Journal of the Marine Biological Association of the UK

Research Article

Phylogenetics of Trachylina (Cnidaria: Hydrozoa) with new insights on the evolution of some problematical taxa

Allen G. Collinsa1 c1, Bastian Bentlagea2, Alberto Lindnera3, Dhugal Lindsaya4, Steven H.D. Haddocka5, Gerhard Jarmsa6, Jon L. Norenburga7, Thomas Jankowskia8 and Paulyn Cartwrighta2

a1 NMFS, National Systematics Laboratory, National Museum of Natural History, MRC-153, Smithsonian Institution, PO Box 37012, Washington, DC 20013-7012, USA

a2 Department of Ecology and Evolutionary Biology, University of Kansas, 1200 Sunnyside Avenue, Lawrence, KS 66045, USA

a3 Centro de Biologia Marinha—USP–Rodovia Manoel Hipólito do Rego, Km 131, 5—São Sebastião, SP, Brazil

a4 Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan

a5 Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039, USA

a6 Biozentrum Grindel und Zoologisches Museum, Universität Hamburg, Martin-Luther-King Platz 3, 20146 Hamburg, Germany

a7 Smithsonian Institution, PO Box 37012, Invertebrate Zoology, NMNH, W-216, MRC163, Washington, DC 20013-7012, USA

a8 Federal Institute of Aquatic Science and Technology, Dübendorf 8600, Switzerland

Abstract

Some of the most interesting and enigmatic cnidarians are classified within the hydrozoan subclass Trachylina. Despite being relatively depauperate in species richness, the clade contains four taxa typically accorded ordinal status: Actinulida, Limnomedusae, Narcomedusae and Trachymedusae. We bring molecular data (mitochondrial 16S and nuclear small and large subunit ribosomal genes) to bear on the question of phylogenetic relationships within Trachylina. Surprisingly, we find that a diminutive polyp form, Microhydrula limopsicola (classified within Limnomedusae) is actually a previously unknown life stage of a species of Stauromedusae. Our data confirm that the interstitial form Halammohydra sp. (Actinulida) is derived from holopelagic direct developing ancestors, likely within the trachymedusan family Rhopalonematidae. Trachymedusae is shown to be diphyletic, suggesting that the polyp stage has been lost independently at least two times within trachyline evolution. Narcomedusae is supported as a monophyletic group likely also arising from trachymedusan ancestors. Finally, some data, albeit limited, suggest that some trachyline species names refer to cryptic species that have yet to be sorted taxonomically.

(Received November 29 2007)

(Accepted February 08 2008)

(Online publication September 08 2008)

Correspondence:

c1 Correspondence should be addressed to: Allen G. Collins, NMFS, National Systematics Laboratory, National Museum of Natural History, MRC-153, Smithsonian Institution, PO Box 37012, Washington, DC 20013-7012, USA email: CollinsA@SI.edu