Phylogenomics, life history and morphological evolution of ophiocomid brittlestars

International audienceBrittlestars in the family Ophiocomidae are large and colourful inhabitants of tropical shallow water habitatsacross the globe. Here we use targeted capture and next-generation sequencing to generate robust phylogenomictrees for 39 of the 43 species in order to test the monophyly of existing genera. The large genus Ophiocoma, ascurrently constituted, is paraphyletic on our trees and required revision. Four genera are recognised herein: anexpanded Ophiomastix (now including Ophiocoma wendtii, O. occidentalis, O. endeani, O. macroplaca, andOphiarthrum spp), Ophiocomella (now including the non-fissiparous Ophiocoma pumila, aethiops and valenciae) andBreviturma (now including Ophiocoma pica, O. pusilla, O. paucigranulata and O. longispina) and a restrictedOphiocoma. The resulting junior homonym Ophiomastix elegans is renamed O. brocki. The genus Ophiomastixexhibits relatively high rates of morphological disparity compared to other lineages. Ophiomastix flaccida and O.(formerly Ophiarthrum) pictum have divergent mitochondrial genomes, characterised by gene-order rearrange-ments, strand recoding, enriched GT base composition, and a corresponding divergence of nuclear mitochondrialprotein genes. The new phylogeny indicates that larval and developmental transitions occurred rarely. Larvalculture trials show that species with abbreviated lecithotrophic larval development occur only withinOphiomastix, although the possible monophyly of these species is obscured by the rapid early radiation withinthis genus. Asexual reproduction by fission is limited to one species-complex within Ophiocomella, also char-acterised by elevated levels of allelic heterozygosity, and which has achieved a relatively rapid global dis-tribution. The crown ages of the new genera considerably predate the closure of the Tethyan seaway and all fourare distributed in both the Atlantic and Indo-Pacific Oceans. Two species pairs appear to reflect the closure of thePanama Seaway, although their fossil-calibrated node ages (12–14 ± 6 my), derived from both concatenatedsequence and multispecies coalescent analyses, considerably predate the terminal closure event. Ophiocomaerinaceus has crossed the East Pacific barrier and is recorded from Clipperton Island, SW of Mexico