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.