Nudibranch
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| Image:Spanish shawl.JPG Spanish shawl, Flabellina iodinea
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See text for superfamilies |
A nudibranch (pronounced /nudɪbɹaŋk/) is any member of a suborder of soft-bodied, shell-less marine opisthobranch gastropod mollusks noted for their often extraordinary colors and striking forms. The suborder, Nudibranchia, is the largest suborder of heterobranchs, with more than 3,000 described species.
The word "nudibranch" comes from Latin nudus, naked, and Greek brankhia, gills.
Nudibranchs are often casually called sea slugs, a non-scientific term which has led some people to believe that all sea slugs are nudibranchs. Although nudibranchs are very numerous in terms of species and are often very attractive, many other kinds of sea slugs exist, and they belong to several not very closely related taxonomic groups. There are other marine heterobranch shell-less gastropod groups: the Cephalaspidea sea slugs such as the colorful Aglajidae, and also the Sacoglossa, the sea butterflies, the sea angels, and the (often rather large) sea hares. The word sea slug is also sometimes applied to the only very distantly related, pelagic, caenogastropods within the superfamily Carinarioidea.
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[edit] Distribution
Nudibranchs occur worldwide.
[edit] Habitat
Nudibranchs live at virtually all depths, but they reach their greatest size and variation in warm, shallow waters.
[edit] Description
The body forms of nudibranchs vary enormously, but because they are opisthobranchs, unlike most other gastropods they are bilaterally symmetrical because they have undergone secondary detorsion.
They lack a mantle cavity.
They vary in adult size from 20 to 600 mm.
The adult form is without a shell or operculum (a bony or horny plate covering the opening of the shell, when the body is withdrawn).
The name nudibranch 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.
[edit] Life habits
[edit] Reproduction
Nudibranchs are hermaphroditic, and thus have a set of sex organs for both genders, but they can rarely fertilize themselves.
Nudibranchs typically deposit their eggs within a gelatinous spiral. [1]
[edit] Feeding
Nudibranchs are carnivorous. Some feed on sponges, others on hydroids, others on bryozoans, and some are cannibals, eating other sea slugs, or, on some occasions, members of their own species. There is also a group that feeds on tunicates and barnacles.
[edit] Colors in nudibranchs
Among this group can be found the most colorful creatures on earth. Because sea slugs, in the course of evolution, have lost their shell, they have had to evolve other means of defense. Some nudibranchs utilize camouflage through color patterns that make them invisible (cryptic behavior). Others warn off predators by being brightly colored, which serves to remind predators that they are distasteful or poisonous (aposematic behavior).
Champions in their colorful display are the Chromodorids. Nudibranchs that feed on hydroids store the hydroid's nematocysts (stinging cells) in the dorsal body wall, the cerata. This enables the nudibranch to ward off potential predators.
[edit] 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. On the basis of investigation of 18S rDNA sequence data, there has been found strong evidence for support of the monophyly of the Nudibranchia and its two major groups, the Anthobranchia/Doridoidea and Cladobranchia
- 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
A new study, published in May 2001, has again revised the taxonomy of the Nudibranchia [2]. They are thus divided into two major clades:
- Anthobranchia (= Bathydoridoidea + Doridoidea)
- Dexiarchia nom. nov. (= Doridoxoidea + Dendronotoidea + Aeolidoidea + “Arminoidea”).
The dorids (infraorder Anthobranchia) have the following characteristics: the branchial plume forms a cluster on the posterior part of the neck, around the eyes. 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 home. zooxanthellae.
[edit] Where to view nudibranchs
The Birch Aquarium at La Jolla, California, has the largest collection of nudibranchs on display in the U.S.A.
[edit] Footnotes
- ^ Klussmann-Kolb A (2001). "The Reproductive Systems of the Nudibranchia (Gastropoda, Opisthobranchia): Comparative Histology and Ultrastructure of the Nidamental Glands with Aspects of Functional Morphology". Zoologischer Anzeiger 240 (2).
- ^ Schrödl M.; Wägele H.2 Willan R.C. (2001). "Taxonomic Redescription of the Doridoxidae(Gastropoda: Opisthobranchia), an Enigmatic Family of Deep Water Nudibranchs, with Discussion of Basal Nudibranch Phylogeny". Zoologischer Anzeiger, 240 (1).
[edit] See also
[edit] References
- H. Wägele and R. C. Willan (September 2000). "Phylogeny of the Nudibranchia". Zoological Journal of the Linnean Society 1 (1): 83–181.
[edit] External links
- Lots of images and information on Australian nudibranchs
- Sea Slug Forum: many images and much valuable information worldwide
- Nudi Pixel: Online resource for nudibranchs and sea slugs identification using photographs
- Nudibranch gallery
- Bibliography and portal to opisthobranch, nudibranch & seaslug information
- Nudibranch photo gallery from Bali
[edit] Images
Godiva Quadicolor Wes Australia.jpg
Godiva quadricolor laying eggs, Swan River, Western Australia |
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Chromodoris lochi.jpg
Chromodoris lochi, Papua New Guinea |
Two Clown Nudibranchs.JPG
Two clown nudibranchs, New Zealand |
Notodoris minor.jpg
Notodoris minor on the ribbon reefs off Cooktown, Queensland, Australia |
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Chromodoris willani Lembeh.JPG
Chromodoris willani, Lembeh Straits, Indonesia |
Nembrotha kubaryana.JPG
Nembrotha kubaryana, Lembeh Straits, Indonesia |
Chromodoris annae.JPG
Chromodoris annae, Lembeh Straits, Indonesia |
Pteraeolidia ianthina1.JPG
Pteraeolidia ianthina, Lembeh Straits, Indonesia |
Nudibranch in tidepool.jpg
Clown nudibranch,Triopha catalinae, northern California |
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