Catapagurus tuberculosus (Asakura, 1999)

Osawa, M. & Takeda, M., 2004, Hermit crabs (Crustacea: Decapoda: Anomura: Paguroidea) from submarine caves in the Ryukyu Islands, south-western Japan, Journal of Natural History 38, pp. 1097-1132 : 1112-1113

Catapagurus tuberculosus (Asakura, 1999)

Icelopagurus tuberculosus Asakura, 1999: 382 , figures 1–4.

Catapagurus tuberculosus: Asakura, 2001: 830 , figure 1D, G.

Material examined. NSMT-Cr 14370; one male (SL 5.5 mm); Ie Island ; ‘ Shodokutsu, (=small cave); 26°42.9∞N, 127°50.1∞E; 20 m; 13 October 1990 . NSMT-Cr 14371; one ovigerous female (SL 5.3 mm) and larvae; Ie Island ; ‘ Shodokutsu’; 20 m; 26 May 1993 . NSMT-Cr 14372; one male (SL 5.1 mm), one ovigerous female (SL 5.8 mm); Ie Island ; ‘ Shodokutsu’; 20 m; 27 May 1993 .

Colour. There are no spots, band or stripes on the creamy white ground colour in the preserved specimens examined.

Habitat and behaviour. The type specimens were collected from sandy bottoms, outer side of coral reefs, at depths of 10–20 m (Asakura, 1999).

The specimens examined each carried a small gastropod shell with a large aperture, such as Neritopsis radula (Linnaeus, 1758) , that protected only its abdomen and part of the posterior carapace of the hermit crab. The shell is too small for the hermit crab to retract the thoracic appendages. The field observations by the collectors revealed that this hermit crab took great leaps and moved rapidly on the bottom of the submarine caves when disturbed. The sediments on the floor of the caves are generally very fine except for organic remains including dead shells of bivalves, gastropods and chitons (Hayami and Kase, 1993). The laterally flattened and broad, saber blade-shaped ambulatory dactyli and small shell of C. tuberculosus may indicate an ability to swim, and an adaptive significance for living on soft bottoms.

Distribution. Known only from the Ryukyu Islands (Asakura, 1999; present study), 10– 20 m.

Remarks. Asakura (1999) originally described this hermit crab as a new species of Icelopagurus McLaughlin, 1997 , but he subsequently transferred the species to Catapagurus A. Milne-Edwards, 1880 , in the taxonomic revision of the species of Catapagurus and Hemipagurus Smith, 1881 (Asakura, 2001) . Catapagurus tuberculosus is distinguished from the sole congener, C. sharreri A. Milne-Edwards, 1880 from the north-west Atlantic, by having a row of corneous spines each on the dorsal and ventral margins of the ambulatory dactyli instead of a fringe of dense long setae (Asakura, 2001).

As discussed by Asakura (1999), marked sexual dimorphism of the chelipeds and abdomen are also observed in the specimens examined. Both chelae of females are distinctly more slender and more compressed than those of males. The carpi of the chelipeds are also distinctly more elongate and more slender in females than males. The abdomen of the female is larger than that of the male. In addition to these sexual dimorphic variations, an intraspecific difference in male pleopods was found in two specimens examined. One specimen (NSMT-Cr 14372, SL 5.1 mm) has a uniramous pleopod and an unequally biramous pleopod with very small endopod on the left side of second and third abdominal somites, respectively. Another specimen (NSMT-Cr 14370, SL 5.5 mm) lacks a pleopod on the second somite and has only a uniramous pleopod on the third somite, the number of pleopods agreeing with that of the type material.

Asakura (1999) could not confirm the presence of the fourth left pleopod of females because the abdomen of the female paratype was damaged in the posterior part. Examination of two female specimens (NSMT-Cr 14371, 14372) reveals that they possess a fourth left pleopod that is short and uniramous.

The larvae preserved with an ovigerous female in the same specimen bottle (NSMT-Cr 14371) show a prezoea-like appearance, probably accidentally hatched by fixation. The antennule, antenna and maxillipeds of the larvae are folded, and the marginal setae on these appendages and posterior processes of the telson are covered with delicate cuticles and are not well developed. The very small, rudimentary condition of the third maxilliped, and no trace of pereopods, suggest a normal mode of development in this species.