Gastéropodes

Gastéropodes, or gastropods, are a highly diverse class of mollusks that includes most snails and slugs. They occupy marine, freshwater, and terrestrial environments and range from microscopic to large. A defining trait is the development of a univalve shell in many species, though numerous slugs have a reduced or absent shell. Torsion, a 180-degree twist of the visceral mass during larval development, is a hallmark of many gastropods and reshapes the arrangement of internal organs.

Anatomy and feeding: The muscular foot glides for locomotion, and a radula—a ribbon of microscopic teeth—is used for scraping or cutting food. The mantle cavity typically houses gills or a lung, and many species possess an operculum, a hard plate that can close the shell opening.

Ecology: Gastéropodes play important roles as grazers, detritivores, and predators in ecosystems. They are common on rocky shores, coral reefs, seagrass beds, freshwater bodies, and damp terrestrial habitats. Some species are edible and others are agricultural pests. Their shells provide protection for juveniles and shelter for other organisms after death.

Reproduction and life cycles: Reproductive strategies vary; many gastropods are hermaphroditic, while others are dioecious. Fertilization can be internal or external, and eggs are laid in capsules or gelatinous masses. In marine species, early development often includes trochophore and veliger larval stages; many land and freshwater forms have direct development.

Taxonomy and evolution: Gastéropoda is one of the largest molluscan classes, with tens of thousands of described species. Major lineages include Vetigastropoda, Caenogastropoda, and Heterobranchia. The fossil record extends back to the late Cambrian, making gastropods among the earliest and most enduring molluscan groups.