[1][3] Members of the genus Waldo have small shells (less than 5 mm (0.20 in) in length) that are ovate to trapezoidal in shape.

The shell sculpture consists of commarginal grooves (striae), though weakly to moderately-defined radial ribs may also be present.

The outer organic layer of the shell (the periostracum) can be thin to thick, and translucent to white in coloration.

[1] The mantle covers most of the outer shell surface and possesses small rounded protuberances (papillae).

[1] All members of the genus Waldo are believed to be obligate commensal epibionts of echinoids (sea urchins).

[1] Adults are actively mobile, crawling freely about the external surfaces of their hosts with their large feet, much like snails.