Cystiscus

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Cystiscus is a genus of very small sea snails (micromollusks) in the family Cystiscidae. Some scientists place it in Marginellidae.

What they are like
- Size and shell: tiny to small shells, usually white and glossy, often barely visible spires. Length about 1–6 mm.
- Shape and surface: shell shapes are usually elliptic or oblong; the surface is smooth with little to no pattern.
- Aperture and lip: the opening is narrow to broad, and the lip is thickened.
- Internal features: the columella (the inner lip) has multiple folds (commonly 2–8, sometimes more) with parietal lirae; many species have a strong first fold.
- Mantle and color: the mantle is smooth and can extend over the shell; body colors are often bright (red, orange, yellow, brown, or black) and can show through the shell.
- Radula: has a long, uniserial ribbon with 80–209 plates; plates have sharp cusps.
- Habitat: living from the intertidal zone down to about 370 meters deep; there are fossil records from the Eocene to Miocene.
- Distinguishing features: a long siphon helps distinguish Cystiscus from similar snails like Gibberula.
- Diversity: there are many described species within Cystiscus.