Cancer francisci Curtiss, 1938

Ng, Peter K. L., Eldredge, Lucius G. & Evenhuis, Neal L., 2011, The names of decapod and stomatopod Crustacea from Tahiti, French Polynesia, established by Anthony Curtiss in 1938 and 1944, Zootaxa 3099, pp. 43-56 : 51

Cancer francisci Curtiss, 1938 [óhiti]

Cancer ceratophthalmus Pallas, 1772: 83 .

Cancer francisci Curtiss, 1938: 175 , n. syn.

On the basis of the descriptions, Cancer francisci and C. roberti (see below) are without doubt two species of Ocypode (Ocypodidae) . However, their identities are not so easy to ascertain. Joseph Poupin commented (personal communication) that there are only two species of Ocypode common on Tahiti, O. ceratophthalmus ( Pallas, 1772) and O. cordimanus Latreille, 1818 (see also Poupin & Juncker 2010). The other species known from French Polynesia, O. pallidula Jacquinot in Hombron & Jacquinot, 1846, is not known from Tahiti, being present thus far only in the islands of Gambier, Austral, and Tuamotu (see also Poupin 1994, 1996; Poupin & Juncker 2010). However, a careful reading of the observations made by Curtiss allows us to make a reasonable determination.

The species named as Cancer francisci was described as follows: “The purplish sand-crab, called by the Indians óhiti, is found along the sea-side of Tahiti; running swiftly and burrowing in the sand. It is five-eighths of an inch long, and five-eighths of an inch wide. Compared with the Tahiti rock-crabs, its body, considering its length and breadth, is relatively deeper and thicker. The shell between the eyes is folded down in a band, narrower than that of the Tahiti rock-crabs. Behind each eye, on the side of the upper shell, is a single spine, with no tooth behind it. There are hairs on the four hinder pairs of legs, but they are short and not very noticeable. The tail, which is kept folded under the thorax, is of somewhat oblong shape. The body on its upper side is purplish, inclining to dull black, with a few whitish spots; the under side is whitish, with a bluish tinge. The tips of the pincers are whitish. The hindmost pair of legs are not flattened at the end, but sharp-pointed. I saw another very small one, a quarter of an inch long, but, except for size, exactly like the large one. “This creature is very common at Tahiti” ( Curtiss 1938: 174). The second species, named Cancer roberti , was described as follows: “The reddish sand-crab, which shares with the last the name of óhiti, is found, like it, along the seaside, burrowing in the sand. It much resembles the other kind, and has a thick, squarish body, an inch and three-sixteenths long and an inch and three-sixteenths wide. It has the shell folded down in a narrow band between the eyes. There is a single spine behind each eye, on the side of the shell, with no tooth behind it. The hindmost pair of legs are not flattened, but pointed, at their tips. The pincer-legs have the joints nearest the body crested with teeth on the upper side. The four hinder pairs of legs have some short yellowish hairs on them. The body is reddish above, whitish beneath. The eyes are black. The pincers are whitish at their tips. The tail is oblong. This creature scurries speedily about. It is quarrelsome and cannibal, tearing other crabs up and eating them” ( Curtiss 1938: 175).

The specimen of Cancer francisci described was only “five-eighths of an inch wide” (ca. 1.6 cm) and at this size, both O. ceratophthalma and O. cordimanus would be juveniles. In the case of O. ceratophthalmus , juveniles are rather variable in colour, ranging from dark grey to brown or white on the dorsal surface, and/or with mottled patterns and the ventral surfaces white (versus the diagnostic white dorsal carapace surface with a horseshoeshaped black marking and a dark brown to black thoracic sternum of adults), and the eye is ovate and dark grey (versus possessing distinctive projections or “horns” on the tip of the dark grey to black eyes of adults). Cancer roberti is “an inch and three-sixteenths wide” (ca. 3.0 cm), which would correspond with the adult size of O. ceratophthalmus and O. cordimanus . However, at this size, the colour was described as “reddish” and there was no mention of the “horns” on the eyes. Cancer roberti is therefore unlikely to be O. ceratophthalmus . The colour, however, does agree with that of O. cordimanus , with smaller adults tending to be more pale reddish to pinkish, with larger individuals (ca. 4.0 cm in carapace width) being dark grey to light purple and white; and the eyes always deep black.

What was also specifically described for C. roberti was that the “pincer-legs have the joints nearest the body crested with teeth on the upper side” (probably the spiniform crest on the merus) and “four hinder pairs of legs have some short yellowish hairs on them”. Curtiss did not describe the condition of the merus of the cheliped in C. francisci , but this would have been hard to see on juvenile specimens; although the inner margin of the merus in O. cordimanus is generally large and more distinctly lobiform compared to similar sized specimens of O. ceratophthalmus . With regard to the setation of the legs of C. francisci, Curtiss commented that there “are hairs on the four hinder pairs of legs, but they are short and not very noticeable”. The description of the setal pattern on the legs of C. francisci agrees well with that of O. ceratophthalmus . In O. cordimanus , the setae on the legs are usually relatively longer and more noticeable.

On the basis of these observations, it seems reasonable to identify Cancer francisci with O. ceratophthalmus ( Pallas, 1772) , an intertidal species common across the Indo-West Pacific (see Türkay et al. 1996; Davie, 2002). Cancer roberti can be referred to O. cordimanus Latreille, 1818 , a species common on the supralittoral of sandy beaches of the Indo-West Pacific (see Türkay et al. 1996; Huang et al. 1998).