Nudibranch
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Nudibranchs (Nudibranchia), form the largest suborder of the order Opisthobranchia, subclass Orthogastropoda, class Gastropoda in the phylum Mollusca. The Nudibranchs are represented by more than 3,000 species.
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Description
These sea slugs are jelly-bodied snails. The adult form is without a shell or operculum (= bony plate covering the opening of the shell, when the body is withdrawn).
The word ‘nudibranch’ comes from New Latin "Nudibranchia". The Latin word "nudus", means naked, and the Greek word "branchia" means gills. Thus, nudibranch translates to "naked gills", which is appropriate since the dorids breathe through a branchial plume, bushy extremities on their back, rather than using gills. On the back of the aeolids are three brightly colored sets of tentacles called cerata.
Nudibranchs have cephalic (i.e. situated on the head) tentacles, which are sensitive to touch, taste, and smell (club-shaped rhinophores detect the odors).
They are hermaphroditic, but cannot fertilize themselves. They are carnivorous. Some feed on sponges, others on hydroids, others on bryozoans. 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 mm to 60 cm.
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 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.
Taxonomy
The taxonomy of the Nudibranchia is still evolving. Many taxonomists used to treat the Nudibranchia as an order, based on the authoritative work of J. Thiele (1931), who built on the concept of 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.
Subclass Orthogastropoda Ponder & Lindberg, 1997 (earlier Prosobranchia, Opisthobranchia)
Superorder Heterobranchia J.E. Gray, 1840
- Order Opisthobranchia Milne-Edwards, 1848
- Suborder Nudibranchia Blainville, 1814 (nudibranchs)
- 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 dorids (infraorder Anthobranchia) have following characteristics : the branchial plume forms a cluster on the posterior part of the back, around the anus. Fringes on the mantle do not contain any intestines.
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.
Reference
H. WÄGELE; R.C. WILLAN : Phylogeny of the Nudibranchia :Zoological Journal of the Linnean Society September 2000, vol. 1 no.1, pp. 83-181(99)
External link
- Excellent, but somewhat outdated taxonomy (http://www.seaslug.com/system.html)
- sea slug forum (http://www.seaslugforum.net/welcome.htm) many excellent images and much interesting information
- New Zealand Nudibranch Images (http://www.ianskipworth.com/suig/nudis.html)