Scaphopod

This post concerns scaphopods, which are mollusks that belong to the same phylum as snails, squids, octopi, etc. Scaphopods are tusk-shaped shells that are partially infaunal, that is to say they burrow into the ocean floor but do not burrow deep enough to cover the top part of their shell.

The drawing shows how the shell projects into the sediment. The mouth is surrounded by feeding tentacles which bring microscopic-sized food to it. The gut is straight. Water is brought down into the shell and also is excreted through a hole at the top of the shell.

This is a fossil scaphopod of the Eocene Dentalium stramineum The specimen is 7 cm long and almost complete. It is from Simi Valley, southern California. Fossil scaphopods are not common. 

This is a modern specimen of Dentalium. If it were not for modern specimens, scientists would probably never have determined that these simple tubes were made by mollusks.

This is another modern specimen of Dentalium.