Cryptodromia pitiensis, Mclay, 2001

Mclay, Colin L., 2001, Dynomenidae and Dromiidae (Decapoda, Brachyura) from Guam, Philippine Islands, Tonga and Samoa, Zoosystema 23 (4), pp. 807-856 : 829-832

Cryptodromia pitiensis n. sp.

( Figs 5 ; 6 )

TYPE MATERIAL. — Holotype (ovig.) 17.8 × 14.2 mm, from Piti Reef , Guam ( GUM290 ) ( MNHN-B27303 ); paratype 13.2 × 11.1 mm, South of Orote Point, Guam ( GUM 296 ) ( ZRC2000.2111 ).

MATERIAL EXAMINED. — Guam. South of Orote Point, 13°27’N, 144°47’E, 18-30 m, outer reef slope, 20.XII.1990, coll. G. Nelson & H. T. Conley, 1 (ovig.) 17.8 × 14.2 mm ( GUM 290). — South of Orote Point, 18-30 m, among rocks, 15.X.1993, coll. H. T. Conley & C. Thomas, 1 13.2 × 11.1 mm ( GUM 296) ( ZRC 2000.2111).

ETYMOLOGY. — The specific name refers to the type locality, Piti Reef, Guam.

SIZE. — Type ovigerous female specimen 17.8 × 14.2 mm. Paratype male 13.2 × 11.1 mm.

DEPTH AND HABITAT. — Type and paratype specimens collected from Piti Reef, 18- 30 m.

DISTRIBUTION. — Only known from the type locality on Guam, North Pacific Ocean.

DESCRIPTION

Carapace surface mostly smooth, wider than long, cw/cl= 1.25, convex, areolate, covered with short setae which enhance areolae and subdivi- sion of carapace into areas. Frontal groove wellmarked, posteriorly dividing and surrounding gastric region. Behind gastric region two prominent grooves crossing mid-line: first groove (cervical) begins at small pit near mid-line and curves diagonally across carapace towards second and third anterolateral teeth, while second groove (marking beginning of cardiac region) divides into an anterior branch that meets cervical groove and a posterior branch that runs back to branchial groove. Gastric and cardiac regions swollen. Branchial area with four swellings, two posterior to cervical groove and two smaller swellings anterior to groove. These swellings give carapace a characteristic areolate appearance. Most of carapace surface smooth but some small scattered tubercles, especially just behind supraorbital margin, where one branchial swelling bears larger tubercle. Rostrum tridentate, teeth prominent, subacute and similar length, median tooth on lower level, deflexed but clearly visible in dorsal view; lateral teeth directed almost vertically and separated by wide U-shaped sinus. Anterolateral margin begins at level of suborbital margin, evenly convex, armed with three welldefined, evenly spaced teeth. Branchial notch

B

A

B, C

distinct and followed by posterolateral tooth slightly smaller than anterolateral teeth. Posterolateral carapace margins convergent and posterior margin slightly concave.

Supraorbital margin continues from base of lateral rostral tooth to postorbital corner where it is separated from suborbital margin by deep notch. On left-hand side small tooth interrupts supraorbital margin but this is not present on righthand side. Eyes exposed dorsally even when retracted. Suborbital margin bears one strong tooth visible dorsally and another smaller tooth at its inner border.

First article of antennae wider than long, beaked medially, upper lobe longer, curved. Second article longer than wide, prominent distal medial tubercle, distomedial margin produced on which third article is inserted at an angle. Exopod fixed, tip bilobed, curving over base of eyestalk forming inner border of orbit. Ratio of flagella length to cw= 0.55.

Subhepatic area convex, with large tooth visible dorsally, lying between large suborbital tooth and first anterolateral tooth. Inner margin of third maxilliped merus serrated, palp, setose, exposed, as long as merus plus one-third of basis. Crista dentata on mxp3 consists of eight or nine evenly spaced, blunt teeth, increasing in size distally. Female sternal sutures 7/8 end apart just behind bases of first walking legs.

Pereopods covered with short tomentum and fringed with longer setae. Chelipeds without an epipod. In female, chelipeds about as long as first two pairs of walking legs, longer in male. Merus trigonal in section, margins bearing small tubercles, outer distal surface notched. Carpus outer surface has two rounded proximal swellings and two larger swellings near distal end. Several scattered tubercles on superior surface of carpus and row of three tubercles on inner margin. Surface of propodus smooth except for two or three small tubercles on inner superior margin as well as two larger tubercles on superior face of propodus. Fingers straight, gaping, fixed finger with seven teeth increasing in size distally, margin of dactyl with one large proximal tooth (in male) followed by seven teeth as on fixed finger. Last three teeth on both fingers interlocking. Teeth more strongly developed in male.

In female, p2 and p3 about same length as chelipeds, in male shorter than chelipeds. Distal margins of meri, carpi and propodi produced as two lobes, inner margins of dactyli armed with five or six short spines increasing in size distally.

P4 and p5 reduced, both about same length, dactyli strongly curved. In female, dactyli opposed by single propodal spines, with p5 having an additional spine on outer propodal margin. P5 subdorsal, when extended forwards almost reaching a line connecting last pair of anterolateral teeth. In male paratype, p4 same as female, but p5 dactyli opposed by two unequal propodal spines.

Abdomen of six free segments, telson much wider than long, posterior margin truncate. Uniramous pleopod on first abdominal segment of female. Uropod plates large, visible externally, in male uropods used in abdominal locking mechanism by fitting in front of serrated flange on coxae of p2.

First male pleopod setose at tip, second pleopod simple, needle-like and as long as first.

DISCUSSION

Using the key to genera in McLay (1993: 123) to identify this new species, the important characters for arriving at the genus Cryptodromia are: carapace smooth, as wide or wider than long, rostrum tridentate, female sternal sutures 7/8 end apart, cheliped without an epipod, no spine on outer margin of p5 dactyl, last two abdominal segments not fused, and uropod plates on the abdomen visible externally. In using this generic key it is necessary to make allowance for the presence of scattered tubercles on the carapace of the new species. If the carapace is treated as though it had a granular surface (couplet 16 in the key) the alternative genus would be Epigodromia McLay, 1993 . The main features, which separate the species of Cryptodromia and Epigodromia , are the more granular, often areolate, carapace surface and highly reduced p4 and p 5 in Epigodromia . The difference between the p4 and p5 is associat- ed with the fact that, while sponges and ascidians are normally carried by species of Cryptodromia , none of the species of Epigodromia are known to carry camouflage. Thus C. pitiensis n. sp. has some features which make it intermediate between these two genera, but the chief reason for placing it in Cryptodromia is the fact that the p4 and p5 are comparatively well-developed and clearly equipped for bearing camouflage. The closest species to C. pitiensis n. sp. is another new species that has been described from French Polynesia (McLay 2001).

Interesting features of Cryptodromia pitiensis n. sp. are the areolate carapace surface and the presence of a pair of well-marked grooves crossing the mid-line anterior to the cardiac region. The areolae are enhanced by setae as in Dromia wilsoni (Fulton & Grant, 1902) . Similar grooves are usually found among the Dynomenidae , especially in Dynomene and Metadynomene . Arguments in favour of regarding the Dynomenidae and the Dromiidae as sister groups are given by McLay (1999: 462-467).

The holotype female was carrying about 580 eggs, diameter 0.58 mm. This egg size indicates that we should expect to find that C. pitiensis n. sp. has a planktonic larval stage as found in C. hilgendorfi (see McLay 1982). The number of eggs and egg diameter of C. pitiensis n. sp. is slightly smaller than that found in comparably sized C. hilgendorfi .

Figures

FIG. 5. — Cryptodromia pitiensis n. sp., Guam, Piti Reef, 18-30 m, holotype 17.8 × 14.2 mm; A, dorsal view of right half of carapace; B, outer face of right cheliped; C, dorsal view of right cheliped (MNHN-B27303). Setae omitted. Scale bars: A, 3 mm; B, C, 2 mm.

FIG. 6. — Cryptodromia pitiensis n. sp., 17.8 × 14.2 mm, holotype, Guam, Piti Reef, 18-30 m (MNHN-B27303); A, dorsal view of whole crab, setae intact, right fourth leg not shown; B, frontal view of the crab. Scale bars: A, 4 mm; B, 3 mm.