When Ontogeny Matters: A New Japanese Species of Brittle Star Illustrates the Importance of Considering both Adult and Juvenile Characters in Taxonomic Practice

PLoS One. 2015 Oct 28;10(10):e0139463. doi: 10.1371/journal.pone.0139463. eCollection 2015.


Current taxonomy offers numerous approaches and methods for species delimitation and description. However, most of them are based on the adult characters and rarely suggest a dynamic representation of developmental transformations of taxonomically important features. Here we show how the underestimation of ontogenetic changes may result in long term lack of recognition of a new species of one of the most common ophiacanthid brittle stars (Echinodermata: Ophiuroidea) from the North Pacific. Based on vast material collected predominantly by various Japanese expeditions in the course of more than 50 years, and thorough study of appropriate type material, we revise the complex of three common species of the ophiuroid genus Ophiacantha which have been persistently confused with each other. The present study thus reveals the previously unrecognized new species Ophiacantha kokusai sp.nov. which is commonly distributed off the Pacific coast of Japan. The new species shows developmental differentiation from the closely related species Ophiacantha rhachophora H. L. Clark, 1911 and retains clearly expressed early juvenile features in the adult morphology. Another species, Ophiacantha clypeata Kyte, 1977, which had been separated from O. rhachophora, is in turn shown to be just a juvenile stage of another North Pacific species, Ophiacantha trachybactra H.L. Clark, 1911. For every species, detailed morphological data from both adult and juvenile specimens based on scanning electron microscopy are presented. A special grinding method showing complex internal features has been utilized for the first time. For all three species in this complex, a clear bathymetric differentiation is revealed: O. rhachophora predominantly inhabits shallow waters, 0-250 m, the new species O. kokusai lives deeper, at 250-600 m, and the third species, O. trachybactra, is found at 500-2,000 m. The present case clearly highlights the importance of considering developmental transformations, not only for a limited number of model organisms, but as part of the taxonomic process.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aging
  • Animals
  • Echinodermata / classification*
  • Echinodermata / physiology*
  • Echinodermata / ultrastructure
  • Species Specificity
  • Temperature

Grant support

This work was supported by Census of Marine Life grant to TOH to map the ophiuroid fauna of the global seafloor and by a grant to TF and AM from the Director General of National Museum of Nature and Science, Japan, by a grant to TF from the Japan Society for the Promotion of Science (Scientific Research [C] No. 25440226) and by a grant through Moscow State University to AM from the Russian Science Foundation (grant 14-50-00029, SEM study and depository of selected ophiuroid specimens for comparative purposes).