Cryptodromia fallax ( Lamarck, 1818 )

Mclay, Colin L., 2001, Dynomenidae and Dromiidae (Decapoda, Brachyura) from Guam, Philippine Islands, Tonga and Samoa, Zoosystema 23 (4), pp. 807-856 : 832-833

Cryptodromia fallax ( Lamarck, 1818)

Dromia fallax Lamarck, 1818: 264 .

Cryptodromia canaliculata Stimpson, 1858: 240 . — Ihle 1913: 41. — Ward 1941: 1. — Lewinsohn 1977: 18, text fig. 4a-c; 1979: 8, text fig. 2B; 1984: 108.

Cryptodromia fallax – McLay 1993: 206, fig. 18e. — [Not Ng et al. 2000: 159, fig. 1d (= C. tumida Stimpson, 1858 )].

MATERIAL EXAMINED. — Guam. Gun Beach, 13°27’N, 144°47’E, 3-5 m, fore reef, 5.VII.1999, coll. L. Kirkendale, 1 (ovig.) 7.9 × 6.2 mm (sponge cap) ( UGI no registration number) ( ZRC 2000.0751).

Western Indian Ocean. Salomon, Chagos Archipelago, HMS Sealark, 5°20’S, 72°15’E, no depth, 1905, coll. J. Stanley Gardiner, 1 (ovig.) 10.6 × 9.3 mm ( USNM).

SIZE. — Maximum cw for females is 15.0 mm and the smallest ovigerous female had cw= 6.8 mm. Clutch size range is 147- 196 eggs. Mean egg diameter= 0.7 mm. The female from Guam had 144 eggs, diameter 0.68 mm, while the female from Salomon had 250 eggs, diameter 0.7 mm.

DEPTH AND HABITAT. — Low intertidal to around 3 m, on sponges. Crabs normally carry pieces of sponge or compound ascidian camouflage.

DISTRIBUTION. — From Red Sea to Philippine Islands and from West Pacific to French Polynesia. Besides the Philippines, C. fallax ( Lamarck, 1818) , is known from Japan and China and has been reported from the northern Mariana Island of Maug East, as C. canaliculata Stimpson, 1858 , by Takeda et al. 1994.

DISCUSSION

For the full synonymy and description of C. fallax see McLay (1993: 206). McLay (1993) showed that C. canaliculata is a synonym of C. fallax , but the status of Ihle’s (1913) varieties, “ C. canaliculata var. sibogae ” and “ C. canaliculata var. obtusifrons ”, was not discussed. It is unclear whether these two varieties should be regarded as separated species. Ihle described the first variety as follows: Cryptodromia canaliculata var. sibogae Ihle, 1913 is: “A species of small size (mature female 6.5 × 6.0 mm), carapace setose, surface slightly convex, sculptured, gastrocardiac suture distinct. All three rostral teeth acute, similar in length, narrower and sharper than in the typical form (i.e. C. canaliculata ). Supraorbital, postorbital and suborbital teeth well-developed and sharp, orbital fissure absent. A single welldeveloped anterolateral tooth, behind which the carapace margin is convex, representing the rudiment of the second anterolateral tooth, and a small, but clearly visible, posterolateral tooth. There is a well-developed subhepatic tubercle, but the tubercle on the ridge above the pleural suture is absent. The suprasutural ridge bulges, but is not very distinct, which is one reason for regarding this variety as being different from the typical form. In summary, the variety sibogae is different because of the smaller size, narrow rostral teeth and absence of a distinct tooth on the suprasutural ridge” (translated from German). Ihle (1913) notes that it is possible that the specimen of C. canaliculata , mentioned by De Man (1888a: 403), belongs to this variety, because it lacked a suprasutural tubercle.

Comparing his other variety, Cryptodromia canaliculata var. obtusifrons Ihle, 1913 , with the typical form Ihle described it as follows: “The general body shape and shape of the carapace are the same as in the typical form, as is the sculpturing on the carapace surface. The gastrocardiac suture is very deep. The lateral rostral teeth are more slender, as in the typical form, but the median rostral tooth appears different. This tooth is short, deflexed and ends bluntly (hence the varietal name) so that, in dorsal view, the tooth is only partially visible and the lateral teeth are much longer, projecting further forward than the median tooth. The form of the supra-, infra- and extraorbital (i.e. postorbital corner) teeth, the presence of a subhepatic tubercle, the presence of a groove beside the orbit, the absence of an orbital fissure are all in agreement with the typical form. In contrast to the typical form, the tubercle on the suprasutural ridge is absent in both varieties. In the variety obtusifrons , only one well-developed anterolateral tooth is present, behind which there us only a rudiment of the second tooth. The pereopods of this variety are not different” (translated from German). With only one specimen, a small male cl= 7.5 mm, Ihle believed that its systematic position was uncertain, but did not warrant recognition as a different species.

Subsequently, no other authors have referred specimens to these varieties. The main difference between the two varieties is in the shape and size of the rostral and orbital teeth. Ihle (1913) indicated that further specimens are necessary to clearly determine the status of these varieties and this remains true today. Only two specimens were available for the present study and these do not help to resolve this problem. However, it is worth noting that differences in the apparent relative size of the rostral teeth, very much depend upon whether the specimen is viewed exactly horizontal or not. Tilted forward, the median tooth can appear shorter than the lateral teeth, and vice versa. Variation in the shape of the rostral and orbital teeth certainly occur within species and thus it may well be that Ihle’s varieties represent no more than intraspecific variations.