Cyclostrema subexcavatum is a species of sea snail, a marine gastropod mollusk in the family Liotiidae.[1]
(Original description by G.W. Tryon) The height of the shell attains 2.2 mm. The umbilicus is wide, perspective and shallow. The shell is whitish under a yellowish brown, membraneous epidermis. The spire is scarcely raised. The 4 whorls increase rather slowly until the last, which is rather large. The suture is broadly, angularly impressed. A little below the suture there is a bluntly angulated spiral keel. And on the middle of the base, towards the oblique aperture there is another keel. The thin peristome is simple.[2]
This marine species occurs off Puerto Rico at a depth of about 700 m.