Onustus longleyi is a species of large sea snail, a marine gastropod mollusk in the family Xenophoridae, the carrier shells.

Their spire is rather smooth, and the lower edge of the shell is quite irregular and jagged.

A "glue" or mucus is secreted from the outer portion of their body, called the mantle or pallium in Latin, which means cloak or robe.

It is constantly secreted to enlarge the spiral shell, in a 360-degree manner, as the soft-bodied snail grows.

Their embryos develop into planktonic trochophore larvae, and later into juvenile veligers before becoming fully grown adults.

These carnivores consume low growing organisms, such as low-growing grasses and algae.

The animals move by extending their powerful foot, anchoring the end in the substrate with the operculum (gill cover), and jerking the shell forward in a leaping movement.

Onustus longleyi is distributed along the American Atlantic coast from North Carolina to the Gulf of Mexico and the Caribbean reaching Brazil in the South.