tube shell (tubshel)

A bivalve mollusk of the family Gastrochænidæ in a broad sense, or Tubicolidæ, as the watering-pot shell and related forms. They agree in secreting a shelly tube about the long siphons, and in extreme cases this formation makes them look very unlike ordinary bivalves. The case is like that of the related teredos or ship-worms. Both valves may be of considerable size and separate from the tube (see cut under Gastrochæna ), or one may be free from the tube and the other fixed to it, as in Clava gella; or both may be very small and soldered to a large tube of singular construction, as in the true watering pots. See cut under watering -pot.