Four hermit crabs of the genus Ciliopagurus are recognized as a complex of species named the “strigatus complex”. They are found in the low intertidal or shallow waters of the Indo-West Pacific. Ciliopagurus strigatus (Herbst, 1804) is characterized by striped legs and chelae with alternate yellow and red transverse colour bands. It is commonly found on reef habitats and is reported from the Red Sea to French Polynesia. Ciliopagurus tricolor Forest, 1995 is reported with certainty from East Africa to Réunion Island, C. vakovako Poupin, 2001 is endemic to the Marquesas Islands, and C. galzini n. sp. is described as a new species from specimens collected in the Tuamotus. Within the 17 extant species of the genus Ciliopagurus, these four species are distinct by the aspect of the ocular acicle with 3-5 terminal spines instead of usually 1 or 2 in the other species, a few morphometric characters, and by their vertical distribution, from intertidal to about 20 m, whereas all the other species are usually collected deeper. The species of the “strigatus complex” are morphologically very similar and can be separated with confidence only by their coloration. All of them have similar colour patterns of transverse bands on the chelipeds and walking legs, but each species can be easily recognized by the distinct colour and/or disposition of these bands. The appraisal of these colour differences as valuable specific indicators is confirmed by phylogenetic analysis of mitochondrial and nuclear DNA sequences.
Crustacea, Decapoda, Diogenidae, Ciliopagurus, sibling species, species-complex, Indo-West Pacific, new species.