Coralliocryptus, Komai, Tomoyuki & Ng, Peter K. L., 2012

Komai, Tomoyuki & Ng, Peter K. L., 2012, A new genus and new species of leucosiid crab (Crustacea: Decapoda: Brachyura) from coral reefs in the Indo-West Pacific, Zootaxa 3352, pp. 40-50 : 40-42

Coralliocryptus n. gen.

Type species. Coralliocryptus caementa n. sp., by monotypy.

Diagnosis. Carapace distinctly wider than long, subhexagonal in general outline; dorsal surface covered with tubercles of various sizes, often stalked, but without distinct keels; frontal region slightly produced, bilobed by shallow median sulcus; cardiac region with low subconical tubercle; intestinal region with large elevation; epibranchial region strongly expanded laterally, divided into 2 lobes; pterygostomial region with prominent subconical tubercle; posterolateral margin with 1 tubercle; posterior margin with distinct tubercle at each lateral angle. Orbital hiatus effectively closed with dorsolateral angle of antennular fossa fusing with inner suborbital angle. Ocular peduncle short. Antennular basal article and flagellum folding slightly obliquely in fossa, concealed by operculiform basal article when closed. Basal antennal article positioned at lateral half of ventral floor of antennular fossa, passing under orbital margin in distal part, with distal articles and antennal flagellum inside orbit. Buccal cavern reaching beyond anterodorsal ends of afferent channel. Exopod of first and second maxilliped with flagellum. Third maxilliped with basis completely fused with ischium; merus distinctly shorter than ischium measured along mesial margin; exopod with rounded proximolateral angle. Chelipeds moderately long; merus with row of prominent stalked-tubercles on anterior and posterior margins; carpus without crests; palm gently inflated; fingers elongated, distinctly longer than palm, each with row of prominent, sharp teeth on opposable (cutting) margin. Ambulatory legs similar in shape and ornamentation; meri weakly compressed, with row of mushroom-shaped tubercles on extensor and flexor margins; carpi without crests; dactylo-propodal locking mechanism well developed. Thoracic sternum covered with numerous granules of various sizes; each suture separating sternites interrupted medially; medial suture absent; female sterno-abdominal cavity deeply excavated, well defined, completely covered by abdomen. Male abdomen narrowly triangular, consisting of free somites 1, 2 and 6, and functionally fused somites 3–5 (trace of sutures still evident on outer surface) plus telson. Female abdomen relatively narrow, consisting of 6 free somites plus telson, with first somite concealed beneath carapace; telson distinctly wider than long. G1 slender, compressed laterally, slightly sinuous in lateral view, terminating in subacute tip. G2 short, less than one-third length of G1, with foliaceus distal part.

Distribution. Widely distributed in the Indo-West Pacific, from the Comoro Is. to the Western Pacific; shallow coral reefs, 13– 30 m.

Remarks. With regards to the highly eroded carapace, Coralliocryptus n. gen. superficially resembles genera like Oreophorus , Oreotlos and Alox , but many characters argue against a close relationship. Firstly, the cheliped fingers of Coralliocryptus n. gen. are very slender and elongated with the cutting margins armed with strong spiniform teeth. In members of the latter three genera, the fingers are usually stout and stocky, and while the cutting margins may have sharp teeth, they are never spiniform (e.g., see Tan & Ng 1995: Figs. 2 E; 8C; 12C; 16B; 17D; Naruse & Ng 2006: Fig. 2 C; Galil & Ng 2007: Fig. 1 A-C; 2009: Fig. 2 C; Huang 2010: Fig. 2 D; Ng et al. 2009: Fig. 3 A). Most significantly, the female abdomen of Coralliocryptus n. gen. is unique in having all the somites and telson free, whereas all other known leucosiids have most of the somites fused to form a domed plate (e.g., see Tan & Ng 1995: Figs. 8F; 16D). However, Coralliocryptus still has a deeply excavated sterno-abdominal cavity in which the eggs are retained and are completely covered by the abdomen, as in other leucosiid taxa. As such, Coralliocryptus n. gen. should be included in the Leucosiidae as defined at present rather than in Iphiculidae Alcock, 1896 , another family placed in the Leucosioidea, in spite of the similarity in the armature of the fingers of the chelae and the freely articulated female abdominal somites between the present new taxon and the members of Iphiculidae . The primary character that defines the Iphiculidae is the relatively narrow female abdomen in which all the somites are free, the sterno-abdominal cavity is relatively shallow and the eggs are never completely covered by the abdomen, with the egg mass protruding from the sides of the abdomen (see Ng et al. 2008). It is worth mentioning that all iphiculids have the same kind of chela as that of Coralliocryptus n. gen., with slender fingers and spiniform teeth along the cutting margins. This unusual chela, however, is not unique to iphiculids, and is also seen in various leucosiids, including some species of Myra Leach, 1817 (see Galil 2001) and Nursilia Bell, 1855 (see Ihle 1918; Chen 1982).

In most species of Oreophorus , Oreotlos and Alox , the basal antennal article is tightly lodged in the orbital hiatus, fusing with it (e.g., see Tan & Ng 1995: Figs. 5 K). In Coralliocryptus , however, while the basal antennal article is still in the same position, there is no real orbital hiatus because the orbital margin is effectively closed, with the dorsolateral angle of the antennular fossa and inner suborbital angle fused together ( Fig. 3 E). The basal antennal article of Coralliocryptus is therefore, actually underneath the orbital margin ( Fig. 5 D). This is a rare feature in leucosiids but is not well studied and may be of higher systematic value. It is noteworthy that at least one Oreotlos species, O. heuretos Tan & Ng, 1995 , has an orbital structure similar to that of Coralliocryptus (H. Komatsu, pers. comm.).

Etymology. From the combination of the Latinized Greek corallium (= coral) and cryptus (hidden), in reference to the new taxon cryptic habitat and mimic habit in shallow coral reefs, having prevented its discovery until recently. Gender masculine.

Comparative material. Alox ornatum ( Ihle, 1918) : 1 male (CBM-ZC 6885), N of Yakushima I., Ohsumi Is, southwestern Japan, 30°28.00’N, 130°34.60’E, 96 m, TRV Toyoshio-maru, 1997-05 cruise, stn 11, 3 June 1997, dredge, coll. T. Komai. Alox rugosum (Stimpson, 1858) : 1 male (CBM-ZC 3999), Singapore, 15–20 m, 9 May 1997, dredge, coll. T. Komai; 1 female (CBM-ZC 9635), Red Beach, Kin, Okinawa, Ryukyu Archipelago, 4 m, 23 January 2009, SCUBA diving, coll. Yusuke Yamada. Alox uru Naruse & Ng, 2006: 1 male (CBM-ZC 7080), Uehara beach, Iriomote I., Yaeyama Is., Ryukyu Archipelago, subtidal, 8 July 2001, dip net, coll. T. Komai. Oreotlos latus (Borradaile, 1903) : 1 male (CBM-ZC 6906), off Muko-jima I., Ogasawara Is, 27°47.72’N, 142°02.97’E, 68–70 m, TRV Shin’yo-maru, 1997 cruise, stn 2, 15 October 1997, dredge, coll. T. Komai. Comparative material of Oreophorus , Oreotlos , Alox , Iphiculus and Pariphiculus species in the ZRC recorded in Tan & Ng (1995), Naruse & Ng (2006), Galil & Ng (2007, 2009), and Ng et al. (2009) are not relisted here.

Figures

FIGURE 1. Coralliocryptus caementa n. gen., n. sp., holotype, female (5.4 x 9.1 mm) (CBM-ZC 10875), Okinawa, entire animal. A, dorsal view; B, anterior (frontal) view; C, ventral view.

FIGURE 2. Coralliocryptus caementa n. gen., n. sp., non-type, male (3.8 x 6.4 mm) (CBM-ZC 10876), Vanuatu, entire animal. A, dorsal view; B, anterior (frontal) view; C, ventral view.

FIGURE 3. Coralliocryptus caementa n. gen., n. sp., holotype, female (5.4 x 9.1 mm) (CBM-ZC 10875), Okinawa. A, schematic drawing of carapace, dorsal view, showing outline and position of tubercles; B, anterior part of carapace, left side, dorsal view; C, lateral part of carapace, dorsal view; D, frontal part of carapace, right side, anterior (frontal) view, showing epistome, antennular fossa and antenna; E, right orbit, anterior (frontal) view; F, dorsal roof of orbit, posterodorsal view; G, left third maxilliped, outer view; H, anterior part of sterno-abdominal cavity, ventral view; I, abdomen and telson, ventral view (tubercles on somites 3 – 6 and telson, and setae omitted). Scale bars: 2 mm for A; 1 mm for B, C, I; 0.5 mm for D – G. Abbreviations: A 1 B, basal segment of antennule; S 1, abdominal somite 1.

FIGURE 5. Coralliocryptus caementa n. gen., n. sp., holotype, female (5.4 x 9.1 mm) (CBM-ZC 10875), Okinawa. A, right cheliped, ventral view; B, same, dorsal view (tubercles on merus omitted); C, same, chela, extensor (anterior) view; D, right first ambulatory leg (second pereopod), ventral view; E, same, dactylus, ventral view. Scale bars: 1 mm for A – D; 0.5 mm for E.