from Joes Bight (AM P.68864) off the Freycinet Peninsula displayed a distinct chocolate-brown solid colouration across the head, pereonites and pleonites, and coxae of pereopods 1–3 and pereopod 7. Not all specimens from Joes Bight exhibited this colour pattern, nor did any specimens from other locations, therefore we cannot speculate on its significance.

Distribution. Spencer Gulf, South Australia; Gabo Island, Victoria; Freycinet Peninsula, Tasmania.

Figures

FIGURE 12. Pseudambasia sheardi sp. nov., holotype, male, 3.3 mm, AM P. 68867, Spencer Gulf, South Australia. Scale bars: 0.1 mm.

FIGURE 13. Pseudambasia sheardi sp. nov., holotype, male, 3.3 mm, AM P. 68867, Spencer Gulf, South Australia. Scale bars: G 1 - 2 and P 3 - 7, 0.2 mm; U 1 - 3 and T, 0.1 mm.