Molecular evidence for cryptic speciation within the widespread Antarctic crustacean Ceratoserolis trilobitoides (Crustacea, Isopoda)

The controversial taxonomic status of Ceratoserolis trilobitoides (Eights 1833) is re-evaluated with sequences from the mitochondrial 16S ribosomal RNA gene. Within C. trilobitoides sensu Wagele 1986 two sharply distinct groups of haplotypes are present. The pairwise sequence divergence is small within the groups but large between them with no intermediate distances (less than or equal to0.7 vs. greater than or equal to5.8 percent corrected sequence divergence). The large inter-group distance persists also in areas where both types occur in sympatry. The amount of genetic diversity between the haplotypes is in the lower range of genetic distances between undisputed sister species of the same family for this gene. The molecular data therefore strongly suggest that Ceratoserolis trilobitoides sensu lato contains at least one, perhaps more, previously overlooked species. Accounts of C trilobitoides in the literature, especially from the Antarctic Peninsula, should therefore be taken with caution.