Cryptodromia pentagonalis Hilgendorf, 1879

Mclay, Colin L., 2001, Dynomenidae and Dromiidae (Decapoda, Brachyura) from Guam, Philippine Islands, Tonga and Samoa, Zoosystema 23 (4), pp. 807-856 : 835-836

Cryptodromia pentagonalis Hilgendorf, 1879

Dromia (Cryptodromia) pentagonalis Hilgendorf, 1879: 814 , pl. 2, figs 1, 2.

Cryptodromia pentagonalis – Ives 1891: 218 (list). — Henderson 1893: 406. — Ortmann 1894: 34. — Alcock 1901: 77 (list). — Lenz 1905: 363. — Nobili 1906: 146. — Rathbun 1911: 194. — Ihle 1913: 90 (list). — Balss 1934: 502. — Barnard 1950: 328 (key); 1955: 38. — Guinot 1967: 240 (list). — Lewinsohn 1977: 1; 1979: 6, text fig. 2A.; 1984: 109. — McLay 1993: 198 (key).

MATERIAL EXAMINED. — Guam. 13°27’N, 144°47’E, Hospital Point, under rocks at landward edge of erosion beach, intertidal, 15. V.1984, coll. R. K. Kropp, 1 5.1 × 4.5 mm (compound ascidian cap) ( GUM 124) ( ZRC 2000.2115). — Asan Point, south of Camel Rock, under stones, intertidal, 16. V.1984, coll. R. K. Kropp, 1 5.5 × 5.2 mm (sponge cap) ( GUM 125B) ( ZRC 2000.2116). — Pago Bay, Taogam Point, from edge of erosion beach, intertidal, 5.IX.1984, coll. R. K. Kropp, 1 (ovig.) 7.7 × 6.4 mm (carrying a thin piece of seaweed) ( GUM 156B) ( ZRC 2000.2117). — Reef flat north of Tanguisson Point, intertidal, 11.III.1992, coll. G. Paulay, 1 7.5 × 6.1 mm (sponge cap) ( GUM 274) ( ZRC 2000.2118).

Philippine Islands. MUSORSTOM 2, Cebu Marine Station, intertidal, 9.XII.1980, 1 4.8 × 4.6 mm ( MNHN unregistered).

Madagascar. Eastern coast, coll. R. Plante, 1 (ovig.) 10.4 × 10.2 mm ( MNHN-B 6878). — SW coast, Tuléar, no depth, no date, 1 (ovig.) 13.5 × 12.9 mm ( MNHN-B 6931). — Nosy-Be, intertidal, II.1962, coll. A. Crosnier, 1 (ovig.) 8.0 × 7.7 mm (sponge cap) ( MNHN-B 6880). — Fort Dauphin, no depth, 1932, 1 13.7 × 13.2 mm (sponge cap) ( MNHN unregistered).

SIZE. — Maximum male size is 13.7 × 13.2 mm, and for females 13.5 × 12.9 mm. Clutch size ranges from around 100 eggs for a female 8.0 × 7.7mm, to about 900 eggs for a female 13.5 × 12.0 mm. Average egg diameter= 0.75 mm. This indicates that C. pentagonalis has planktonic larvae.

DEPTH AND HABITAT. — Lewinsohn (1984) found many specimens in crevices, and under stones in intertidal pools. Most of the specimens examined herein came from the intertidal. The deepest record for C. pentagonalis is 70 m ( Rathbun 1911).

DISTRIBUTION. — Previously known only from the Indian Ocean, now known from the Philippines, and Guam.

DESCRIPTION

Carapace pentagonal in shape, wider than long, moderately convex, covered by a long tomentum especially along carapace margins and walking legs. Branchial groove and cardiac border distinct. Rostrum tridentate, teeth prominent, narrow and sub-acute. Median tooth as long as lateral teeth, deflexed, and on a lower level. Supraorbital margin interrupted by small tooth, followed by deeply concave margin preceding a larger postorbital tooth. Infraorbital margin bears a distinct tooth with another at its base. Subhepatic tubercle present scarcely visible dorsally. Infraorbital tooth, tooth at its base and subhepatic tooth arranged as an oblique row. Anterolateral carapace margin convex, sharply angled like a shoulder and bearing one small tooth slightly below margin at widest point. Area beneath the shoulder slightly excavated. Small posterolateral tooth behind branchial groove. Posterolateral margins convergent, posterior margin slightly convex.

Chelipeds well-developed, carpus bears two strong distal tubercles, propodus smooth. Dactyl strongly curved, fingers gaping.

P2 and p3 shorter than chelipeds, without tubercles, dactyli well-developed, inner margins bearing four or five spines.

P4 and p5 reduced, p4 shortest, p5 sub-dorsal. Dactyli large, strongly curved, opposed by short propodal spines.

Abdomen densely fringed with setae. Uropods well-developed and visible externally. Female sternal sutures 7/8 end apart between bases of p3.

DISCUSSION

Several early authors suggested that C. pentagonalis and C. canaliculata were synonymous, but Lewinsohn (1979) lists the main differences and clearly shows that C. pentagonalis is a valid species.

C. pentagonalis normally carries pieces of camouflage material manufactured from sponges or compound ascidians. However, the female specimen from GUM 156B was carrying a thin, oblong piece of seaweed. Close examination shows that the sheet of seaweed has been cut around all the edges, presumably by the crab. Some sections of the edge are regenerating and the upper surface is approximately half covered with encrusting bryozoans. This suggests that the crab had carried its camouflage for sometime. The crab held the camouflage by inserting the dactyli of p4 and p5 into the under-surface of the seaweed. The cover ratio of the area of the seaweed to cw × cl was 2.5 indicating that it covered the crab was more than adequately.