They are true Pectinibranchia which have taken to a pelagic life, and the peculiarities of structure which they exhibit are strictly adaptations consequent upon their changed mode of life.
Leydig, that the otocysts of Pectinibranchia even when lying close upon the pedal ganglion (as in fig.
The alimentary canal of the Pectinibranchia presents little diversity of character, except in so far as the buccal region is concerned.
Dium or olfactory Yet in some Pectinibranchia (Paludina) organ).
In other Pectinibranchia (and such variations are representative for all Mollusca, and not characteristic only of Pectinibranchia) we find that there is a very unequal division of the egg-cell at the commencement of embryonic development, as in Nassa.
The Pectinibranchia the pedal nerves are br, Ctenidium (branchial distinctly nerves given off from the pedal plume).
The sub-class is now divided into two orders: the Aspidobranchia in which the branchia or ctenidium is bipectinate and attached only at its base, and the Pectinibranchia in which the ctenidium is monopectinate and attached to the mantle throughout its length.
In the tribe of Pectinibranchia called Heteropoda the foot takes the form of a swimming organ.