Naming species with no morphological indicators: species status of Galeolaria caespitosa (Annelida : Serpulidae) inferred from nuclear and mitochondrial gene sequences and morphology Magdalena N. Halt A,E , Elena K. Kupriyanova A,D , Steven J. B. Cooper A,B and Greg W. Rouse C A School of Earth and Environmental Sciences and Australian Centre for Evolutionary Biology and Biodiversity, The University of Adelaide, Adelaide, SA 5005, Australia. B Evolutionary Biology Unit, South Australian Museum, North Terrace, Adelaide, SA 5000, Australia. C Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0202, USA. D Present address: Faculty of Education and Human Sciences, Yokohama National University, Tokiwadai, Hodogaya, Yokohama 240-8501, Japan. E Corresponding author. Email: magdalena.halt@adelaide.edu.au Abstract. Galeolaria caespitosa Lamarck, 1818 is an endemic, gregarious serpulid annelid, ubiquitous along the intertidal zone of southern Australia, occurring from Queensland to Western Australia. We sampled specimens across this range and utilised morphological features and sequences of mitochondrial (cytochrome-b) and nuclear (ITS2) markers to assess the taxonomic status of this morphospecies. No taxonomically significant morphological differences were observed across the range of G. caespitosa. However, the molecular data revealed the existence of the following two well supported clades that were also geographically concordant for the two markers: an eastern clade, consisting of New South Wales and southern Queensland samples, and a south-western group that encompassed samples from the rest of its range. The minimum pairwise distance between members of the two groups was more than 24% for cytochrome-b, with a maximum of 1% within-group variation. In addition, analysis of molecular variation showed a high proportion (97%) of the total variation distributed among the two groups, indicative of long-term isolation of the two clades. These results suggest that G. caespitosa comprises at least two cryptic species. Here, we discuss the merits of naming new Galeolaria species, given there were no consistent morphological differences detectable and the absence of details on the type locality for G. caespitosa. We conclude that a new species of Galeolaria is warranted and describe it here as G. gemineoa. Introduction Molecular phylogenetics has redefined the way we currently classify and describe species. Often where traditional taxonomic methods have found little or no morphological or ecological variation, differences in genetic sequence data have given rise to many new species or species-complex descriptions (Schulze et al. 2000; Patti and Gambi 2001; Jolly et al. 2006). In particular, there are now numerous examples of widespread taxonomic ‘species’ that actually comprise two or more distinct evolutionary lineages with associated geographic structure (Knowlton 1993; Wiens 2004; Waters et al. 2005; York et al. 2008). Better understanding of the composition of species and their distributions can assist in identifying areas of endemism and has important implications for conservation and management (Palumbi 2003; Rubinoff 2006). Wide habitat ranges have been documented for several marine annelid species, particularly those that are free-spawning and have pelagic larval phases (e.g. Westheide and Schmidt 2003; Drake et al. 2007; Meyer et al. 2008). During the time spent in the plankton, larvae can be dispersed by ocean currents, and also commonly via ballast water or fouling communities on marine vessels. Although in some cases, molecular genetic analyses have confirmed the presence of wide-ranging species (e.g. a cirratulid, Ctenodrilus serratus, in the Atlantic; Westheide et al. 2003), other species have been shown to comprise multiple cryptic species with significant genetic differentiation (e.g. an orbiniid, Scoloplos cf. armiger; Bleidorn et al. 2006). Recently, molecular genetic and detailed morphological assessment of three putative Proscoloplos (Orbiniidae, Annelida) species occurring across a wide geographic range identified the existence of only a single species, P. cygnochaetus, with a worldwide distribution (Meyer et al. 2008). These and other studies (e.g. Nygren et al. 2005) have highlighted that many morphological characters that have traditionally been used for polychaete taxonomy may be Ó CSIRO 2009 10.1071/IS09003 1445-5226/09/030205 CSIRO PUBLISHING www.publish.csiro.au/journals/is Invertebrate Systematics, 2009, 23, 205–222