Appearance
T. testudinalis has a low domed shell, oval in outline. It can grow to up to 30 x 24 x 10 mm but typically is about half this size. The apex is towards the anterior of the shell and fine ridges radiate from it. The shell is banded with brown and white. The mantle is the part of the body wall immediately under the shell and at the edges it is curled round to form a collar. The foot is broad and oval. The head bears two sensory tentacles with a tiny black eye at the base of each.

