VISUAL ORIENTATION TO GASTROPOD SHELLS BY CHEMICALLY STIMULATED HERMIT-CRABS, CLIBANARIUS-VITTATUS (BOSC)

Visually directed movements of the hermit crab Clibanarius vittatus (B osc) toward 6 species of gastropod shells were studied in a circular a rena with a white wall. The study tested the hypothesis that crabs vis ually discriminate between different species of shells. Only Investiga ting Crabs, those exhibiting chemically induced shell-investigation be havior, were tested. All trials were in the presence of chemical cues generated by freezing and thawing flesh from the gastropods Busycon ca rcia or Polinices duplicatus. Directional orientation orientation was absent when crabs were presented with the white background alone. Each shell was tested in different positions (e.g., anterior, posterior, u pside-down, lateral). Crabs were attracted to shells in 9 of the 18 te st conditions, with strongest attraction to Polinices duplicatus (post erior position) and Busycon contrarium (lateral position). Since attra ction was not related to shell height, width, or surface area, it was concluded that crabs can discriminate between shells and were most att racted to shells that attain larger sizes. In a second experimental se ries, shells of B. contrarium or P. duplicatus were presented simultan eously in different positions. Crabs could distinguish between both sp ecies in different positions. When these 2 shell species were presente d simultaneously, crabs were significantly attracted to P. duplicatus in the presence of the odor of either B. carica or P. duplicatus. Thus , these results support the hypothesis and further indicate that attra ction to a shell involves a complex interaction of proprioreceptive in put from the host shell, chemical cues indicating the availability of a new shell, and visual recognition of a particular shell species.