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 in the family Sesarmidae (Decapoda: Brachyura: Thoracotremata). In the western Indian Ocean, Parasesarma is represented by five species only, although some genetic evidence suggests that P. guttatum could be a species complex comprising two cryptic species. Accordingly, P. guttatum is here split into two pseudocryptic species, and a new species, Parasesarma capensis, sp. nov., is described. P. capensis, sp. nov. fills the same ecological niche as P. guttatum south of the Mozambique Channel. While variation in mitochondrial DNA and morphological differences clearly distinguish the two species, there is no nuclear genetic variation. 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 the 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 the south-eastern African coast sheds new light on the overall biogeographic patterns and general biodiversity of this taxon within the western Indian Ocean.