Pseudopleonexes nexis, Peart, Rachael A., 2006

Peart, Rachael A., 2006, A revision of Pseudopleonexes Conlan, 1982 (Crustacea: Amphipoda: Ampithoidae) with description of three new species from Australia, Zootaxa 1344, pp. 1-22 : 16-20

Pseudopleonexes nexis sp. nov.

( Figs. 10–12 )

Type material. Holotype: ovigerous female, 8.0 mm, AM P51281, Cape Banks, New South Wales, Australia, 34°00’S 151°14’E, 21 December 1993, 5 m, in Ecklonia radiata canopies, N. Gallahar. Paratypes: male, 7.0 mm, AM P51279, Cape Banks, New South Wales, Australia, 34°00’S 151°14’E, 20 January 1996, 5 m, in Ecklonia radiata canopies, N. Gallahar; male, 7.0 mm, AM P51280, Cape Banks, New South Wales, Australia, 34°00’S 151°14’E, 20 January 1996, 5 m, in Ecklonia radiata canopies, N. Gallahar; numerous males and females, 6–8 mm, AM P45462, Cape Banks, New South Wales, Australia, 34°00’S 151°14’E, 11 January 1994, 6 m, N. Gallahar.

Diagnosis. Antenna 1 longer than antenna 2 in males. Antenna 2 slender, peduncle similar to antenna 1, not densely setose on ventral margin. Maxilla 1 palp with 2 articles. Gnathopod 1 carpus subequal in length to the propodus, carpal lobe rounded, propodus narrow, palm transverse, entire, without midmedial tooth, without posterodistal tooth defining palm; dactylus overreaching palm. Gnathopod 2 with long dense, plumose setae on margins; carpus longer than merus, shorter than propodus; propodus broad, ovoid, not produced into an anterodistally setose lobe; palm acute, entire, without midmedial tooth, with small subacute posterodistal tooth defining palm; dactylus subequal in length to palm. Pereopod 5 merus ovoid, distal articles broad. Pereopod 6 distal articles slender. Pereopod 7 distal articles slender. Uropod 3 peduncle without distal robust setae.

Description. Based on holotype female, 8.0 mm, AM P51281. Head. Epistome and upper lip directed posteriorly at more than 45 degrees. Antenna 1 shorter than antenna 2; peduncular article 1 longer than article 2 (1.4 x), article 2 longer than article 3 (2.6 x), article 3 shorter than article 1 (0.3 x); accessory flagellum absent. Antenna 2 slender, similar to antenna 1; not densely setose on ventral margin; peduncular article 4 subequal in length to article 5; flagellum with 14 articles. Mandible molar well developed, triturating; palp with three articles, slender, long, apically setose; article 1 shorter than article 2 (0.8 x), article 2 longer than article 3 (1.2 x), article 3 subequal in length to article 1 (1 x). Upper lip distally setose, lateral margins each with a midlateral notch. Lower lip outer plate notched, with medial and lateral lobes equal in size; mandibular lobe with curved margins, subacute apically. Maxilla 1 palp with 2 articles, with apical slender setae. Maxilla 2 inner plate narrow, outer plate broader.

Pereon. Gnathopod 1 smaller than gnathopod 2, without densely setose margins; coxa smaller than gnathopod 2 coxa; coxa without setal fringe, not produced anteroventrally; carpus posterior margin not lobate, rounded, shorter than propodus (0.9 x); propodus narrow (length 2.1 x width); palm transverse, entire, without midmedial tooth, without posterodistal tooth defining palm; dactylus overreaching palm. Gnathopod 2 without densely setose margins; coxa without setal fringe; carpus shorter than propodus (0.7 x); propodus broad (length 1.2 x width), not produced into an anterodistally setose lobe; palm acute, entire, without midmedial tooth, with small subacute posterodistal tooth defining palm; dactylus overreaching palm. Pereopod 3 basis expanded; merus anteriorly expanded. Pereopod 4 basis and merus similar in shape to pereopod 3. Pereopods 5–7 strongly prehensile. Pereopod 5 broad, propodus strongly expanded distally. Pereopod 6 slender; basis posterior margin rounded proximally, straight distally; propodus strongly expanded distally. Pereopod 7 slender.

Pleon. Epimeron 3 posteroventral corner broadly rounded. Uropod 1 peduncle reaching to the middle of the peduncle of uropod 2 (in situ); rami subequal in length. Uropod 2 peduncle with broad, rounded laterodistal projection; rami subequal in length. Uropod 3 peduncle longer than broad (1.5 x), peduncle long (4 x rami length); outer ramus subequal in length to inner ramus, with two large recurved robust setae, with a lateral patch of denticles. Telson distally truncate; apical cusps expanded into large hooks.

Male (sexually dimorphic characters). Based on paratype male, 7.0 mm, AM P51279. Antenna 1 longer than antenna 2; peduncular article 1 longer than article 2 (1.3 x), article 2 longer than article 3 (2.4 x), article 3 shorter than article 1 (0.3 x). Antenna 2 peduncular article 4 shorter than article 5; flagellum with 14 articles. Gnathopod 1 smaller than gnathopod 2, without densely setose margins; coxa smaller than gnathopod 2 coxa, without setal fringe, not produced anterodistally; carpus posterior margin not lobate, rounded, subequal in length to propodus (1 x); propodus narrow; palm transverse, entire, without midmedial tooth, without defining posterodistal tooth; dactylus overreaching palm. Gnathopod 2 with long dense plumose setae on margins; coxa without setal fringe; carpus shorter than propodus (0.7 x); propodus broad, not produced to form an anterodistal lobe; palm acute, entire, without midmedial tooth, with small subacute posterodistal tooth defining palm; dactylus subequal in length to palm.

Etymology. Derived from the Greek, nexis , swimming.

Remarks. Pseudopleonexes nexis sp. nov. is similar to P. justi and P. lessoniae . It differs from P. lessoniae in the structure of antenna 2 ( P. nexis has a slender antenna 2, whereas P. lessoniae has a robust, expanded antenna 2) and in the structure of the gnathopods. In P. n e x i s, gnathopod 1 is sexually dimorphic and the carpus has a rounded posterodistal lobe. In P. lessoniae , gnathopod 1 is not sexually dimorphic, the carpus is not lobate and the posterodistal margin is straight. Pereopods 5–7 also increase in length in P. nexis with pereopod 7 the longest. Pseudopleonexes nexis differs from P. j u s t i primarily by the presence of an anterodistally produced setose lobe on the gnathopod 2 propodus on P. justi which is absent on P. n e x i s. Other characters distinguishing the two species are the relative lengths of antenna 1 and antenna 2 (antenna 1 longer than antenna 2 in P. n e x i s and shorter than antenna 2 in P. j u s t i) and the absence of a distal robust seta on the peduncle of uropod 3.

Habitat. The canopy of the brown macroalga Ecklonia radiata in shallow water.

Distribution. Cape Banks, New South Wales, Australia.

Figures

FIGURE 10. Pseudopleonexes nexis sp. nov., holotype, female, AM P 51281, 8.0 mm. Paratype, male, AM P 51279, 7.0 mm. Cape Banks, New South Wales, Australia.

FIGURE 11. Pseudopleonexes nexis sp. nov., holotype, female, AM P 51281, 8.0 mm. Paratype, male, AM P 51279, 7.0 mm. Cape Banks, New South Wales, Australia. Scales represent 0.2 mm.

FIGURE 12. Pseudopleonexes nexis sp. nov. holotype, female, AM P 51281, 8.0 mm. Paratype, male, AM P 51279, 7.0 mm. Cape Banks, New South Wales, Australia. Scales represent 0.5 mm.