The sentinel crabs of the genus Chaenostoma (Stimpson, 1858) (Crustacea: Brachyura: Macrophthalmidae), with description of a new species and new records Author Naderloo, Reza text Journal of Natural History 2013 2013-09-05 47 45 - 46 2835 2848 http://dx.doi.org/10.1080/00222933.2013.807948 journal article 55792 10.1080/00222933.2013.807948 585675a5-0353-44d1-9c9a-866b2a0e8205 1464-5262 5198062 Chaenostoma lisae ( Poupin and Bouchard, 2010 ) ( Figures 3A–H , 4A–D ) Macrophthalmus ( Chaenostoma ) lisae Poupin and Bouchard, 2010 , 62, figures 1A–C, 2A–O. Material examined Indian Ocean . 2♂ (CL 4.14–4.39 mm , CB 5.26–5.59 mm ), 1♀ ovig. (CL 5.04 mm , CB 6.34 mm ) ( MNHN-B10717 ), Nosy Be , Madagascar , February 1962 , A. Crosnier; 2♂ (CL 4.66– 4.05 mm , CB 3.67– 3.17 mm ) ( MNHN ); Mozambique Channel , Europa I. BioReCIE Expedition , St. 4, outer reef, high intertidal, 8 November 2011 , J. Poupin . Pacific . 1♂ (CL 4.50 mm , CB 5.69 mm ), 1♀ ovig. (CL 5.16 mm , CB 6.79 mm ) ( MNHN ), Pindai , New Caledonia . Diagnosis Carapace sub-rectangular ( Figure 3A ), about 1.26 times as broad as long, maximum width between second lateral teeth; posterior surface with very small granules, invisible with naked eyes, granules slightly large on lateral regions. Frontal region ( Figure 3A ) deflexed downwards, densely covered with small granules; front wide, slightly less than 1/4 as wide as carapace width, slightly constricted medially; anterior edge finely dentate in middle part, slightly concave medially, nearly bi-lobed. Eyestalks ( Figure 3A ) relatively stout, short, distinctly longer than front, reaching to end of exorbital angle, very small granules on posterior surface of eyestalks. Lateral margin ( Figure 3A ) with three teeth (including exorbital angle); first one (exorbital angle) relatively subquadrate; second about as long as first, lower than first; third very small, but distinguishable, usually indicated by few granules; posterolateral margin straight, finely granulate, granules small, round, wide-based. Figure 3. Chaenostoma lisae ( Poupin and Bouchard, 2010 ) . Male (MNHN-B10717). (A) Carapace; (B) inner surface of male cheliped (inner face); (C) palm of right cheliped (outer face); (D) palm of right cheliped (inner face); (E) G1, right (ventral face); (F) apical part of the same G1 (lateral face); (G) apical part of the same G1 (ventral face). Figure 4. Chaenostoma lisae ( Poupin and Bouchard, 2010 ) . Male (MNHN-B10717) (B), and female (MNHN) (A, C–E). (A) Female right cheliped (outer face); (B) penultimate segment and telson of male abdomen; (C) female gonopore; (D) female gonopore in closer view; (E) penultimate segment and telson of female abdomen. Third maxillipeds with large gap between. Ischium slightly longer than merus, about 1.2 times as long as merus; merus quadrate. Posteromedian margin of epistome straight, median part of anterior buccal cavity smooth, without any ridge. Chelipeds ( Figure 3C, D ) nearly equal. Merus ( Figure 3B ) upper surface smooth, without plectrum ridge; upper inner margin with small granules, distally getting slightly larger; lower inner margin with small granules; outer margin denticulate. Palm ( Figure 3C ) relatively swollen, not long, about 1.2 times as long as high; outer surface ( Figure 3C ) smooth to naked eyes, microscopic granules covering whole outer surface, continuous to lower and upper margins, longitudinal ridge near lower portion, running from near tip of immovable finger backward, subparallel to lower margin, finely granular; lower margin granular, proximally bulged, not deflexed near immovable finger; upper margin slightly arched, finely granular; inner surface ( Figure 3D ) mostly covered with long setae except on marginal portions, setal patch continuous to proximal of fingers. Movable finger gently curved downward, curved inward distally, upper margin granular along proximal two third; cutting edge with subproximal differentiated tooth, long, low, two or three small denticles distal to large tooth. Immovable finger short, nearly straight, without differentiated tooth, tuberculate teeth along entire it, getting larger distally. Chelipeds of female ( Figure 4A ) small; palm nearly flat, inferior ridge prominent, subparallel to lower margin, gently curving medially, granulate, granules small distally; short longitudinal row of granules on middle portion, depressed above this ridge; upper margin with two rows of small granules; inner surface of palm smooth, row of long setae near upper margin. Fingers narrow, movable finger about as long as palm, long setae along inner surface, longitudinal ridge along outer surface, cutting edge of fingers smooth, distinct round teeth on middle part of both fingers, close to chitinous part. Walking legs medium-sized, third leg largest, fourth leg smallest, long setae scarcely along anterior margin of segments, except dactylus. Merus posterior surface smooth; anterior, posterior margins serrate, merus of second and third legs with very small subdistal tooth on anterior margin, merus of third leg slightly more than twice as long as wide. Carpus serrate on anterior, posterior margins; carpus of third leg slightly shorter than propodus. Propodus finely serrate on anterior, posterior margins, slightly longer than dactylus, that of last leg about as long as dactylus. Dactylus with scarce short setae on proximal portion, with six longitudinal smooth ridges. Male abdomen long; segments 3, 4 nearly in same length, segment 5 distinctly longer than segments 3, 4, nearly as long as segment 6; segment 6 ( Figure 4B ) with lateral margins arched, very slightly swollen proximally, converging distally; telson slightly shorter than segment 6, margins nearly sharply converging proximally, rounded apically. G1 gently curved medially ( Figure 3E ); apical chitinous process short, directed laterally at 60 ◦ ( Figure 3F, G ), lateral surface of apical process distinctly depressed, concave on apical surface, with distal margin slightly concave; long setae around apical process, long feather-shaped setae along ventral margin, short feather-shaped setae along mesial margin. Female gonopore ( Figure 4C ) small, with outer margin arched, nearly parallel to median line of sternum; operculum small ( Figure 4D ), directed forwards; margins of opening slightly elevated. Colour “Dorsal surface of carapace and appendages are white-cream scattered with brownish patches” ( Poupin & Bouchard 2010 , p. 65), which makes the species hardly distinguishable in its habitat. The preserved specimens examined here all are evenly cream-coloured. Habitat Poupin and Bouchard (2010) provided detailed information on the habitat of the species in its type locality. Chaenostoma lisae , unlike its congeners that are mainly found on rocky shores, digs burrows in the upper intertidal zone in sandy-mud habitats. Distribution Mayotte ( Comoro Islands ), Madagascar , Japan , New Caledonia . Remarks Chaenostoma lisae ( Poupin and Bouchard, 2010 ) is characterized by its blunt first anterolateral teeth of the carapace, a setal patch on the inner surface of the male cheliped palm not extending to cover inner surface of fingers, a rounded short apical process of the male G1, and a female gonopore parallel to the median line of sternum with a small operculum laterally directing forward. Regarding the blunt form of the first anterolateral teeth of the carapace, this species is readily distinguished from the type species of the genus, C . boscii (Audouin, 1926) and is similar to other congeners. Features of the male G1 of C . lisae make it completely distinct from C . boscii , C . sinuspersici (Naderloo and Türkay, 2011) and C . punctulatus ( Miers, 1884 ) , whereas it is very close to C . java n. sp. The apical process of the G 1 in C . lisae and C . java n. sp. is short, directed in anterior–posterior direction, convex on mesial surface, while that of M . sinuspersici is strongly emarginated and distinctly concave on the mesial surface (see Naderloo & Türkay 2011; Naderloo et al. 2011). The apical margin of G 1 in C . sinuspersici is distinctly two-horned, while in C . lisae it is simply slightly concave. The apical process of G 1 in C . boscii is unique by having a plate-shaped form, and being directed obliquely ventroposteriorly (see Naderloo & Türkay 2011); therefore it is not comparable with that of other species. Male chelipeds of C . lisae are not long, about 1.2 times as long as high, while those of C . boscii and C . sinuspersici are relatively long with length/height ratio about 1.5 (see Naderloo & Türkay 2011). The inner surface of the chelipeds of C . lisae has a setal patch covering the whole inner surface, but just extending to the proximal parts of fingers, but in all other congeners the setal patch extends to the end of the fingers. The female gonopore is an additional important character allowing distinction of C . lisae from both C . boscii and C . sinuspersici , the latter have female gonopores which are oblique to the central line of the sternum, and the opercula are directed posterolaterally. But in C . lisae and the new species the outer margin of the genital opening is nearly parallel to the central line of the sternum and the small opercula are directed frontolaterally. Regarding the presence and morphology of the differentiated teeth on the cutting edge of the male cheliped fingers, C . lisae is easily separated from its congeners by having a long and low tooth on the cutting edge of the movable finger, and by the absence of a gap between the fingers.