Nudibranch
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Nudibranchs are sea slugs belonging to the suborder Nudibranchia, the largest suborder of the order Opisthobranchia. There are more than 3,000 described species.
Description
These sea slugs are jelly-bodied snails. The adult form is without a shell or operculum (a bony plate covering the opening of the shell, when the body is withdrawn).The word "nudibranch" comes from Latin nudus meaning "naked", and Greek branchia meaning "gills". The name is appropriate since the dorids (infraclass Anthobranchia) breathe through a branchial plume of bushy extremities on their back, rather than using gills. By contrast, on the back of the aeolids in infraclass Cladobranchia there are brightly colored sets of tentacles called cerata.
Nudibranchs have cephalic (head) tentacles, which are sensitive to touch, taste, and smell. Club-shaped rhinophores detect the odors.
They are hermaphroditic, but can rarely fertilize themselves.
They are carnivorous. Some feed on sponges, others on hydroids, others on bryozoans, and some are cannibals, eating members of their own species. There is also a group that feeds on tunicates and barnacles.
Body forms can vary wildly. They lack a mantle cavity. Their size varies from 4 to 600 millimetres.
They occur worldwide at all depths, but they reach their greatest size and variation in warm, shallow waters.
Among them, you can find the most colorful creatures on earth. Because sea slugs, in the course of evolution, have lost their shell, they have had to evolve another means of defense: camouflage, through color patterns that make them invisible (cryptic behavior) or warn off predators as being distasteful or poisonous (aposematic behavior). Champions in their colorful display are the Chromodorids. The nudibranchs that feed on hydroids store the hydroid's nematocysts (stinging cells) in the dorsal body wall. This enables the nudibranch to ward off potential predators.
Taxonomy
The taxonomy of the Nudibranchia is still evolving. Many taxonomists used to treat Nudibranchia as an order, based on the authoritative work of Johannes Thiele (1931), who built on the concept of Henri Milne-Edwards (1848). But new insights through morphological data and gene-sequence research, cause some confidence in the congruence of the data sets of the new and the old.
- Infraorder Anthobranchia Férussac, 1819 (dorids)
- *Superfamily Doridoidea Rafinesque, 1815
- *Superfamily Doridoxoidea Bergh, 1900
- *Superfamily Onchidoridoidea Alder & Hancock, 1845
- *Superfamily Polyceroidea Alder & Hancock, 1845
- Infraorder Cladobranchia Willan & Morton, 1984 (aeolids)
- *Superfamily Aeolidioidea J. E. Gray, 1827
- *Superfamily Arminoidea Rafinesque, 1814
- *Superfamily Dendronotoidea Allman, 1845
- *Superfamily Metarminoidea Odhner in Franc, 1968
The aeolids (infraorder Cladobranchia) have the following characteristics: Instead of the branchial plume, they have cerata. They lack a mantle. Only species of the Cladobranchia are reported to house zooxanthellae.
The Birch Aquarium at La Jolla, California, has the largest selection of nudibranches on display in the entire world.
Reference
External links
- [www.nudibranch.com.au] lots of images and info
- [somewhat outdated taxonomy]
- [Sea Slug Forum] many images and much information
Images
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