ECOLOGICAL OBSERVATIONS OF 2 PLEUROCERID GASTROPODS - ELIMIA-CLARA (LEA) AND E-CAHAWBENSIS (SAY)

The ecology of two pleurocerid gastropods, Elimia (= Goniobasis) clara (Lea) and E. cahawbensis cahawbensis (Say) was studied in Little Schu ltz Creek in Bibb County, Alabama. The study area is part of the Cahab a River drainage basin. Elimia clara was found in greater proportions in riffle areas of the study stream, whereas E. cahawbensis was evenly distributed between riffles and pools. Both species were similar in s ize-at-hatching and maximum size attained. However, overall mean size differed significantly between the two species, with E. clara being th e larger of the two. Elimia clara and E. cahawbensis had similar sex r atios (1.3 males: 1 female) throughout the year. Both species exhibite d sexual dimorphism in shell width with females being larger. Elimia c lara typically had a larger proportion of reproductively active female s. Each species maintained greater than 40 percent active females thro ughout the year, with peak activity in mid to late summer. Both specie s were mature at 5.5 mm shell width and were iteroparous. Elimia cahaw bensis had a higher prevalence of trematodes (Cotylomicrocercus sp.) t han did E. clara. Essentially, all infected females were unable to rep roduce. Both species of snails had the epizoic red alga, Boldia erythr osiphon, but significantly more of the E. clara population bore B. ery throsiphon than did the E. cahawbensis population.