Planaxidae

Planaxidae is a family of marine gastropod mollusks commonly referred to as planaxid snails. The group comprises multiple genera, with Planaxis being the best known. Members of the family are generally small to medium in size and possess elongated, often glossy shells that show varying degrees of axial or spiral sculpture. The aperture is commonly elongated, and many species have a siphonal canal, reflecting their predatory or scavenging habits.

Distribution and habitat

Planaxids occur in warm and temperate seas worldwide, with a concentration in tropical and subtropical regions. They are typically found in shallow coastal environments, including sandy and muddy substrates, intertidal zones, seagrass beds, and sometimes mangrove margins. They may be encountered from the lower intertidal zone to modest depths, often in areas with ample detritus or microalgae.

Ecology and behavior

Planaxidae snails are usually detritivores and scavengers, feeding on microalgae, diatoms, and organic matter. Some species may prey on small invertebrates or opportunistically exploit available resources. They are generally active during periods of higher moisture, at night, or under overcast conditions when exposure to desiccation is minimized.

Life cycle

Reproduction varies among species, but many planaxids lay eggs in gelatinous capsules or masses. Larval development commonly includes a free-swimming veliger stage, facilitating dispersal, though some taxa may exhibit direct development.

Taxonomy

Planaxidae is a recognized family of caenogastropod gastropods, although its precise placement has varied across classifications. Some authorities have treated Planaxidae as an independent family, while others have included it as a subfamily within Cerithiidae or related groups. Modern treatments increasingly rely on molecular data to clarify relationships within this lineage.

Fossil record

The family has a fossil record that helps trace its evolutionary history in marine settings.