Vermetidae
The Vermetidae, the worm snails or worm shells, are a taxonomic family of small to medium-sized sea snails, marine gastropod molluscs in the clade Littorinimorpha.[1] The shells of species in the family Vermetidae are extremely irregular, and do not resemble the average snail shell, hence the common name "worm shells" or "worm snails".
The empty calcareous tubes of certain marine annelid tube worms, for example the Serpulidae, can sometimes be casually misidentified as empty vermetid shells, and vice versa. The difference is that vermetid shells are shiny inside and have three shell layers, whereas the annelid worm tubes are dull inside and have only two shell layers.
The Vermetidae were recognized as the only family in the superfamily Vermetoidea in the taxonomy of Bouchet & Rocroi (2005) within the clade Littorinimorpha.
This classification of the Vermetoidea has been controversial. Studies, based on sperm ultrastructure,[2] and on molecular data[3] clearly place it within the clade Littorinimorpha. However, there are still a number of authors[4][5][6] that place it within the superfamily Cerithioidea. The genera Campanile and Thylacodes form a clade that is sister to the Cerithioidea, as shown in a study by Lydeard et al. (2002).[7]
Bandel (2006)[8] established a new subfamily Laxispirinae as one of three subfamilies he recognized within the Vermetidae:
