Coxischyrocerus rhombocoxus, Just, 2009

Just, Jean, 2009, Ischyroceridae *, Zootaxa 2260 (1), pp. 463-486 : 464-466

Coxischyrocerus rhombocoxus sp. nov.

( Fig. 1 )

Type material. Holotype, male, 2.2 mm, AM P71497, Yonge Reef, Half Mile Opening (14°34'33"S 145°36'43"E), Halimeda and other algae, 10 m, C.S. Serejo, 4 March 2005 (QLD 1819).

Etymology. The epithet refers to the nearly rhomboid shape of the coxa of male gnathopod 2.

Description. Based on holotype, male; female unknown.

Head. E yes approximately 1/3 dorsal head length, situated partially within the lateral lobe of the head; lateral cephalic lobes apically acute. Antenna 1 peduncular article 1 distinctly shorter than article 3; flagellum distinctly longer than peduncular article 3, with 4 articles; accessory flagellum 2-articulate (article 2 minute). Antenna 2 short (less than 1/2 body length), peduncular articles 4–5 with 4 or more rows of setae per article; flagellum subequal to peduncular article 5, with 3 articles, proximal article longer than combined length of the two distal ones.

Pereon. Gnathopod 1 distinctly smaller than gnathopod 2; coxa 1 half length of 2 and shorter than 3 and 4; carpus distinctly shorter than propodus; propodus 1.5 x as long as wide, posterodistal margin evenly rounded. Gnathopod 2 subchelate with slender setae; coxa rhomboid, distinctly longer than wide, distally tapering, distinctly longer than coxae 1 and 3; carpus nearly 3 x as wide as long; propodus approximately 10 x longer than carpus, elongate, posterior margin basically straight, with 1 large and 1 smaller projection distally; dactylus distinctly longer than half length of propodus, with 2 humps on posterior margin. Pereopods 3–4 basis weakly expanded, almost linear; merus weakly expanded. Pereopods 5–7 basis with a few setae; pereopod 5 basis narrower than basis pereopods 6–7, with posterodistal rounded lobe, posterior margin concave; merus not expanded around carpus.

Pleon. Uropod 1 peduncle dorsolateral margin with a few robust setae. Uropod 2 peduncle dorsolateral margin without setae, with a few robust setae apically. Uropod 3 peduncle length approximately 3 x lateral greatest width, broad proximally, narrowing distally. Telson subtriangular, with single robust seta on each lateral margin.

Habitat. Among Halimeda and other algae; 10 m.

Remarks. Among Ischyrocerus species only I. inexpectatus Ruffo, 1959 (Red Sea; see also Myers 1989) shares with Coxischyrocerus rhombocoxus sp. nov. the reduced coxa 1, enlarged coxa 2, and a posterodistally lobed pereopod 5 basis with concave hind margin. That species is here transferred to Coxischyrocerus . Males of Coxischyrocerus rhombocoxus differ from those of C. inexpectatus as follows (latter in parentheses): presence of long setae ventrally on antenna 2 peduncle articles 4 and 5 (small, short setae); antenna 2 less than half body length (more than half); flagellum of antennae 1 and 2 short with 4 and 3 articles respectively (7 and 6 articles); coxa 2 anteroventrally with acute angle (rounded); propodus of gnathopod 2 10 x longer than carpus (6 x), without small thumb proximally on posterior margin (with low thumb), posterodistal projections of unequal size, proximal one larger, pointed (equal size, rounded).

Ischyrocerus parma Myers, 1995 from Madang, northern Papua New Guinea, shares with

Coxischyrocerus rhombocoxus gen. nov., sp. nov. the distinctive configuration of gnathopod 2 ischium to propodus ( Myers 1995: fig. 44 male gnathopod 2), especially the compressed merus and carpus and the large setose anterior flange on the ischium. On the other hand, coxa 2 does not seem to be particularly enlarged, and the combined description of pereopods 5–7 does not indicate a concave posterior margin of pereopod 5 basis. Pending further examination of Ischyrocerus parma , its relationship to Coxischyrocerus rhombocoxus remains unclear.

Distribution. Australia. Queensland: Lizard Island, Great Barrier Reef (current study).

Figures

FIGURE 1. Coxischyrocerus rhombocoxus gen. nov., sp. nov., holotype, male, 2.2 mm, AM P71497, Yonge Reef, Lizard Island, Great Barrier Reef.