Pagurixus nomurai Komai and Asakura, 1995

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 : 1109-1110

Pagurixus nomurai Komai and Asakura, 1995

Pagurixus nomurai Komai and Asakura, 1995: 341 , figures 1–3; Nomura et al., 1996: 14 (list);

Hoover, 1998: 261, unnumbered figure; Kato and Okuno, 2001: 85, 146, unnumbered figures.

Material examined. NSMT-Cr 14361: one male (SL 5.2 mm); Ie Island ; ‘ Shodokutsu’ (=small cave); 26°42.9∞N, 127°50.1∞E; 20 m; 2 July 1990 . NSMT-Cr 14362; one male (SL 4.0 mm); Ie Island ; small tunnel near ‘ Shodokutsu’; 20 m; 13 October 1990 . NSMT-Cr 14363; one male (SL 4.4 mm); Shimoji islet, Miyako Group; ‘ Devil’s Palace’; 24°49.6∞N, 125°08.2∞E; 25 m; 10 June 1991 . NSMT-Cr 14364; one ovigerous female (SL 2.8 mm); Shimoji islet, Miyako Group; ‘ Goonies’, part of ‘ Devil’s Palace’; 24°49.6∞N, 125°08.2∞E; 25 m; 18 November 1995 . NSMT-Cr 14380; two males (SL 1.4, 1.8 mm), one female (SL 3.0 mm); Shimoji islet, Miyako Group; ‘Goonies’, part of ‘Devil’s Palace’; 25 m; 31 July 1999. NSMT-Cr 14381; two males (SL 1.0, 1.2 mm), one female (SL 1.5 mm); Shimoji islet, Miyako Group; ‘ Coral Hole’; 24°48.0∞N, 125°09.0∞E; 24–25 m; 31 July 1999 . NSMT-Cr 14382; one male (SL 1.0 mm); Irabu islet, Miyako Group; ‘ Twin Hole’; 24°51.6∞N, 125°10.0∞E; 14–15 m; 1 August 1999 . NSMT-Cr 14383; two males (SL 0.8, 1.1 mm); Irabu islet, Miyako Group; ‘ Cross Hole’; 24°51.6∞N, 125°09.5∞E; 20–25 m; 3 August 1999 . NSMT-Cr 14384; one female (SL 1.7 mm); Shimoji islet, Miyako Group; ‘W-arch’; 24°51.7∞N, 125°09.7∞E; 14–15 m; 3 August 1999 . NSMT-Cr 14385; two males (SL 1.0, 1.4 mm); Shimoji islet, Miyako Group; ‘ Black Hole’; 24°49.1∞N, 125°08.3∞E; 35 m; 31 July 1999 .

Colour. See Komai and Asakura (1995), Hoover (1998) and Kato and Okuno (2001).

Habitat and behaviour. Pagurixus nomurai is one of the common hermit crabs found between branches or plates of dead corals in moats of the Ryukyu Islands.

Field observations showed that this species rapidly moved on to dead corals when frightened, as in some other members of Pagurixus Melin, 1939 . Kato and Okuno (2001) provided a series of photographs showing the interesting behaviour of P. nomurai . This species was reported to abandon its shell and run off using its long ambulatory legs when frightened. Similar behaviour has been reported in fastmoving, active hermit species such as Catapaguroides hooveri McLaughlin and Pittman, 2002 and young Dardanus deformis (H. Milne Edwards, 1836) (McLaughlin and Pittman, 2002) .

Distribution. Ryukyu and Izu Islands (Komai and Asakura, 1995) and Hawaiian Islands (Hoover, 1998); 3– 25 m.

Remarks. Pagurixus nomurai is distinguished from its closest relative, P. maorus (Nobili, 1906) , by the anterior lobe of the sixth thoracic sternite with anterolateral angles strongly produced laterally and the posterior lobes of the telson with much smaller spines on the terminal margin (Komai and Asakura, 1995).

The largest male specimen examined (NSMT-Cr 14361, SL 5.2 mm) is considerably larger than the type material (SL 2.7–4.3 mm) of Komai and Asakura (1995). The right chela is extremely elongate, 3.1 times as long as the maximum breadth (2.3–2.4 times in the type series). Four female specimens (NSMT-Cr 14364, 14380, 14381, 14384; SL 1.5–3.0 mm) are generally similar to the other male specimens examined in the armature of the right cheliped.

As pointed out by Komai and Asakura (1995), the present material also has an intraspecific variation in the armature of the merus of the right second pereopod. The small but distinct spine on the subdistal part of the ventral margin is occasionally reduced to a very small serration or may be absent. An additional variation is observed in gonopores of the females. Three specimens (NSMT-Cr 14364, 14380, 14384; SL 1.7–3.0 mm) have paired gonopores on both the coxae of the third pereopods, whereas one specimen (NSMT-Cr 14381, cl 1.5 mm) possesses only a single gonopore on the left leg. This intraspecific variability is also known in Pagurixus anceps (Forest, 1954) and P. laevimanus (Ortmann, 1892) (McLaughlin and Haig, 1984) .

The small male specimens (NSMT-Cr 14380, 14381, 14382, 14383, 14385; SL 0.8–1.4 mm) lack a tuft of stiff setae covering the gonopore on the coxa of the right fifth pereopod and crossing from right to left. The possession of the tuft is a diagnostic character unique to Pagurixus species (McLaughlin and Haig, 1984). Since the other morphological structures of these specimens generally agree well with the original description of P. nomurai by Komai and Asakura (1995), the lack of a tuft on the coxa of the right fifth pereopod in the male is considered to represent a sexually immature condition.