The order is now divided into two sub-orders: the Taenioglossa, in which there are three teeth on each side of the median tooth of the radula, and the Stenoglossa, in which there is only one tooth on each side of the median tooth.
The gland has been found in both sub-orders of the Pectinibranchia, in Cyclostoma and Cypraea among the Taenioglossa, in Hemifusus, Cassis, Nassa, Murex, Fasciolariidae, Turbinellidae, Olividae, Marginellidae and Conidae among the Stenoglossa.
Normal Taenioglossa of creeping habit.
Pelagic Taenioglossa with foot large and laterally compressed to form a fin.
These all possess a fully developed gill-plume and are typical Pectinibranchs of the sub-order Taenioglossa, most of the members of which are marine.