Ischyroceridae * Author Just, Jean text Zootaxa 2009 2009-10-08 2260 1 463 486 https://www.biotaxa.org/Zootaxa/article/view/zootaxa.2260.1.27 journal article 10.11646/zootaxa.2260.1.27 1175-5326 10093465 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). FIGURE 1 . Coxischyrocerus rhombocoxus gen. nov., sp. nov. , holotype, male, 2.2 mm, AM P71497, Yonge Reef, Lizard Island, Great Barrier Reef. 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).