Modulus tectum: Modulus tectum (Gmelin, 1791). Length, 18mm; diameter, 20 mm. Shell: turbinate, solid; with axial ribbing; cream-colored. Spire: last whorl large, bulbous but angular; apical whorls flat; suture impressed. Sculpture: weak spiral ribs and stronger axial ribs. Aperture: quadrangular, lirate, outer lip thin; a projecting tooth at the base of the columella; operculum circular and transparent. Color: white with occasional brown splashes. Animal: foot green; mantle edged with green and brown; proboscis dark green, tentacles pale green.
These mollusks are common in sand or algal-sand mats in tide pools and on benches, and have been dredged from depths of 100 m. The shells are often covered with heavy growths of algae.
M. tectum occurs throughout the Indo-West Pacific.