Berghia coerulescens
A pair of Chromodoris lochi from Puerto Galera, the Philippines.
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Gastropoda
(unranked): clade Heterobranchia

clade Euthyneura
clade Nudipleura
clade Nudibranchia


See text for superfamilies

A nudibranch /ˈnjdɨbræŋk/[1] is a member of what is now a taxonomic clade, and what was previously a suborder, of soft-bodied, marine gastropod mollusks which shed their shell after their larval stage.[2] They are noted for their often extraordinary colors and striking forms. The clade Nudibranchia is the largest clade within the heterobranchs, with more than 3,000 described species.

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

Nudibranchs are often casually called "sea slug", but many sea slugs belong to several taxonomic groups which are not related to nudibranchs. A number of these other sea slugs (such as the colorful Aglajidae) are often confused with nudibranchs.



Nudibranchs occur in seas worldwide.


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


Aeolidiella stephanieae. Typical body of a nudibranch with cerata consist of:
ot = oral tentacles,
ft = foot tentacles,
e = eye,
r = rhinophores,
c = cerata. This species has cnidosacs at the cerata tips.

The body forms of nudibranchs vary a great deal, but because they are opisthobranchs, unlike most other gastropods they are bilaterally symmetrical both externally and internally because they have undergone secondary detorsion. They lack a mantle cavity. Some species have venomous appendages (cerata) on their sides which are used to deter predators. Many also have a simple gut and a mouth with a radula.

Their eyes are simple and able to discern little more than light and dark.[3] The eyes are set into the body, are about a quarter of a millimeter in diameter, and consist of a lens and five photoreceptors.[4]

They vary in adult size from 20 to 600 millimetres (0.79 to 24 in).

The adult form is without a shell or operculum (in shelled gastropods the operculum is a bony or horny plate that can cover the opening of the shell when the body is withdrawn).

The name nudibranch is appropriate, since the dorids (infraclass Anthobranchia) breathe through a "naked gill" shaped into branchial plumes in a rosette on their backs.[5] By contrast, on the back of the aeolids in the clade Cladobranchia there are brightly colored sets of protruding organs called cerata.

Nudibranchs have cephalic (head) tentacles, which are sensitive to touch, taste, and smell. Club-shaped rhinophores detect odors.

Life habits


Acanthodoris lutea laying eggs

Nudibranchs are hermaphroditic, and thus have a set of reproductive organs for both sexes, but they cannot fertilize themselves.[6]

Nudibranchs typically deposit their eggs within a gelatinous spiral.[7]


Solar powered Pteraeolidia ianthina have adapted cerata to contain zooxanthellae which continue to photosynthesize and provide energy to the nudibranch.

All known nudibranchs are carnivorous.[6] Some feed on sponges, others on hydroids,(e.g. Cuthona)[8] others on bryozoans (phanerobranchs such as Tambja, Limacia, Plocamopherus and Triopha),[9] and some eat other sea slugs or their eggs (e.g. Favorinus)[10] or, on some occasions, are cannibals and prey on members of their own species. Other groups feed on tunicates (e.g. Tambja, Nembrotha, Polycera, Thecacera),[11] other nudibranchs (Roboastra, which are descended from tunicate-feeding species),[11] barnacles (e.g. Onchidoris),[12] and anemones (e.g. the Aeolidiidae and other Cladobranchia).[9]

The surface dwelling nudibranch, Glaucus atlanticus is a specialist predator of siphonophores, such as the Portuguese Man O' War. This predatory mollusk sucks air into its stomach to keep it afloat and using its muscular foot it clings to the surface film. If it finds a small victim Glaucus simply envelops it with its capacious mouth, but if the prey is a larger siphonophore the mollusk nibbles off its fishing tentacles, the ones carrying the most potent nematocysts. Like some others of its kind Glaucus does not digest the nematocysts; instead, it uses them to defend itself by passing them from its gut to the surface of its skin.[13]

For a comprehensive list of nudibranch feeding preferences, see the electronic supplement from [14]

Defense mechanisms

Nudibranchs (Nembrotha kubaryana) eating clavelina tunicate colonies. They also take the stinging cells from jellyfish when they eat them.

This group includes some of the most colorful creatures on earth. In the course of evolution, sea slugs have lost their shell because they have developed other defense mechanisms. Some species evolved an external anatomy with textures and colors that mimicked surrounding plants to avoid predators (see camouflage). Other nudibranchs, as seen especially well on chromodorids, have an intensely bright and contrasting color pattern that makes them especially conspicuous in their surroundings. This is believed to be an example of aposematic coloration; the shocking coloration warns potential predators that the slugs are distasteful or poisonous. Evolutionarily, aposematic coloring does not make sense: a bright, conspicuous novel color form would likely be prone to attack before having the chance to reproduce. One explanation for this apparent paradox is the idea of dietary conservatism in predators. This behavior, which involves avoidance of novel food sources, has been shown in many species of predatory birds, with some examples so strong that birds will starve before eating an unfamiliar prey.[15]

Nudibranchs that feed on hydroids can store the hydroids' nematocysts (stinging cells) in the dorsal body wall, the cerata.[16] These stolen nematocysts, called kleptocnidae, wander through the alimentary tract without harming the nudibranch. Once further into the organ, the cells are brought to specific placements on the creature's hind body via intestinal protuberances. Nudibranchs can protect themselves from the hydroids and their nematocysts. It is not yet clear how, but special cells with large vacuoles probably play an important role. They can also take in plants' chloroplasts (plant cell organelles used for photosynthesis) and use them to make food for themselves.

Nudibranchs use a variety of chemical defenses to aid in protection, but it is not necessary for the strategy to be lethal in order to be effective: some successful toxins induce bradycardia or hypotension in a predator, allowing the nudibranch to escape consumption while its attacker is incapacitated.[17] Some sponge-eating nudibranchs concentrate the toxins from their prey sponge in their bodies, rendering themselves toxic to predators.[18] The evidence that suggests the toxins used by dorid nudibranchs do in fact come from dietary sponges lies in the similarities between the primary and secondary metabolites of prey and nudibranchs, respectively. Furthermore, nudibranchs contain a mixture of sponge chemicals when they are in the presence of multiple food sources as well as change defense chemicals with a concurrent change in diet.[19] This, however, is not the only way for nudibranchs to develop chemical defenses. Certain species are able to produce their own chemicals de novo without dietary influence. Evidence for the different methods of chemical production comes with the characteristic uniformity of chemical composition across drastically different environments and geographic locations found throughout de novo production species compared to the wide variety of dietary and environmentally dependent chemical composition in sequestering species.[20]

Another method of protection is the release of an acid from the skin.[21] Once the specimen is physically irritated or touched by another creature, it will release the mucus automatically.


In the past, many taxonomists treated the Nudibranchia as an order, based on the work of Johannes Thiele (1931), who built on the concepts of Henri Milne-Edwards (1848).

Newer insights derived from morphological data and gene-sequence research, seemed to confirm those ideas. On the basis of investigation of 18S rDNA sequence data, there is strong evidence for support of the monophyly of the Nudibranchia and its two major groups, the Anthobranchia/Doridoidea and Cladobranchia.[22] A study published in May 2001, again revised the taxonomy of the Nudibranchia.[23] They were 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 body, 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.

However, according to the taxonomy by Bouchet & Rocroi (2005), currently the most up-to-date system of classifying the gastropods, the Nudibranchia are a subclade within the clade of the Nudipleura. The Nudibranchia are then divided into two clades :

  • Clade Euctenidiacea (= Holohepatica)
  • Clade Nudibranchia Dexiarchia (= Actenidiacea)


  1. ^ Longman Pronunciation Dictionary (2nd edition), ISBN 0582364671
  2. ^ Thompson, T. E. (2009). "Feeding in nudibranch larvae". Journal of the Marine Biological Association of the United Kingdom 38: 239. doi:10.1017/S0025315400006044.  edit
  3. ^
  4. ^ CHASE, RONALD (June 1, 1974). "The Electrophysiology of Photoreceptors in the Nudibranch Mollusc, Tritonia Diomedia". Journal of experimental biology 60 (3): 707–19. PMID 4847278. 
  5. ^ Dayrat, B. (2005). "Advantages of naming species under the PhyloCode: An example of how a new species of Discodorididae (Mollusca, Gastropoda, Euthyneura, Nudibranchia, Doridina) may be named" (PDF). Marine Biology Research 1 (3): 216–232. doi:10.1080/17451000510019141. Retrieved 2009-06-14. 
  6. ^ a b
  7. ^ 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. doi:10.1078/0044-5231-00011. 
  8. ^ NC Folino (1997). "The role of prey mobility in the population ecology of the nudibranch Cuthona nana (Gastropoda: Opisthobranchia)". American Malacological Bulletin. 
  9. ^ a b Domínguez, M.; Troncoso, J. S.; García, F. J. (2008). "The family Aeolidiidae Gray, 1827 (Gastropoda Opisthobranchia) from Brazil, with a description of a new species belonging to the genus Berghia Trinchese, 1877". Zoological Journal of the Linnean Society 153 (2): 349–368. doi:10.1111/j.1096-3642.2008.00390.x.  edit
  10. ^ Rudman, W.B., (1999 (March 19)). "Favorinus tsuruganus Baba & Abe, 1964. [In Sea Slug Forum. Australian Museum"]. 
  11. ^ a b Valdés, �.�N. (2004). "Phylogeography and phyloecology of dorid nudibranchs (Mollusca, Gastropoda)". Biological Journal of the Linnean Society 83 (4): 551–559. doi:10.1111/j.1095-8312.2004.00413.x.  edit
  12. ^ Barnes, H.; Powell, H. T. (1954). "Onchidoris fusca (Müller); A Predator of Barnacles". Journal of Animal Ecology 23 (2): 361–363. doi:10.2307/1986. JSTOR 1986.  edit
  13. ^ Piper, Ross (2007), Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals, Greenwood Press.
  14. ^ MCDONALD, G. R., & J. W. NYBAKKEN. 1997. A worldwide review of the food of nudibranch mollusks. I. Introduction and the suborder Arminacea. Veliger 40(2): 157-159. MCDONALD, G. R., & J. W. NYBAKKEN. 1999. A worldwide review of the food of nudibranch mollusks. II. The suborder Dendronotacea. Veliger 42(1): 62-66.. 
  15. ^ Marples, N. M., D. J. Kelly, and R. J. Thomas. 2005. Perspective: The evolution of warning coloration is not paradoxical. Evolution 59:933-940
  16. ^ Frick, K (2003). "Predator Suites and Flabellinid Nudibranch Nematocyst Complements in the Gulf of Maine". In: SF Norton (ed). Diving for Science...2003. Proceedings of the American Academy of Underwater Sciences (22nd Annual Scientific Diving Symposium). Retrieved 2008-07-03. 
  17. ^ Fuhrman, F. A., G. J. Fuhrman, and K. Deriemer. 1979. Toxicity and pharmacology of extracts from dorid nudibranchs. Biological Bulletin 156:289-299
  18. ^ Gosliner, T.M. 1987. Nudibranchs of Southern Africa ISBN 0-930118-13-8
  19. ^ Faulkner, D. J., and M. T. Ghiselin. 1983. Chemical defense and evolutionary ecology of dorid nudibranchs and some other opisthobranch gastropods. Marine Ecology-Progress Series 13:295-301.
  20. ^ Barsby, T., R. G. Linington, and R. J. Andersen. 2002. De Novo terpenoid biosynthesis by the dendronotid nudibranch Melibe leonina. Chemoecology 12:199-202
  21. ^ Edmunds, M. 1968. Acid secretion in some species of Doridacea (Mollusca, Nudibranchia). Proceedings of the Malacological Society of London 38:121-133
  22. ^ Wägele H. & Willan R. C. (September 2000). "Phylogeny of the Nudibranchia". Zoological Journal of the Linnean Society 1 (1): 83–181. doi:10.1111/j.1096-3642.2000.tb02196.x. 
  23. ^ Schrödl M., Wägele H. & 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. doi:10.1078/0044-5231-00008. 

Further reading

  • Gary R. McDonald. July 29, 2006. Nudibranch Systematic Index. Institute of Marine Sciences. Paper Nudibranch_Systematic_Index. - Note: This is a good resource for getting a species list in certain genera, but it is not good for ascertaining the taxonomy of a genera, because it does not use the taxonomy of the Gastropoda (Bouchet & Rocroi, 2005).
  • Neville Coleman (2008). Nudibranchs Encyclopedia: Catalogue of Asia/Indo-Pacific Sea Slugs. Neville Coleman's Underwater Geographic. ISBN 0947325417

External links


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Look at other dictionaries:

  • Nudibranch — Nu di*branch, a. (Zo[ o]l.) Of or pertaining to the Nudibranchiata. n. One of the Nudibranchiata. [1913 Webster] …   The Collaborative International Dictionary of English

  • nudibranch — [no͞o′dibraŋk΄, no͞o′dəbraŋk΄, nyo͞o′dibraŋk΄, nyo͞o′dəbraŋk΄] n. [< ModL Nudibranchia: see NUDI & BRANCHIAE] any of an order (Nudibranchia) of marine gastropods without a shell and with external gills nudibranchiate [no͞o′dibraŋ′kē it,… …   English World dictionary

  • nudibranch — noun (plural branchs) Etymology: New Latin Nudibranchia, from Latin nudus + Greek branchia gills Date: 1844 any of an order (Nudibranchia) of marine opisthobranch mollusks without a shell in the adult state and without true gills • nudibranch… …   New Collegiate Dictionary

  • nudibranch — /nooh deuh brangk , nyooh /, n. a shell less, marine snail of the suborder Nudibranchia, having external, often branched respiratory appendages on the back and sides. [1835 45; < F nudibranche, equiv. to nudi NUDI + branche gill ( < L branchia… …   Universalium

  • nudibranch — noun /njuːdɪbræŋk/ A term for any sea slug; specifically the animals belonging to the suborder Nudibranchia, the largest suborder of the order Opisthobranchia …   Wiktionary

  • nudibranch — [ nju:dɪbraŋk] noun Zoology a shell less marine mollusc of the order Nudibranchia; a sea slug. Origin from mod. L. Nudibranchia, from L. nudus nude + branchia …   English new terms dictionary

  • nudibranch — nu·di·branch …   English syllables

  • nudibranch — nu•di•branch [[t]ˈnu dəˌbræŋk, ˈnyu [/t]] n. ivt any shell less marine gastropod mollusk of the suborder Nudibranchia, having external, often branched respiratory appendages • Etymology: 1835–45 …   From formal English to slang

  • nudibranch — /ˈnjudəbræŋk/ (say nyoohduhbrangk) noun a shell less type of marine snail with external respiratory appendages, noted for its beautiful colouring and graceful form. {French nudibranche, from nudi nudi + branche gills, from Latin branchia… …  

  • nudibranch — noun any of various marine gastropods of the suborder Nudibranchia having a shell less and often beautifully colored body • Syn: ↑sea slug • Hypernyms: ↑gastropod, ↑univalve • Hyponyms: ↑Hermissenda crassicornis • …   Useful english dictionary

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