Phylogeny of Halgerda (Mollusca : Gastropoda) based on combined analysis of mitochondrial CO1 and morphology

Abstract

A phylogeny of the nudibranch Halgerda Bergh, 1880 is presented based on mitochondrial CO1 and compared with a previously published morphology-based phylogeny. Incongruence length difference (ILD) tests indicated possibly conflicting phylogenetic signals. Both separate and combined analyses resulted in trees that were very similar in topology, both to each other and to the morphology-based tree (albeit with lower consistency and retention indices). Some differences are noted in the topology based on the optimality criteria used: parsimony and maximum likelihood. Results of this study indicate that the CO1 gene contains sufficient phylogenetic signal for inferring species-level phylogeny in the Nudibranchia and also supports many of the clades in the morphological phylogeny. Specifically, the more basal clades of the morphology-based phylogeny are supported with differences noted at the most terminal taxa.