Marine Biology (1996) 125:569-578 9 Springer-Verlag 1996 D. W. Foltz 9W. B. Stickle 9E. L. Campagnaro 9A. E. Himel Mitochondrial DNA polymorphisms reveal additional genetic heterogeneity within the [eptasteria$ hexacti$ (Echinodermata: Asteroidea) species complex Received: 19 October 1995/Accepted: 25 November 1995 Abstract Sea stars of the Leptasterias hexaais complex are important members of the rocky intertidal com- munity of the temperate and subarctic North American Pacific coasts. Recent attempts to determine the genetic structure and taxonomic relationships of these sea stars have not been completely successful, due to the combi- nation of extreme morphological variability and rela- tive scarcity of taxonomically-informative genetic (allozyme) polymorphisms. The present study used mitochondrial DNA restriction-site polymorphisms for PCR (polymerase chain-reaction)-amplified products to provide additional information about this complex. Five restriction-site haplotypes were identified in southern Alaska and in the Puget Sound region that were allozymically distinct. Because the allozymic dif- ferences (Nei's unbiased genetic differences > 0.08) are maintained in sympatry, the haplotypes behave evolu- tionarily as conventional species. Although most haplotypes show deficiencies of heterozygotes for poly- morphic allozyme loci, there is no evidence for the existence of cryptic species within any of the haplo- types. Rather than consisting of a few polytypic and cosmopolitan species, the L. hexactis complex is appar- ently composed of numerous species with more restricted ranges. Determining the exact ranges and taxonomic relationships of the various species will re- quire additional study. Introduction The Leptasterias hexactis species complex consists of small, six-rayed, morphologically-variable sea stars Communicated by N.H. Marcus, Tallahassee D.W. Foltz (IE) 9 W.B. Stickle- E.L. Campagnaro. A.E. Himel Department of Zoology and Physiology, Louisiana State University, Baton Rouge, Louisiana 70803-1725, USA that are commonly found in the rocky intertidal zone of the North American Pacific coast from southern Cali- fornia to the Aleutian Islands. Despite the large num- ber of ecological and physiological studies of these sea stars, the taxonomic status of this species complex remains unresolved. The most recent monographic re- vision of the genus (Fisher 1930) recognized three spe- cies (L. aequalis, L. hexactis and L. pusilla) within the complex, with several forms and subspecies of uncer- tain genetic status within L. aequalis and L. hexactis. Currently, four intertidal Leptasterias species are rec- ognized in some taxonomic keys for the North Ameri- can Pacific coast (Smith and Carlton 1975; Kessler 1985; Ricketts et al. 1985): L. epichlora (Brandt, 1835), L. aequalis (Stimpson, 1862), L. hexactis (Stimpson, 1862) and L. pusilla Fisher, 1930. Other recent taxo- nomic keys and field guides for the North American Pacific coast (Snively 1978; Lambert 1981; Kozloff 1987) accepted Chia's (1964, 1966) synonymizing of L. epichlora, L. aequalis and L. hexactis into a single (presumably polymorphic) species. Following Fisher (1930), who rejected the name L. epichIora because Brandt's (1835) original description was based or~ a five-rayed specimen, Chia (1966) used the name L. hexactis to refer to all intertidal Leptasterias spp. in the Puget Sound region of Washington. Recent analyses of allozyme variation in intertidal Leptasterias populations (Kwast et al. 1990 - hereafter cited as KFS for brevity; Stickle et al. 1992; Foltz and Stickle 1994) reported genetic structures within collec- tions that were incompatible with the presence of a single panmictic species. KFS segregated L. epichlora and L. hexactis as genetically-distinct species that were sympatric in both the Lynn Canal region of south- eastern Alaska and around San Juan Island in Puget Sound, Washington, USA. Individuals morphologi- cally intermediate between L. epichlora and L. hexactis were common in Washington but absent from Alaska. These morphologically intermediate sea stars (which were also genetically intermediate between the two