Bioacoustics of Ilyograpsus rhizophorae

Redescription. Carapace nearly subquadrate ( Figs. 1 , 3 a), slightly wider than long (CL/CB = 1.18), maximum width between third lateral teeth; posterior surface uneven, relatively convex, regions poorly defined; 2 transverse ridges on frontal region, smooth, straight; without epigastric ridges; several transverse ridges on posterolateral region, short, oblique. Front relatively broad, about 0.4 times as wide as carapace, broadly bi-lobed, lobes slightly extending beyond inner orbital angle. Anterolateral margin with 4 distinct teeth, first (exorbital angle) largest, acute, wide triangular, directed forwards; second blunt, as long as first, slightly higher than latter; insetting between first, third teeth; third acute, triangular, highest among all teeth; fourth very small, acute; posterolateral margin nearly subparallel, converging posteriorly ( Fig. 1 ). Eyestalks moderately long, orbit slightly more than one fourth of maximum carapace width, upper orbital margin slightly sinuous; lower orbital margin of males ( Fig. 2 a) with 3, 4 long tubercles; lower orbital margin of females ( Fig. 2 b) with numerous denticles, irregular, variously-sized, larger laterally. Third maxilliped ( Fig. 2 f) with moderately large gap; ischium about 1.5 times as long as merus, with wide elevation near inner margin, short setae scarce along inner margin; merus short, much shorter than wide, with relatively narrow elevation near inner margin, short setae scarce on inner margin; exopod proximally wide, narrowing distally. Chelipeds relatively small; upper margin of merus minutely serrated, with small subdistal spine; lower inner margin finely serrated proximally, distally denticulated, slightly expanded; lower outer margin denticulate; plectrum ( Fig. 2 e) on inner surface near lower margin, distinct, short. Manus ( Fig. 2 c) about 2.4 times as long as high, slightly longer than movable finger; outer surface smooth, very small, sparse granules on upper portion; lower margin concave in middle part; inner surface smooth, patch of dense setae on distal portion, extending to proximal part of fingers. Fingers relatively narrow, long, smooth, narrow gap between fingers, wider distally; long setae along inner, outer margins of cutting edge; movable finger with cutting edge slightly elevated proximally, with small, variously-size denticles; immovable finger with small denticles on cutting edge, large ones on middle portion; tip of fingers spoon-shaped. Cheliped of females ( Fig. 2 d) narrow, long, about 3.2 times as long as high; merus with small subdistal spine on upper margin, stridulating ridge on inner surface; palm without patch of setae on inner surface; cutting edge of fingers scarcely with small denticles; gap between fingers becoming slightly wider distally. Walking legs ( Fig. 1 ) relatively long, moderately slender, flattened; second, third largest; merus with large subdistal spine, anterior margin sinuous, faintly serrate, posterior margin nearly straight, merus of fourth leg about 2.6–2.9 times as long as wide (around 2.0 in females); propodus with distal spine on posterior margin, fourth walking legs with short setae along anterior, posterior margins; dactylus narrow, long, unarmed. Male abdomen ( Fig. 2 g) moderately narrow, segments 4, 5 longest, of equal length; segment 6 about 1.75 as wide as long, lateral margin nearly straight on anterior half, converging posteriorly; telson longer than wide, slightly longer than segment 6, posteriorly rounded. Male G1 ( Figs. 2 i, j) narrow, straight, slightly curved mesially, apical process long, slightly bent laterally, with depression on lateral surface, distal opening distally on lateral surface; long setae along apical process, short setae scarce along lateral, ventral surface. Female gonopore ( Fig. 2 h) with elevated lateral lobe; operculum small, hinging on inner margin, directed outwards.