Great Basin Naturalist


Between May 1992 and April 1996, freshwater sponges (Porifera: Spongillidae) were collected at 24 sites, distributed among 6 sub-major drainage basins in western Montana, to determine the species present. Water samples also were analyzed from 16 of these sites and from 9 sites at which no sponges were detected to characterize sponge habitats chemically. Three species of sponges were identified: Ephydatia muelleri (Em), Eunapius fragilis (Ef), and Spongilla lacustris (Sl). A 4th type of specimen was present at 2 sites but could not be identified because of the absence of gemmules and gemmoscleres. At 46% of the sites containing sponges, more than 1 specimen type was present. Sponges were most commonly found near outlets of lakes, attached to sides or undersides of submerged rocks and logs. They appeared as encrusting (Em, Ef, Sl), lobate (Em), and fingerlike (Sl) growths, varying in color from light tan to green. Dimensions of the spicules varied greatly within each species and expanded previously recorded ranges. No factors limiting sponge distribution were identified, but ranges of conductivity (Em) and of silica (Em, Sl), calcium (Em), and magnesium (Em) concentrations were expanded beyond those reported previously.