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This contribution provides novel information on the anatomy, radula and phylogeny of several species of PhaenomenellaFraussen & Hadorn, 2006, a genus of Buccinoidea Rafinesque, 1815 with unclear affinities. Molecular phylogenetic analysis based on sequences of mitochondrial COI and nuclear 28S rRNA genes of different representatives of Buccinoidea revealed close relationships of Phaenomenella with Siphonalia A. Adams, 1863 both taxa forming a clade with maximal support. The anatomy of two species of the latter genus was examined for the first time for comparative purposes. The subfamily Siphonaliinae Finlay, 1928 was erected for several Recent and fossil genera of Southern Hemisphere Buccinidae Rafinesque, 1815, and is still recognized by current taxonomists (Bouchet et al. 2017). Species of all Recent genera of Siphonaliinae were included in our analysis and the monophyly of the subfamily Siphonaliinae in its original scope is rejected. Molecular and morphological data revealed two still unnamed species of Phaenomenella from the lower bathyal zone of the South China Sea. These species, Phaenomenella nicoi n. sp. and P. samadiae n. sp. are described in the present study.

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.