Parasitic gastropods of the genus Annulobalcis Habe, 1965 (family Eulimidae), associated with the crinoids (comatulids) are common in Nhatrang Bay (Southern Vietnam). Morphological examination of Annulobalcis specimens, collected in this area revealed four distinct forms, significantly different also in host specificity. Mitochondrial cox1 sequence data have shown these forms to comprise four distinct species, their relationships are discussed. As a result of morphological and molecular studies, four new species of the genus Annulobalcis are described: A. albus n. sp., A. wareni n. sp., A. maculatus n. sp., and A. vinarius n. sp. The three former species appeared to be strictly species specific in their choice of host (parasitizing a single host species each), while the latter was found on a number of hosts, although mostly on a single species. Speciation in relation to host specificity of Annulobalcis is discussed.