A new deep-sea genus of the family Polyceridae (Nudibranchia) possesses a gill cavity, with implications for the cryptobranch condition and a 'Periodic Table' approach to taxonomy

Abstract

A new genus and species of a deep-sea dorid nudibranch is described. Elfdaliana profundimontana n. gen, n. sp. is the first taxon of the family Polyceridae with a gill cavity. The new genus possesses diagnostic characters of other polycerids, including globular structures on the branched lateral processes, a radula with broad rachis and differentiated outer lateral teeth. This discovery agrees with recently proposed phylogenetic frameworks and supports a development-based model for the evolution of the dorid nudibranchs, placing the cryptobranch condition as ancestral. A synopsis of the ontogenetic stages representing major dorid cryptobranch and phanerobranch lineages (including novel data on three species) is presented for the first time. Phylotypic periods for the dorid nudibranchs are indicated. It is suggested that the phenomenon of conserved phylotypic periods makes it possible to apply a Periodic Table-like approach to biological taxonomy and phylogenetics.