Abstract
The San Marcos River in Central Texas has been well studied and has been demonstrated to be remarkably specious. Prior to the present study, research on free-living invertebrates in the San Marcos River only dealt with hard bodied taxa with the exception of the report of one gastrotrich, and one subterranean platyhelminth that only incidentally occurs in the head spring outflows. The remainder of the soft-bodied metazoan fauna that inhabit the San Marcos River had never been studied. Our study surveyed the annelid fauna and some other soft-bodied invertebrates of the San Marcos River headsprings. At least four species of Hirudinida, two species of Aphanoneura, one species of Branchiobdellida, and 11 (possibly 13) species of oligochaetous clitellates were collected. Other vermiform taxa collected included at least three species of Turbellaria and one species of Nemertea. We provide the results of the first survey of the aquatic annelid fauna of the San Marcos Springs, along with a dichotomous key to these annelids that includes photos of some representative specimens, and line drawings to elucidate potentially confusing diagnostic structures.
Highlights
The San Marcos River in Hays County, Texas (29°53.505'N; 97°55.973'W) is a spring fed river supplied with physicochemically stable water from the Edwards Aquifer (Crow 2012; Musgrove and Crow 2012)
Despite its low taxonomic resolution, findings from this study suggested a remarkable amount of diversity, with twelve separate orders reported from the gut contents of this one species of fish
At least 4 species of epigean Hirudinida, 2 species of Aphanoneura, 1 species of Branchiobdellida, and 11 species of oligochaetous clitellates are present in the San Marcos River (SMR) and identified
Summary
The San Marcos River in Hays County, Texas (29°53.505'N; 97°55.973'W) is a spring fed river supplied with physicochemically stable water from the Edwards Aquifer (Crow 2012; Musgrove and Crow 2012). Spring Lake and the upper 2 or 3 km of the spring run supports a rich biotic community (Edwards and Arnold 1961, Bowles et al 2007, Gibson et al 2008). The Comal Springs riffle beetle (Heterelmis comalensis Bosse, Tuff, and Brown) is the only protected invertebrate species that occurs in the San Marcos River (SMR). Many of the endemic invertebrates of Spring Lake and the San Marcos Springs are generally considered marine relicts (Holsinger and Longley 1980, Hershler and Longley 1986, Gibson et al 2008). Endemism is high for some of the invertebrate taxa; especially taxa that are poor dispersers and have long inhabited the SMR
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