ARE MEIOFAUNAL SPECIES COSMOPOLITAN - MORPHOLOGICAL AND MOLECULAR ANALYSIS OF XENOTRICHULA-INTERMEDIA (GASTROTRICHA, CHAETONOTIDA)

Many meiofaunal species are reported to be cosmopolitan, but due to un certainties of identification, the affiliation of specimens from geogr aphically distant areas to the same species-taxon is problematic. In t his study, we examined morphological and molecular variation in sample s of Xenotrichula intermedia Remane (Gastrotricha: Chaetonotida) from the Mediterranean Sea, the northwestern Atlantic and the northern Gulf of Mexico. Univariate analysis of 16 morphological traits was unable to detect differences among populations, except for the length of the pharynx, which was significantly shorter in the Gulf of Mexico specime ns. Canonical discriminant analysis separated the Gulf of Mexico speci mens from the other two populations, with pharynx length contributing about half of the total discrimination. Molecular analysis based on re striction-fragment length polymorphisms (RFLPs) in a 710-base pair pol ymerase chain-reaction (PCR) product representing roughly half of the mitochondrial cytochrome oxidase I (COI) gene detected four haplotypes : one each from the Mediterranean and the Gulf of Mexico populations a nd two coexisting within the Atlantic population. The estimated nucleo tide-sequence divergence calculated for each pairwise combination of h aplotypes (based on the proportion of shared fragments) ranged from 5. 3 to 11.5%. The high genetic divergence and the inability to clearly s eparate populations based on morphology suggest that individuals chara cterized by different haplotypes are genetically isolated sibling spec ies.