This is not always the case with Lamellibranchs; there is in the group a tendency for the corresponding edges of the mantle-skirt to fuse together by concrescence, and so to form a more or less completely closed bag, as in the Scaphopoda (Dentalium).
An additional class was instituted for the reception of Dentalium and its few allies, and for this class Bronn's name Scaphopoda was used.
The Lamellibranchia are no longer regarded as a distinct branch in contrast to the remaining Mollusca; according to Pelseneer they are allied to the Gastropoda and Scaphopoda, all three classes being derived from a common hypothetical ancestor, called Prorhipidoglossum.
In the Scaphopoda there is no distinct genital duct, the relations are as in Aspidobranchia.
In Polyplacophora there are eight on each side (8.I.8); in Scaphopoda two on each side (2.I.2); in almost all Cephalopoda three on each side (3.I.3); in Gastropoda the number varies very much in different subdivisions.
SCAPHOPODA, the third of the five classes into which the Phylum Mollusca is divided.'
The Scaphopoda are marine Molluscs with the body, especially the foot, adapted to a burrowing life in sand.
It is remarkable that in Scaphopoda only among Mollusca the blood-spaces are in communication with the external medium: a pair of apertures near the renal openings lead from the perianal sinus to the exterior and allow the blood to escape during violent contractions of the body.
- Scaphopoda feed on the lowest marine organisms such After Kowalewsky, in Lanas Diatoms, Protozoa, &c. There are 150 's Treatise on Zoology, living and about 275 known fossil species.