Annulobalcis maculatus

Abstract: The host preference of the symbiotic gastropods Annulobalcis albus, Annulobalcis vinarius and Annulobalcis maculatus in the family Eulimidae for their crinoid hosts was studied experimentally. Y-tubes of plexiglas allowed us to investigate the effect of chemical factors. Sea-water from aquaria containing different crinoids, or similar sea-water from aquaria without crinoids was fed into the distal parts of the Y-tube. From the results, we concluded that probably all the tested eulimids can recognize their hosts. Two are strictly host specific in nature, Annulobalcis albus and Annulobalcis maculatus, and they more often selected the water coming from the aquarium containing their hosts. They responded weakly to water from the aquarium without any crinoids. The third species, Annulobalcis vinarius, which in nature is not strictly host specific, preferred the crinoid Himerometra robustipinna (its main host) over Comatella nigra and Stephanometra tenuipinna (its alternative hosts) on which it is less often found in nature. These molluscs probably use Comatella nigra and Stephanometra tenuipinna as a reserve hosts and rarely colonize them. While chemoreception appears to be the major mechanism of host selection, the tested molluscs often demonstrated no reaction and this suggest that they do not need to settle on the crinoids immediately and that the symbiosis is facultative.