Genetic analysis of bamboo corals (Cnidaria: Octocorallia: Isididae): does lack of colony branching distinguish Lepidisis from Keratoisis?

Bamboo corals (family Isididae) are among the most easily recognized deep-water octocorals due to their articulated skeleton comprised of non-sclerite calcareous internodes alternating with proteinaceous nodes. Most commonly encountered in the deep-sea are species in the subfamily keratoisidinae, including the genera Acanella Gray, 1870, Isidella Gray, 1857, Keratoisis Wright, 1869, and Lepidisis Verrill, 1883. Systematists have debated whether Lepidisis and Keratoisis should be defined on the basis of "colony branching." Although recent taxonomic keys use "colonies unbranched" to distinguish Lepidisis, the original description of the genus included both branched and unbranched morphologies, with both forms also classified in Keratoisis. This study analyzed mitochondrial DNA sequence variation from isidids collected between 500–2250 m depth to address the following question: are unbranched, whip-like bamboo corals in the subfamily keratoisidinae monophyletic? DNA sequences of the msh1 gene (1426 nucleotides) from 32 isidids were used to construct a phylogeny. Coding of gaps provided additional informative characters for taxon discrimination. The results show five well-supported clades, all grouping both branched and unbranched colony morphologies; there was no single mono-phyletic clade of unbranched Keratoisidinae. The msh1 phylogeny suggests that the distinction between the genera Lepidisis and Keratoisis should not be based on whether or not colonies branch.