See list Thylacodes arenarius is a species of sea snail, a marine gastropod mollusk in the family Vermetidae, the worm snails or worm shells.

[1] Shells of T. arenarius are irregular, and can reach a length of about 100–200 millimetres (3.9–7.9 in).

The visible part of the body is red with cream markings.

The foot of this mollusk is atrophied and it has lost its function of movement.

[4] This species can be found in the Mediterranean Sea - Eastern Basin[2] and in the North Atlantic Ocean - European waters.