Scaphopoda

Scaphopoda, which are called tusk shells in English is a class of marine molluscs. The name of the class can be translated as shovel-footed. These animals vary in size, most are small though. These animals usually do not live in the tidal zone, they dig themselves into muddy or sandy ocean floors, up to a depth of about 700m. There are about 500 recent species. Fossils of over 900 species have been described. As of 2009, it is unclear how many of these descriptions are valid species. 
These species live in an elongated tube, which is open on both ends, but which can be closed on one end. The animal lives inside the tube, and is attached to it. Scaphopoda do reproduce sexually.