Aplysiida

Aplysiida is an order of marine gastropod molluscs commonly called sea hares. Its members have reduced internal shells or lack shells entirely.

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Gastropoda: Gastropoda is the largest class of molluscs, including snails, slugs, limpets, and sea hares. Aplysiida is classified within this diverse mollusc class.
Aplysia californica: Aplysia californica is a large Pacific sea hare used extensively in neuroscience research. Its well-studied nervous system illustrates the biology of a sea hare in detail.
Eric Kandel: Eric Kandel is a neuroscientist whose research on learning and memory helped establish cellular mechanisms of memory. His work using Aplysia connected sea hare neurons to lasting changes in behavior.
Aplysia: Aplysia is a genus of large sea hares found in warm and temperate seas. It includes the best-known sea hare species and prominent laboratory models.
Opisthobranchia: Opisthobranchia is a traditional grouping of marine gastropods characterized by posterior or exposed gills and varied shell reduction. Sea hares were historically placed among these shell-reduced marine gastropods.
Ink gland: An ink gland is a defensive organ that releases colored secretion in some marine invertebrates. Many sea hares release purple ink when threatened.
Aplysia gill-withdrawal reflex: The Aplysia gill-withdrawal reflex is a defensive response in which the animal retracts its gill after stimulation. Experiments on this reflex revealed cellular mechanisms of habituation and sensitization.
Dolabella auricularia: Dolabella auricularia is a sea hare with a broad, rounded body and a small internal shell. Its squat shape distinguishes it from the more elongated Aplysia species.
Mantle (mollusc): The mantle is a mollusc’s tissue layer that covers the body and often secretes the shell. In sea hares, mantle tissue can conceal a small internal shell or remain shell-less.
Opaline gland: The opaline gland is a sea hare organ that releases a milky secretion during defensive responses. Its secretion can distract predators and interact with the ink released nearby.