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Nudibranch
Nudibranchs (/ˈnjuːdɪbræŋk/) are a group of soft-bodied marine gastropod molluscs, belonging to the order Nudibranchia, that shed their shells after their larval stage. They are noted for their often extraordinary colours and striking forms, and they have been given colourful nicknames to match, such as "clown", "marigold", "splendid", "dancer", "dragon", and "sea rabbit". About 3,000 species of nudibranchs are known.
The word nudibranch comes from the Latin nudus 'naked' and the Ancient Greek βράγχια (bránkhia) 'gills'.
Nudibranchs are often casually called sea slugs, as they are a family of opisthobranchs (sea slugs), within the phylum Mollusca (molluscs), but many sea slugs belong to several taxonomic groups that are not closely related to nudibranchs. A number of these other sea slugs, such as the photosynthetic Sacoglossa and the colourful Aglajidae, are often confused with nudibranchs.
Nudibranchs occur in seas worldwide, ranging from the Arctic, through temperate and tropical regions, to the Southern Ocean around Antarctica. However, they are mostly found around Southeast Asia. They are almost entirely restricted to salt water, although a few species are known to inhabit lower salinities in brackish water.
Nudibranchs live at virtually all depths, from the intertidal zone to depths well over 700 m (2,300 ft). The greatest diversity of nudibranchs is seen in warm, shallow reefs, although one nudibranch species was discovered at a depth near 2,500 m (8,200 ft). This nudibranch, described in 2024 as Bathydevius, is the only known nudibranch with a bathypelagic lifestyle and is one of the very few to be bioluminescent.
Nudibranchs are benthic animals, found crawling over the substrate. The only exceptions to this are the neustonic Glaucus nudibranchs, which float upside down just under the ocean's surface, such as the glaucus atlanticus; the pelagic nudibranchs Cephalopyge trematoides, which swim in the water column; the two pelagic species of Phylliroe, and the evolutionarily distinct, bathypelagic Bathydevius.
The body forms of nudibranchs vary greatly. Because they are opisthobranchs, unlike most other gastropods, they are apparently bilaterally symmetrical externally (but not internally) because they have undergone secondary detorsion. In all nudibranchs, the male and female sexual openings are on the right side of the body, reflecting their asymmetrical origins. They lack a mantle cavity. Some species have venomous appendages (cerata) on their sides, which deter predators. Many also have a simple gut and a mouth with a radula.
The eyes in nudibranchs are simple and able to discern little more than light and dark. The eyes are set into the body, are about a quarter of a millimeter in diameter, and consist of a lens and five photoreceptors.
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Nudibranch
Nudibranchs (/ˈnjuːdɪbræŋk/) are a group of soft-bodied marine gastropod molluscs, belonging to the order Nudibranchia, that shed their shells after their larval stage. They are noted for their often extraordinary colours and striking forms, and they have been given colourful nicknames to match, such as "clown", "marigold", "splendid", "dancer", "dragon", and "sea rabbit". About 3,000 species of nudibranchs are known.
The word nudibranch comes from the Latin nudus 'naked' and the Ancient Greek βράγχια (bránkhia) 'gills'.
Nudibranchs are often casually called sea slugs, as they are a family of opisthobranchs (sea slugs), within the phylum Mollusca (molluscs), but many sea slugs belong to several taxonomic groups that are not closely related to nudibranchs. A number of these other sea slugs, such as the photosynthetic Sacoglossa and the colourful Aglajidae, are often confused with nudibranchs.
Nudibranchs occur in seas worldwide, ranging from the Arctic, through temperate and tropical regions, to the Southern Ocean around Antarctica. However, they are mostly found around Southeast Asia. They are almost entirely restricted to salt water, although a few species are known to inhabit lower salinities in brackish water.
Nudibranchs live at virtually all depths, from the intertidal zone to depths well over 700 m (2,300 ft). The greatest diversity of nudibranchs is seen in warm, shallow reefs, although one nudibranch species was discovered at a depth near 2,500 m (8,200 ft). This nudibranch, described in 2024 as Bathydevius, is the only known nudibranch with a bathypelagic lifestyle and is one of the very few to be bioluminescent.
Nudibranchs are benthic animals, found crawling over the substrate. The only exceptions to this are the neustonic Glaucus nudibranchs, which float upside down just under the ocean's surface, such as the glaucus atlanticus; the pelagic nudibranchs Cephalopyge trematoides, which swim in the water column; the two pelagic species of Phylliroe, and the evolutionarily distinct, bathypelagic Bathydevius.
The body forms of nudibranchs vary greatly. Because they are opisthobranchs, unlike most other gastropods, they are apparently bilaterally symmetrical externally (but not internally) because they have undergone secondary detorsion. In all nudibranchs, the male and female sexual openings are on the right side of the body, reflecting their asymmetrical origins. They lack a mantle cavity. Some species have venomous appendages (cerata) on their sides, which deter predators. Many also have a simple gut and a mouth with a radula.
The eyes in nudibranchs are simple and able to discern little more than light and dark. The eyes are set into the body, are about a quarter of a millimeter in diameter, and consist of a lens and five photoreceptors.