Diversity and distribution of the Gastropoda Opisthobranchia from the Atlantic Ocean: A global biogeographic approach

A zoogeographic Study of the Opisthobranchia (Mollusca, Gastropoda) from the Atlantic Ocean was carried Out. Data on Opisthobranch Occurrence were collated from literature records and databases. An estimated 1066 species were considered for this Study, which belonged to the orders Cephalaspidea, Anaspidea, Sacoglossa, Notaspidea and Nudi-branchia. Biogeographical patterns were analysed using Cluster analysis (TWINSPAN) and ordination MDS (non-metric multidimensional scaling program). The richness of opisthobranchs increases from polar to tropical regions along Atlantic shores. The cluster analysis showed that there is a latitudinal and longitudinal separation of the biogeographical areas. The amphiatlantic species can be separated into four groups according to their distribution: G1.1.- the geographic range of species is limited to cold water on both sides of the Atlantic; G1.2.- species with geographic ranges limited to the western Arctic and Boreal regions with a wide distribution in the eastern Atlantic, front the eastern Arctic or the eastern Boreal region to the Lusitanian and Mediterranean provinces; G2.1.- species with geographic ranges, limited to the Caribbean and Mauritanian-Senegalese areas; G2.2.- species with a wide geographical distribution along both Atlantic shores.