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==Habitat==
==Habitat==
Nudibranchs live at virtually all depths, but they reach their greatest size and variation in warm, shallow waters.
Nudibranchs live at virtually all depths, but they reach their greatest size and variation in warm, shallow waters.
[[Image:Nudi from tidepool.jpg|thumb|Nudibranches (Hermissenda crassicornis) in Moss Beach, California.]]
[[Image:Nudi from tidepool.jpg|thumb|Nudibranchs (Hermissenda crassicornis) in Moss Beach, California.]]


==Description==
==Description==

Revision as of 20:16, 18 November 2007

Nudibranch
Spanish shawl, Flabellina iodinea
Scientific classification
Kingdom:
Animalia
Phylum:
Mollusca
Class:
Gastropoda
Subclass:
Orthogastropoda
Superorder:
Heterobranchia
Order:
Nudibranchia
Suborder:
Doridina

Dendronotina Arminina Aeolidina

See text for superfamilies.

A nudibranch; enPR: nōōʹdə-brăngk, nyōōʹdə-brăngk) is a name that is used for any one of a very large group of sometimes very colorful sea slugs.

(It is necessary to point out however, that not all "sea slugs" are nudibranchs. There are numerous kinds of sea slugs which belong to other, not very closely related, taxonomic groups, such as the heterobranch sea butterflies, sea angels, and sea hares, as well as the only very distantly related pelagic caenogastropod sea slugs in the superfamily Carinarioidea.)

Nudibranchs are soft-bodied, shell-less marine opisthobranch gastropod mollusks belonging to the suborder Nudibranchia, which is the largest suborder of the order Heterobranchia. There are more than 3,000 described species.

The word "nudibranch" comes from Latin nudus, naked, and Greek brankhia, gills.

Many nudibranchs are extraordinarily brightly colored and have striking forms.

Distribution

They occur worldwide.

Habitat

Nudibranchs live at virtually all depths, but they reach their greatest size and variation in warm, shallow waters.

Nudibranchs (Hermissenda crassicornis) in Moss Beach, California.

Description

The body forms of nudibranchs vary wildly, 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The adult form is without a shell or operculum (a bony plate covering the opening of the shell, when the body is withdrawn).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.

Life habits

Reproduction

Nudibranch eggs in Moss Beach, California.

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]

Feeding

They 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.

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. This enables the nudibranch to ward off potential predators.

Taxonomy

"Nudibranchia", from Ernst Haeckel's Artforms of Nature, 1904.

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

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.

Where to view nudibranchs

The Birch Aquarium at La Jolla, California, has the largest collection of nudibranchs on display in the U.S.A.

Footnotes

  1. ^ 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): 119-136.
  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): 83-97.{{cite journal}}: CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)

See Also

Hooded nudibranch

References

  • H. Wägele and R. C. Willan (September 2000). "Phylogeny of the Nudibranchia". Zoological Journal of the Linnean Society. 1 (1): 83–181.

Images

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