Revisiting Tylaspis anomala Henderson, 1885 (Parapaguridae), with comments on its relationships and evolution

The parapagurid hermit crab Tylaspis anomala Henderson, 1885, has been discovered living in association with anemones in New Caledonia. Very few specimens were known of this species, previously thought to carry its abdomen unprotected, or perhaps bury it in the soft bottom sediment. The study of all available specimens of this striking hermit crab revealed lack of details and morphological inaccuracies in published accounts. As a result, the monotypic genus Tylaspis Henderson, 1885 has been rediagnosed, and T. anomala Henderson, 1885 redescribed and illustrated. The genus Tylaspis has been found to be more closely related to another monotypic genus, Probeebei Boone, 1926, represented by P. mirabilis Boone, 1926, than to any other parapagurid genus. A summary of the taxonomy and diagnosis of P. mirabilis is presented. The morphological similarities and differences, pleopod development, and habitat of these two species are discussed. Possible evolutionary explanations of their unusual morphology are explored.