However, it wasn't until the discovery of the hot vent communities in the deep-sea in the mid1970s that diversity and abundances of gastropods associated with low oxygen conditions was truly appreciated.
Vents are geologically old structures.
Arguments for the antiquity of taxa associated with vents are often based on fossil occurrences of taxonomically similar taxa. However this similarity has not been rigorously tested to determine whether or not it reflects relatedness. Other evidence marshaled in support of this antiquity is based on bizarre and supposedly archaic character combinations found in members of the hot vent faunas. Morphological and developmental characters were used to reassess the phylogenetic relationships of the Gastropods. The analysis used 117 characters and includes 40 gastropod taxa.