Clionella semicostata is a species of sea snail, a marine gastropod mollusk in the family Clavatulidae.

The shoulder angle is situated above or at the middle of the whorl.

The yellowish-brown to dark brown periphery of the shell is nodulous by the terminations of short, oblique, rather distant axial ribs (numbering 12-14).

The color of the shell is a uniform light yellowish brown.

[3] This marine species occurs from False Bay to Cape Agulhas, South Africa