Bioacoustics of Macrophthalmus (Mareotis) purpureocheir

Description. Carapace ( Fig. 3 A) 1.24 times wider than long, with scattered granules, smooth centrally, sparse setae on branchial, hepatic regions, densest laterally; central furrows deep, with scattered granules, sparse setae. First anterolateral teeth large, triangular, extended forward, separated from second tooth by wide V-shaped incision. Second anterolateral tooth large, subrectangular, anterior margin straight slightly, almost covered with long thick setae. Largest carapace width on posterior part of posterolateral margin. Front broad, slightly constricted between bases of eyestalks; margin smooth, with scattered granules near margin, anterior margin straight or slightly bilobed, with deep, narrow median furrow. Eyestalks stout, short; cornea extending to base of first anterolateral tooth. Lower orbital border regularly serrated by granules. Lower margin of epistome straight. Merus, ischium of third maxilliped concaved centrally. Third maxillipeds separated by median hiatus, not completely covering buccal cavity when closed. Cheliped ( Fig. 3 B) medium-sized, inner margin of merus without stridulatory apparatus, completely obscured by long thick setae. Palm with inner surface covered with setae; outer face covered minutely granules, near lower margin fringed with series of small granules extending to immovable finger. Dactylus slightly deflexed, armed with big differentiated tooth on cutting edge, with dentition on margin. Cutting edge of immovable finger almost covered by setae, with small tuberculate teeth on distant end. Ambulatory legs relatively stout; dactylus nearly equal to propodus; merus, carpus, propodus with long fine setae on upper, lower margins; merus elongated, without subdistal tooth. Male abdomen ( Fig. 3 C) moderately narrow; third somite without transverse ridge, lateral margins of sixth somite slightly sinuous or smooth, distal margin of telson arched. G1 ( Fig. 3 D–I) with apical chitinous process relatively short, curved, directed laterally at 90°, genital opening distally on lateral surface of apical process. Females similar to males in all non-sexual characters. Chelipeds smaller than in males ( Fig. 3 J), palm length equal to finger; distal end of fingers with long setae on cutting edge; upper half of inner surface of palm with long setae, outer surface granular, with short setae. Abdomen wide ( Fig. 3 K), third somite without transverse ridge. Female gonopore with semiellipsoidal operculum ( Fig. 3 L), directed mesially, projecting slightly; shallow depression on sternite mesial to operculum. Coloration. The carapace ( Fig. 4 A–D) is marked with patches mixed with pale yellow and greenish brown, center of carapace with a large dark patch, and posterior part with several white patches. Legs are mottled with white and pale brown. The coloration is similar to that of the habitat, which provides a useful camouflage for this species in the field. A newly molted individual had patches mixed with green and dark brown on the carapace and legs ( Fig. 4 E, F).

Remarks. This species is characterized by its reddish purple on the whole surface of cheliped, especially the male, even for fresh preserved specimens. The purple becomes paler after preserved in ethanol for a long time. This new species is morphologically similar to M. crinitus and M . definitus of the subgenus Mareotis , but still can be separated by several characters. Macrophthalmus crinitus and M. definitus are 1.3 times wider than long, but about 1.2 times of the ratio for this new species. The carapace of this new species is more convex than M. crinitus and M . definitus . The front is narrower in M . definitus and M. crinitus . The first anterolateral angles of the new species protrude forwards, and more acute than M . definitus and M. crinitus . Both M. purpureocheir sp. nov. and M. crinitus have setae on the inner face of the merus, palm, and fingers of cheliped, but M. definitus have setae only on the inner face of the palm and fingers. The mature size of the new species is similar to that of M. crinitus , but smaller than M. definitus . This new species is also similar to Macrophthalmus quadratus in the morphologies of the carapace and eyestalks, but still can be separated by several characters. While this new species belongs to the subgenus Mareotis by having a lower orbital border that is regularly serrated by granules and without stridulatory apparatus on the inner margin of the chelipeds merus, M. quadratus belongs to Paramareotis by having two large triangular protuberances on the lower orbital border as well as having a stridulatory horny ridge on the inner margin of the cheliped merus ( Barnes 2010 ). Macrophthalmus quadratus are 1.3 times wider than long, but about 1.2 times of the ratio for this new species. The first anterolateral angles of M. quadratus protrude forwards and outwards, more acute than in the new species. The carapace of the new species diverging slightly posteriorly, and the posterolateral carapace of M. quadratus is subparallel. Macrophthalmus quadratus has setae only on the inner face of the palm and none on the fingers and only slightly on the merus, different to the new species (see above). The mature size of M. quadratus is smaller than the new species. The specimens of the new species also form a distinct clade, based on 16S and COI genes, different from other species, including M. crinitus and M. quadratus (see below; Fig. 11 ).