Sea slug

A sea slug is a marine gastropod mollusk whose adult form usually lacks a conspicuous external shell. The name covers several groups, including nudibranchs and sea hares.

Gastropoda: The mollusk class that includes snails, slugs, limpets, and related animals. Sea slugs are gastropods whose body plans have evolved in marine lineages.
Cerata: Finger-like projections on some sea slugs that increase surface area and may aid respiration or defense. Many nudibranchs use cerata for gas exchange and, in some species, defense.
Aplysia californica: A large sea hare species used extensively in research on learning and memory. Its large, accessible neurons enabled influential experiments on the cellular basis of learning.
Land slug: A terrestrial gastropod mollusk with no conspicuous external shell. Land slugs resemble sea slugs in shell reduction but evolved for life on land.
Nudibranch: A shell-less marine gastropod with exposed gills or other respiratory structures on its back. Nudibranchs are one of the best-known groups commonly called sea slugs.
Kleptocnidae: Stolen stinging capsules retained by some nudibranchs after they eat cnidarians. These capsules let certain sea slugs reuse prey defenses against their own predators.
Eric Kandel: A neuroscientist who studied learning and memory using the sea hare Aplysia. Kandel's Aplysia research connected changes at synapses with behavioral learning.
Sea snail: A marine gastropod that typically retains a conspicuous external shell. Sea snails show the shelled marine gastropod form contrasted with most sea slugs.
Sea hare: A large marine gastropod with soft, ear-like sensory appendages and reduced internal shell. Sea hares are another major group included under the broad name sea slug.
Kleptoplasty: The retention of functional algal chloroplasts inside the cells of an animal that has eaten algae. Some sacoglossan sea slugs retain chloroplasts and gain temporary photosynthetic activity.

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