Pseudopleonexes sheardi, Just, 2002

Just, J., 2002, Review of Pseudopleonexes Conlan, 1982, With a New Species from Australia (Crustacea: Amphipoda: Ampithoidae), Records of the Australian Museum 54 (1), pp. 31-40 : 36-40

Pseudopleonexes sheardi n.sp.

Figs. 1–4

Material examined. HOLOTYPE: male, 3.5 mm, South Australia, W. R. Baker, 1910; from Sheard’s collection; Australian Museum P35088 . PARATYPES: nine specimens (including 2 adult males and 3 ovigerous females), South Australia, Yatala Harbour, Spencer Gulf , 32°45'S 137°55'E, 5 m, MV Whyalla, 8 March 1938, K. Sheard; Australian Museum P35090 and P59944 (♀ A, ovigerous, 3.1 mm); all specimens with more-or-less broken antennae and a number of pereopods lost .

Description (male). Cephalon longer than deep, lateral length, including ocular lobes, equalling first two pereonites combined, upper and lower margins nearly parallel; ocular lobes well developed, truncate; eyes present, round, (ommatidia scattered in holotype); antennal sinus shallow. Cephalon and body moderately compressed. Coxal plates 1–4 rounded rectangular, width and depth subequal, plate 5 with anterior lobe similar to plates 1–4; plates 1–4 at most with one short posteroventral seta and a few more anterior tiny setules. Pleonal sideplates rounded, plate 3 faintly produced. Habitus of antennae close to P. lessoniae ( Hurley, 1954: fig. 1); actual length of antenna 1 not known, but longer than 2. Peduncular article 4 of antenna 2 dorsally with two small knobs, each carrying a robust seta and a small simple seta; flagellum subequal to peduncular article 5 in length, with 8 articles (holotype) the proximal 2–3 of which are fused, middle 3–4 articles with distomedial rounded projection ( Fig. 4). Mouthparts: Epistome-upper lip directed strongly backwards in lateral view (see also Barnard 1972: fig. 13j) forming an angle of approximately 45 degrees with the long axis of cephalon, this line of orientation being followed also by the mandibles. Mandibles with well-developed, slender, 3-articulate palp, article 2 with 1 apical seta, article 3 with 3 subapical setae in group, apex of article narrowly produced beyond setal group into marginally setulose, apically rounded point; spine row with broad-based, curved, unilaterally dentate robust setae. Lower lip with minutely bilobate outer lobes, outer sublobation rounded. Maxilla 1, outer plate broad, its plane somewhat rotated relative to inner plate ( Hurley, 1954, described and figured the outer plate in P. lessoniae as distally tapering, which may be due to his angle of viewing a similarly rotated plate); palp 1-articulate, not much longer than broad at base, with 2 apical setae; inner plate with rounded apex and 2 (left) and 1 (right) medial setae. Maxilla 2 outer plate twice as broad as inner plate. Maxillipeds, outer plate rather slender, approximately twice as long as broad (length measured from apex to level of insertion of palp); inner plate without apical robust setae. Gnathopod 1 with article 5 approximately 1 3 longer than broad and approximately 3 4 the length of article 6; article 6 nearly twice as long as broad, palm convex, slightly oblique, defined distally by small, curved, blunt, striate robust seta and proximally by stout, normal robust seta at rounded wide angled corner. Gnathopod 2 article 2 broadly anterolobate; article 5 as long as broad, upper part of medial surface with field of long pectinate setae with strongly expanded base and even wider socket, setae orientated at right angle with surface (similar setae appear to be present in P. lessoniae Hurley, 1954 : figs. 2, 4); article 6 nearly twice as long as 5, broadly ovoid, palm oblique, slightly convex (distal half) to concave (proximal half), defined by posterior right angle and robust seta as in gnathopod 1; upper ¼ of medial surface of article densely covered with wide-socketed setae as described for article 5. Pereopods 3 and 4 with broadly expanded article 2 (width to length = 4 to 5). Pereopod 5 with article 2 as broad as long, broadly produced posterodistally; article 4 with broadly rounded posterior lobe, article ¼ wider than long. Pereopods 6 and 7 with article 2 posteriorly expanded in proximal half, distally tapering. Palm of pereopods 5–7 similar, with short nearly straight palm defined by 1 stout, normal robust seta at rounded corner, with strong, curved, blunt, striate robust seta at base of dactylus; anterior margin of article 6 otherwise without robust setae. Gills short, oval, about twice as long as broad, present on pereopods 2–6. Pleopods with a single seta only on posterior surface of peduncle; with two coupling hooks. Uropod 1 reaching 3 2 3 4 along peduncle of uropod 2; peduncle with a single dorsal seta; outer ramus about half as long as peduncle, with 1 dorsal left; r, right; ul, upper lip; *, maxilla 1 in different view, with outer plate apical robust setae omitted.

robust seta and 2 apical robust setae; inner ramus slender, cylindrical, slightly shorter than outer ramus, with 1 apical robust seta and 1 apical seta. Uropod 2 peduncle reaching beyond base of uropod 3, with 4 to 5 short, stout dorsal robust setae and bulbous distolateral lobe; rami as in uropod 1 except outer ramus with 3 apical robust setae of unequal size. Uropod 3, peduncle with a single middorsal seta, 1 to 2 dorsoapical setae and a few lateroapical setae; inner ramus with a few (1–3) apical setae. Telson in dorsal view triangular, slightly wider at base than long, lateral margins concave, apex with 2 strong, recurved hooks separated by right angled notch.

Female. Differing from male in the following points: cephalon slightly less elongate. Article 6 of gnathopod 2 less strongly ovoid, with palm less oblique; articles 5 and 6 lacking specialised, wide-socketed setae. Peduncle of uropod 2 without lateroapical projection, with fewer dorsal robust setae.

Oostegites present on gnathopod 2 and pereopods 3–5, slender oval with long curly-tipped setae.

Size. Largest male: 3.8 mm; largest female: 3.3 mm; size range of ovigerous females: 3.1–3.3 mm.

Distribution. South Australia, Spencer Gulf, shallow water.

Etymology. The species is named after the Australian carcinologist K. Sheard, who collected the bulk of the specimens.

Remarks. Pseudopleonexes sheardi n.sp. differs from P. lessoniae in the following points: outer sublobation of lower lip rounded (pointed in P. lessoniae ); gnathopods without tuft of long setae on posterior margin of article 2 (with such tuft); article 5 of gnathopod 1 one and a half times longer than deep (twice as long as deep); pereopods 3 and 4 article 2 without posteromarginal tuft of long setae (with such setae); pereopods 5–7 generally shorter and more robust, especially pereopod 5; article 4 of pereopods 5–7 without anterodistal projection (with projection); peduncle of uropod 1 without row of dorsolateral robust setae (with such setae); uropod 3, peduncle with a few scattered setae (3 to 4 groups of dorsal plumose setae), apex of inner ramus with a few simple setae (with about 9 plumose setae). Pseudopleonexes sheardi is a distinctly smaller species with largest known male <4 mm (male: 9 mm, female: 5.75 mm; Hurley, 1954). ACKNOWLEDGMENTS. The present study is part of the results obtained during 10 months field and museum work in Australia (1984) undertaken with support from the Danish Natural Sciences Research Council (SNF 11-4180), the Carlsberg Foundation, Copenhagen, and the Australian Museum, Sydney. I thank the Australian Museum for providing access to this material. I thank colleagues in New Zealand museums and collections who helped in the search for Hurley’s type material of Pleonexes lessoniae and Barnard’s material of Ampithoe (Pleonexes) lessoniae , unfortunately to no avail.