Pachynus obsolescens, Lowry & Stoddart, 2012

Lowry, J. K. & Stoddart, H. E., 2012, The Pachynidae fam. nov. (Crustacea: Amphipoda: Lysianassoidea) 3246, Zootaxa 3246 (1), pp. 1-69 : 42

Pachynus obsolescens sp. nov.

( Figs 29 , 30 )

Type material. HOLOTYPE, female, ovigerous (1 egg), 2.6 mm, MV J62407 , 24 km north-north-east of Eddystone Point , Tasmania, in eastern Bass Strait , Australia, 40°43.9'S 148°32.5'E, 56 m, muddy sand, Smith-McIntyre grab, 14 November 1981, R. Wilson, RV Tangaroa, stn BSS 163 . PARATYPES: 1 male, 2.4 mm, MV J62409 ; 2 specimens, MV J62408 ; 2 specimens, AM P.46678; same data as Holotype .

Additional material examined. 1 specimen (mouthparts lost), MV J2497 , 42 km south-west of Babel Island , Tasmania, eastern Bass Strait, Australia, 40°14.4'S 148°40.0'E, 60 m, muddy sand, Smith-McIntyre grab, 14 November 1981, R. Wilson, RV Tangaroa, stn BSS-165G .

Etymology. The specific name reflects the absence of several features in this species.

Diagnostic description. Head lateral cephalic lobe medium sized, rounded; ventral margin curved. Antenna 1 peduncular article 1 without posterodistal spine; accessory flagellum absent; flagellum with weak 1-field callynophore in female, strong 2-field callynophore in male. Mandible lacinia mobilis absent; lamina dentata absent; accessory setal row present, not on raised setose ridge; molar absent; palp attached distally; palp article 2 slender, longer than (about 1.2 x) article 3; article 3 with subparallel margins. Maxilla 1 outer plate with 7 setal-teeth in 4/3 arrangement, setal-teeth smooth; palp well developed, 2-articulate, with apical robust setae. Maxilliped inner plate small; outer plate small; palp 4-articulate, article 4 small. Gnathopod 1 chelate; ischium smaller than propodus, not swollen posteroproximally; carpus extremely compressed; propodus length about 1.5 × breadth, posterior margin well developed, palm with produced corner, corner of palm with simple robust seta; dactylus reaching to corner of palm. Gnathopod 2 propodus length more than 2 × breadth, palm minute, obtuse. Pereonite 4 without dorsal spines. Pereonite 5 without dorsal spines. Pereopod 4 coxa proximal corner of posteroventral lobe rounded; merus expanded anteriorly, produced beyond carpus. Pereopod 5 merus with posteroproximal shoulder. Pereopod 6 basis with posteroventral lobe produced beyond ischium; merus broader than long, with posteroproximal shoul- der. Pereopod 7 basis subovate, slightly longer than wide with posterior margin weakly dentate. Epimeron 3 posterior margin without projections, posteroventral corner broadly rounded. Uropod 3 biramous, inner ramus just reaching base of article 2 of outer ramus. Telson as long as broad, entire.

Remarks. Pachynus obsolescens differs from other species of Pachynus in the following ways: accessory flagellum absent; lacinia mobilis absent; maxilla 1 outer plate with only 7 setal-teeth; pereopod 4 merus produced anteroventrally beyond carpus.

Distribution. Tasmania, Australia; 56 m depth.

Figures

FIGURE 29. Pachynus obsolescens sp. nov. Holotype female, 2.6 mm, MV J62407; paratype male, 2.5 mm, MV J62409; whole animal, paratype female, 2.4 mm, MV J62408; off Eddystone Point, Tasmania, Australia. Scales represent 0.05 mm.

FIGURE 30. Pachynus obsolescens sp. nov. Holotype female, 2.6 mm, MV J62407, off Eddystone Point, Tasmania, Australia. Scales for U1-3, T represent 0.05 mm, remainder represent 0.1 mm.