Revision of the Parasesarma guttatum species complex reveals a new pseudocryptic species in south-east African mangroves

Abstract

Parasesarma De Man, 1895 is the most speciose genus among the family Sesarmidae (Decapoda; Brachyura: Thoracotremata). In the Western Indian Ocean, the genus Parasesarma is represented by five species, although some genetic evidences suggest that P. guttatum could be a species complex including two cryptic species. A new species, Parasesarma capensis, sp. nov., is described, hence splitting P. guttatum into two pseudo-cryptic species. P. capensis, sp. nov. ecologically vicariates P. guttatum southward the Mozambique Channel. While mitochondrial DNA variation and morphological differences well distinguished the two species, genetic nuclear variation is null. This may reflect a short history of reproductive isolation. The distinguishing morphological characters of the new species are the 13-15 rounded tubercles on the movable finger; the upper surface of palm with three transverse crests, one regularly tuberculate and two pectinated, and the shape of the first gonopod. Phylogenetic inference analyses show a sister-species relationship between P. guttatum and P. capensis, sp. nov., and strongly suggest that at least two East African Parasesarma species need a taxonomic revision. The description of this new sesarmid species from south-eastern African coast sheds new light on the overall biogeographic patterns and general biodiversity of this taxon within the Western Indian Ocean.