Chaenostoma (Stimpson, 1858)

Naderloo, Reza, 2013, The sentinel crabs of the genus Chaenostoma (Stimpson, 1858) (Crustacea: Brachyura: Macrophthalmidae), with description of a new species and new records, Journal of Natural History 47 (45 - 46), pp. 2835-2848 : 2836-2837

Key to male specimens of the species of Chaenostoma Stimpson, 1858

1. Distinct chitinous plectrum near lower margin of inner surface of merus of male chelipeds................................... Chaenostoma sinuspersici

– Without plectrum on the upper surface of merus of male chelipeds........ 2

2. Movable finger of male cheliped without differentiated tooth; inner surface of palm with dense setal cover, not extending to inner surface of fingers................................................................ Chaenostoma lisae

– Movable finger of male cheliped with distinct differentiated tooth, inner surface of palm with dense setal cover extending along inner surface of fingers ........................................................................ 3

3. Exorbital angle acute; posterior surface of carapace uneven, mostly granulate; first male gonopod with apical process plate-shaped..... Chaenostoma boscii

– Exorbital angle relatively obtuse; posterior surface of carapace not extremely uneven, not granulate................................................... 4

4. Posterior surface of carapace with scattered small granules; apical process of first male gonopod short, rounded, directed laterally at nearly 60 ◦ ............................................................. Chaenostoma java n. sp.

– Posterior surface of carapace without granules; first male gonopod with elongate apical process........................... Chaenostoma punctulatus

Systematic account

Subsection THORACOTREMATA Guinot, 1977

Family MACROPHTHALMIDAE Dana, 1851

Chaenostoma (Stimpson, 1858)

Type species: Macrophthalmus boscii Audouin, 1826

Diagnosis

Small-sized (CL <15 mm) species; carapace slightly broader than long (CB/CL <1.3), posterior surface with scattered small granules, without granular ridges; lateral margin with three teeth, first one largest, last one smaller. Front broad, larger than 0.2 as broad as carapace in basal part of front, slightly constricted medially; eyestalks short, stout, not extending beyond exorbital teeth. Chelipeds equal; palm moderately long, about 1.5 times as long as high in its distal portion or slightly shorter, outer surface with longitudinal granular ridge parallel to lower margin, extending from tip of immovable finger backward near to articulation with carpus, inner surface with patch of dense cover of setae, setal patch may continue to inner surface of fingers; immovable finger not deflexed or very slightly deflexed; movable finger with more or less distinct differentiated proximal tooth. Walking legs medium-sized, scarcely covered with setae, without any spine, second and third ones larger, nearly of same length. Third maxillipeds relatively long, with gap between them, ischium about 1.5 times as long as quadrate-shaped merus, with circular pattern of long setae on proximal portion of outer surface. Posteromedian margin of epistome straight, median part of anterior buccal cavity smooth, without any ridge. Male G1 with small apical process and short mesial palp. Female cheliped with outer surface of palm finely granular, with distinct granular ridge, running subparallel to lower margin; cutting edge of fingers smooth; female gonopore with small operculum directing outwards.