Asolene (Pomella) megastoma (Sowerby, 1825)

Asolene (Pomella) megastoma. Uruguay River, São Borja city, Rio Grande do Sul, Brasil. 25-01-2000. 77 mm high.	Asolene (Pomella) megastoma. Uruguay River, São Borja city, Rio Grande do Sul, Brasil. 25-01-2000. 73 mm high.

Shell: Very large shell (up to 100mm height), as wide as high with a very large mouth, even larger than the body whorl. The spire is depressed and nearly invisible from the front In largers shells, the spire can be heavily erroded.
The shell is relatively thick and heavy, although it might look fragile at first. The surface is rough and the umbilicus is very narrow to closed.
The colour varies from green to light brown without or only with a very faint banding pattern. The shell is white, with a faint violet at the inside.

Interactive 3D-models (Java): - Asolene megastoma shell

Operculum: The operculum is moderately thick and corneous. The structure is concentric with the nucleus close the centre of the shell. The colour is dark brown to black. The operculum can be retracted in the aperture (shell opening).

Asolene (Pomella) megastoma.	Asolene (Pomella) megastoma.

Body: Brown to nearly black with yellow spots on the back of the foot and around the head.
The head is relatively broad (the eyes and the tentacles are far apart) and the tentacles are of medium length and are quite thick. The eyes are rather small comared with other Ampullarids.
Eggs: The eggs are laid out of the water in a pinkish calcareous mass attached on vegetation or rocks. (observed by: Fabio Faraco, Brasil and Manuel G. Quintana, Argentina).

Behaviour: Asolene megastoma mainly resides on the bottom and in shadow rich places of its habitat. The shell is kept close to the ground and due to its flat shell shape and its large foot, it's hard to remove the snail from a solid surface. Not surprisingly for a snail that lives in rivers and streams with strong currents at times.
The broad head, with the eyes and tentacles on the outher ends, enables the snail to keep the eyes out of the shell, while the shell border touches the surface in front of the snail.
Distribution: Southeastern of Brasil: the Rio Uruguay system.

With thanks to Fabio Faraco for providing the shells which are displayed on this page.

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