PHYLOGENY AND RELATIONSHIPS OF PLEUROTOMARIID GASTROPODS (MOLLUSCA, GASTROPODA) - AN ASSESSMENT BASED ON PARTIAL 18S RDNA AND CYTOCHROME-C-OXIDASE-I SEQUENCES

The phylogenetic position of the ancient family Pleurotomariidae withi n the Molluscan class Gastropoda, as well as the relationships of its Recent genera and species, were assessed using an iterative, two-gene (18S rDNA and cytochrome c oxidase I) approach to phylogeny reconstruc tion. In order to orient the Pleurotomariidae within Gastropoda, parti al 18S rDNA sequences were determined for 7 pleurotomariid and 22 othe r gastropods that span the major groups within the class as well as fo r one cephalopod and two polyplacophorans, which serve as outgroups. C ladistic analyses of a sequence of approximately 450 base pairs (bp) n ear the 5' end of the 18S rDNA support the monophyly of the following higher gastropod taxa: Patellogastropoda, Vetigastropoda, Neritopsina, Apogastropoda, and its subclades Caenogastropoda and Heterobranchia. The 18S rDNA sequences and 579 bp of cytochrome c oxidase I (COI) anal yzed separately and together, indicate that Pleurotomariidae are inclu ded within Vetigastropoda but comprise a clade that is the sister grou p to the other families referred to this order. Monophyly of the Pleur otomariidae is also supported by the unique presence of seven separate inserts (ranging in length from 1 to 68 bp) within the V2 variable re gion of the 18S RNA. Relationships of the genera and species within Pl eurotomariidae are fully resolved using ''total molecular evidence'' c onsisting of partial sequences of 18S rDNA and COI and including data on length variation within the inserts.