Bioacoustics of Chaenostoma sinuspersici

Remarks. Macrophthalmus sinuspersici belongs to the M . boscii -group and is closely related to M. boscii Audouin, 1825 , and M . lisae Poupin & Bouchard, 2010 . It is, however, easily distinguishable from those species using several taxonomic characters (Naderloo & Türkay 2010). Macrophthalmus sinuspersici has a distinct longitudinal stridulating ridge on the inner surface of the merus of the male cheliped, which is absent in M . boscii and M . lisae . The exorbital tooth of the carapace in M . sinuspersici and M . lisae is distinctly quadrate or semi-quadrate, terminally blunt, whereas in M . boscii it is nearly triangular and clearly directed forwards. All three species are different from each other regarding the apical part of the male G1. Macrophthalmus sinuspersici is clearly different from that of M . boscii . In M. sinuspersici the apical process of G1 is directed in an anterior-posterior direction and is strongly emarginated, with a depressed mesial surface, whereas that of M . boscii is unique with a plate-shaped apical process, being directed obliquely ventro-posteriorly. The apical process of G 1 in M . lisae is rounded, mesially convex and with an extreme depression on the lateral surface. The female gonopore of M . sinuspersici is relatively large, having a small operculum which directs obliquely lateral. In females of M . boscii , however, the operculum is remarkably large, covering most of the gonopore. A further differentiating character is a patch of setae on the inner surface of the male chelipeds. In M . sinuspersici and M . boscii , this patch continues to the inner surface of both fingers, whereas in M . lisae it is restricted to the inner surface of the palm, whereas the inner surface of the fingers is glabrous. Macrophthalmus sinuspersici is widely distributed in the Indo-West Pacific, but absent from the Red Sea, where only M . boscii occurs (Naderloo & Türkay 2010). Macrophthalmus lisae is only known from its type locality on the island of Mayotte in the, western Indian Ocean ( Poupin & Bouchard 2010 ).

Diagnosis. Carapace slightly wider than long (CB/CL = 1.2); posterior surface relatively uneven, covered with small granules, no longitudinal row of granules on branchial regions; regions well defined with deep furrows. Front slightly more than 0.25 times as wide as carapace. Lateral margin ( Fig. 18 a) with three teeth including exorbital angle; exorbital angle nearly subquadrate; second slightly longer than first; third very small, but usually distinguishable. Chelipeds ( Figs. 18 b, c) nearly equal, subequal or even unequal. Merus ( Fig. 18 d) with upper surface smooth, short stridulating ridge near inner margin, easily distinguishable by its brown colour, incompletely concealed by long setae. Palm relatively long, about 1.5 times as long as high in distal portion; inner surface mostly covered with patch of long setae, patch of setae continuous to end of fingers; cutting edge of movable fingers subproximally with large subquadrate differentiated tooth. Male G1 with apical chitinous process short, directed laterally at 45° ( Fig. 18 g), distal margin strongly concave, mesial surface of apical part deeply depressed. Female gonopore ( Fig. 18 i) relatively small, with outer margin oblique to median line of sternum; operculum small, directed outwards.