Gelasimus Latreille, 1817

Shih, Hsi-Te, Ng, Peter K. L., Davie, Peter J. F., Schubart, Christoph D., Türkay, Michael, Naderloo, Reza, Jones, Diana & Liu, Min-Yun, 2016, Systematics of the family Ocypodidae Rafinesque, 1815 (Crustacea: Brachyura), based on phylogenetic relationships, with a reorganization of subfamily rankings and a review of the taxonomic status of Uca Leach, 1814, sensu lato and its subgenera, Raffles Bulletin of Zoology 64, pp. 139-175 : 151

Gelasimus Latreille, 1817

( Fig. 7 )

Gelasimus Latreille, 1817: 517 . Type species: Cancer vocans Linnaeus, 1758 by subsequent designation, see H. Milne Edwards (1841: pl. 18, fig. 1). Gender masculine.

Latuca Bott, 1973b: 317. Type species: Mesuca (Latuca) neocultrimana Bott, 1973 by original designation. Gender feminine.

Mesuca Bott, 1973b: 316 . Type species: Cancer tetragonon Herbst, 1790 by original designation. Gender feminine.

Thalassuca Crane, 1975: 75. Type species: Cancer tetragonon Herbst, 1790 by original designation. Gender feminine.

Diagnosis. Medium- to large-sized (carapace width about 20–30 mm in adults); dorsal carapace surface without posterolateral striae; front narrow; cornea round; eyestalks slender; adult male chelipeds very large, always right-handed, pollex without ventral carina, outer surface of major manus with moderate to large tubercles; male pleonites free; pleonal locking mechanism absent; setae present on lateral margins of posterior stem region of urocardiac ossicles in gastric mill. Indo-West Pacific.

Species included:

1. Gelasimus borealis ( Crane, 1975)

2. Gelasimus dampieri ( Crane, 1975)

3. Gelasimus hesperiae ( Crane, 1975) (nomen protectum) = Gelasimus tetragonon var. spinicarpa Kossmann, 1877 (nomen oblitum)

4. Gelasimus jocelynae ( Shih, Naruse & Ng, 2010)

5. Gelasimus neocultrimanus (Bott, 1973)

= Uca (Thalassuca) vocans pacificensis Crane, 1975 6. Gelasimus tetragonon ( Herbst, 1790)

= Gelasimus affinis Guérin, 1829

= Gelasimus duperreyi Guérin, 1829

= Gelasimus variatus Hess, 1865

7. Gelasimus vocans ( Linnaeus, 1758)

= Gelasimus marionis Desmarest, 1823

= Gelasimus nitidus Dana, 1851

= Gelasimus cultrimanus White, 1847

= Uca marionis forma excisa Nobili, 1906 8. Gelasimus vomeris ( McNeill, 1920)

Remarks. Gelasimus is widely-distributed in the Indo- West Pacific ( Fig. 4 ). Bott (1973b) established Mesuca as a genus including two subgenera, Mesuca (Mesuca) for Uca tetragonon and four other species now reassigned elsewhere, and Mesuca (Latuca) for U. neocultrimana and three other species also here reassigned to other genera. The current morphological and genetic data suggests this is one monophyletic group. If future studies indicate that Gelasimus is polyphyletic, then Mesuca and Latuca would be available names for use as possible subgenera or genera.

Interestingly, Shih et al. (2010) found that the 16S and COI markers do not show differences between the species within the complex of U. borealis , U. dampieri , U. vocans and U. vomeris , despite good morphological characters to separate them. However, some species can be successfully separated genetically using the nuclear internal transcribed spacers (ITS-1) (Shih unpublished; Chu et al., 2015), which suggests that speciation has been very recent.

While Gelasimus is the only genus with right-handed cheliped for most males, the remaining species are right- or left-handed with nearly the same ratio ( Barnwell, 1982; Yamaguchi, 1994). Juvenile males possess two large chelipeds, and the asymmetry will be attained by losing of either one cheliped that regenerates into a small cheliped ( Morgan, 1923; Yamaguchi & Henmi, 2001). However, the mechanism of losing the left cheliped by juvenile Gelasimus species is still unknown.

Figures

Fig. 7. Photographs of some species of the genus Gelasimus. A, G. borealis (Taiwan); B, G. dampieri (Northern Territory, Australia); C, G. hesperiae (Zanzibar, holotype); D, G. jocelynae (Penghu, Taiwan); E, G. neocultrimana (Fiji); F, G. tetragonon (Penghu, Taiwan); G, G. vocans (Labuan, Malaysia); H, G. vomeris (Queensland, Australia).

Fig. 4. The distribution of 11 genera of fiddler crabs, mainly based on Crane (1975) and the website (http://www.fiddlercrab.info/index. html; Rosenberg, 2014).