Creeping Ancylid

The creeping ancylid is an extremely rare, native mollusk.

Creeping ancylid mollusk. Robert Aguilar/Smithsonian Environmental Research Center

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About This Species

Ancylids are grazers with diatom-rich diets. They are capable of self-fertilization. 

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Physical Characteristics

The shell of the creeping ancylid is limpet-like and small, up to 7 mm in length, 4 mm in width, and 3 mm in height, with parallel sides. It ranges in thickness, depending on environmental conditions, but is extremely fragile. The shell has a convex anterior slope and gently concave posterior slope. Its apex is flattened and leans slightly to the right. The shell color is light with faint radial striations (stripes).

Habitat

​The creeping ancylid clings to rocks, cobbles, mussel shells, and macrophytes (larger aquatic plants) in rivers, streams, and northern lakes. It seems to do best in cooler, well-oxygenated waters in its northernmost range. The creeping ancylid is found in the Arkansas, Colorado, Platte, Rio Grande, and Yampa River drainages. It ranges throughout most of North America east of the Rockies.

Additional Information

This mollusk is extremely rare. If you think you have found this species, please report your sighting to Colorado Parks and Wildlife.

Mollusk
Ferrissia rivularis