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41-535: See text for superfamilies Nudibranchs ( / ˈ nj uː d ɪ b r æ ŋ k / ) belong to the order Nudibranchia , a group of soft-bodied marine gastropod molluscs that shed their shells after their larval stage. They are noted for their often extraordinary colours and striking forms, and they have been given colourful nicknames to match, such as "clown", "marigold", "splendid", "dancer", "dragon", and "sea rabbit". Currently, about 3,000 valid species of nudibranchs are known. The word nudibranch comes from

82-401: A coiled shell, but the shell is shed at metamorphosis when the larva transforms into the adult form. Some species have direct development , and the shell is shed before the animal emerges from the egg mass. 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. By contrast, on

123-414: A few minutes, and involves a dance-like courtship. Nudibranchs typically deposit their eggs within a gelatinous spiral, which is often described as looking like a ribbon. The number of eggs varies; it can be as few as just 1 or 2 eggs ( Vayssierea felis ) or as many as an estimated 25 million ( Aplysia fasciata ). The eggs contain toxins from sea sponges as a means of deterring predators. After hatching,

164-494: A month, and during the whole period of their confinement they have continued to produce the sounds with very little diminution of their original intensity. In a small apartment they are audible at the distance of twelve feet. The sounds obviously proceed from the mouth of the animal; and at the instant of the stroke, we observe the lips suddenly separate, as if to allow the water to rush into a small vacuum formed within. As these animals are hermaphrodites, requiring mutual impregnation,

205-519: A particular order should be recognized at all. Often there is no exact agreement, with different taxonomists each taking a different position. There are no hard rules that a taxonomist needs to follow in describing or recognizing an order. Some taxa are accepted almost universally, while others are recognized only rarely. The name of an order is usually written with a capital letter. For some groups of organisms, their orders may follow consistent naming schemes . Orders of plants , fungi , and algae use

246-406: A quarter of a millimeter in diameter, and consist of a lens and five photoreceptors. Nudibranchs vary in adult size from 4 to 600 mm (0.16 to 23.62 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). In most species, there is a swimming veliger larva with

287-423: A topic of recent revision. Traditionally, nudibranchs have been treated as the order Nudibranchia, located in the gastropod mollusc subclass Opisthobranchia (the marine slugs: which consisted of nudibranchs, sidegill slugs , bubble snails , algae sap-sucking sea slugs, and sea hares ). Since 2005, pleurobranchs (which had previously been grouped among sidegill slugs) have been placed alongside nudibranchs in

328-548: A variety of chemical defences to aid in protection, but the strategy need not be lethal to be effective; in fact, good arguments exist that chemical defences should evolve to be distasteful rather than toxic. Some sponge-eating nudibranchs concentrate the chemical defences from their prey sponge in their bodies, rendering themselves distasteful to predators. One method of chemical defense used by nudibranchs are secondary metabolites, which play an important role in mediating relationships among marine communities. The evidence that suggests

369-519: Is longest and most often repeated when the Tritonia are lively and moving about, and is not heard when they are cold and without any motion; in the dark I have not observed any light emitted at the time of the stroke; no globule of air escapes to the surface of the water, nor is any ripple produced on the surface at the instant of the stroke; the sound, when in a glass vessel, is mellow and distinct.' The Professor has kept these Tritonia alive in his room for

410-471: Is seen in warm, shallow reefs, although one nudibranch species was discovered at a depth near 2,500 m (8,200 ft). This nudibranch, described in 2024 as Bathydevius , is the only known nudibranch with a bathypelagic lifestyle and is one of the very few to be bioluminescent . Nudibranchs are benthic animals, found crawling over the substrate. The only exceptions to this are the neustonic Glaucus nudibranchs, which float upside down just under

451-590: Is yet unknown, but special cells with large vacuoles probably play an important role. Similarly, some nudibranchs can also take in plant cells (symbiotic algae from soft corals) and reuse these to make food for themselves. The related group of sacoglossan sea slugs feed on algae and retain just the chloroplasts for their own photosynthetic use, a process known as kleptoplasty . Some of these species have been observed practicing autotomy , severing portions of their body in order to remove parasites, and have been observed to regrow their head if decapitated. Nudibranchs use

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492-628: The Prodromus Systematis Naturalis Regni Vegetabilis of Augustin Pyramus de Candolle and the Genera Plantarum of Bentham & Hooker, it indicated taxa that are now given the rank of family (see ordo naturalis , ' natural order '). In French botanical publications, from Michel Adanson 's Familles naturelles des plantes (1763) and until the end of the 19th century, the word famille (plural: familles )

533-510: The Aeolidiidae and other Cladobranchia ). The surface-dwelling nudibranch, Glaucus atlanticus , is a specialist predator of siphonophores , such as the Portuguese man o' war . This predatory mollusc 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

574-527: The Latin nudus 'naked' and the Ancient Greek βράγχια ( bránkhia ) ' gills '. Nudibranchs are often casually called sea slugs , as they are a family of opisthobranchs (sea slugs), within the phylum Mollusca (molluscs), but many sea slugs belong to several taxonomic groups that are not closely related to nudibranchs. A number of these other sea slugs, such as the photosynthetic Sacoglossa and

615-408: The dorsal body wall, the cerata . These stolen nematocysts, called kleptocnidae , wander through the alimentary tract without harming the nudibranch. Once further into the organ, the cells are assimilated by intestinal protuberances and brought to specific placements on the creature's hind body. The specific mechanism by which nudibranchs protect themselves from the hydrozoids and their nematocysts

656-802: The back of the aeolids in the clade Cladobranchia , brightly coloured sets of protruding organs called cerata are present. Nudibranchs have cephalic (head) tentacles, which are sensitive to touch, taste, and smell. Club-shaped rhinophores detect odors. In the course of their evolution, nudibranchs have lost their shells, while developing alternative defence mechanisms. Some species evolved an external anatomy with textures and colours that mimicked surrounding sessile invertebrate animals (often their prey sponges or soft corals) to avoid predators with camouflage . Other nudibranchs, as seen especially well on Chromodoris quadricolor , have an intensely bright and contrasting colour pattern that makes them especially conspicuous in their surroundings. Nudibranch molluscs are

697-604: The basis of investigation of 18S rDNA sequence data, strong evidence supports the monophyly of the Nudibranchia and its two major groups, the Anthobranchia/Doridoidea and Cladobranchia. A study published in May 2001, again revised the taxonomy of the Nudibranchia. They were thus divided into two major clades: However, according to the taxonomy by Bouchet & Rocroi (2005) , currently the most up-to-date system of classifying

738-762: The chemical compounds used by dorid nudibranchs do in fact come from dietary sponges lies in the similarities between the 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 defence chemicals with a concurrent change in diet. This, however, is not the only way for nudibranchs to develop chemical defences. Certain Antarctic marine species defense mechanisms are believed to be controlled by biological factors like predation and competition, and selective pressures. Certain species are able to produce their own chemicals de novo without dietary influence. Evidence for

779-404: The clade Nudipleura (recognising them as more closely related to each other than to other opisthobranchs). Since 2010 , Opisthobranchia has been recognised as not a valid clade (it is paraphyletic ) and instead Nudipleura has been placed as the first offshoot of Euthyneura (which is the dominant clade of gastropods). In 2024, a brand new family of deep-sea pelagic nudibranch, Bathydeviidae ,

820-605: The colourful Aglajidae , are often confused with nudibranchs. Nudibranchs occur in seas worldwide, ranging from the Arctic, through temperate and tropical regions, to the Southern Ocean around Antarctica. They are almost entirely restricted to salt water, although a few species are known to inhabit lower salinities in brackish water . Nudibranchs live at virtually all depths, from the intertidal zone to depths well over 700 m (2,300 ft). The greatest diversity of nudibranchs

861-407: 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. Another method of protection is the release of the ugdon acid from

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902-468: The ending -anae that was initiated by Armen Takhtajan 's publications from 1966 onwards. The order as a distinct rank of biological classification having its own distinctive name (and not just called a higher genus ( genus summum )) was first introduced by the German botanist Augustus Quirinus Rivinus in his classification of plants that appeared in a series of treatises in the 1690s. Carl Linnaeus

943-888: The field of zoology , the Linnaean orders were used more consistently. That is, the orders in the zoology part of the Systema Naturae refer to natural groups. Some of his ordinal names are still in use, e.g. Lepidoptera (moths and butterflies) and Diptera (flies, mosquitoes, midges, and gnats). In virology , the International Committee on Taxonomy of Viruses 's virus classification includes fifteen taxomomic ranks to be applied for viruses , viroids and satellite nucleic acids : realm , subrealm , kingdom , subkingdom, phylum , subphylum , class, subclass, order, suborder, family, subfamily , genus, subgenus , and species. There are currently fourteen viral orders, each ending in

984-458: The gastropods, the Nudibranchia are a subclade within the clade of the Nudipleura . The Nudibranchia are then divided into two clades, with a third described in 2024: This gallery shows some of the great variability in the color and form of nudibranchs, and nudibranch egg ribbons. Order (biology) What does and does not belong to each order is determined by a taxonomist , as is whether

1025-785: The infants look almost identical to their adult counterparts, albeit smaller. Infants may also have fewer cerata . The lifespan of nudibranchs can range from a few weeks to a year, depending on the species. All known nudibranchs are carnivorous . Some feed on sponges , others on hydroids (e.g. Cuthona ), others on bryozoans ( phanerobranchs such as Tambja , Limacia, Plocamopherus and Triopha ), and some eat other sea slugs or their eggs (e.g. Favorinus ) or, on some occasions, are cannibals and prey on members of their own species. Other groups feed on tunicates (e.g. Nembrotha , Goniodoris ), other nudibranchs ( Roboastra , which are descended from tunicate-feeding species), barnacles (e.g. Onchidoris bilamellata ), and anemones (e.g.

1066-430: The interesting fact in some specimens of the latter which he was keeping in an aquarium, says of the sounds, that 'they resemble very much the clink of a steel wire on the side of the jar, one stroke only been given at a time, and repeated at intervals of a minute or two; when placed in a large basin of water the sound is much obscured, and is like that of a watch, one stroke being repeated, as before, at intervals. The sound

1107-400: The largest of tropical marine slugs, potently chemically defended, and brilliantly red and white, is nocturnal and has no known mimics. Other studies of nudibranch molluscs have concluded they are aposematically coloured, for example, the slugs of the family Phylidiidae from Indo-Pacific coral reefs. Nudibranchs that feed on hydrozoids can store the hydrozoids' nematocysts (stinging cells) in

1148-446: The latest classification. A morphological phylogenetic study, published in 2000, by Wägele & Willan showed that the subclade Gnathodoridacea (= Bathydoridoidea) and the subclade Doridacea (= Phanerobranchia + Cryptobranchia + Porostomata) each form a monophyletic group. In a later study, published in 2002, A. Valdés concluded that the superfamilies Doridoidea and Phyllidioidea (called by him Cryptobranchia + Porostomata) formed

1189-415: The male and female sexual openings are on the right side of the body, reflecting their asymmetrical origins. They lack a mantle cavity. Some species have venomous appendages ( cerata ) on their sides, which deter predators. Many also have a simple gut and a mouth with a radula . The eyes in nudibranchs are simple and able to discern little more than light and dark. The eyes are set into the body, are about

1230-449: The most commonly cited examples of aposematism in marine ecosystems, but the evidence for this has been contested, mostly because few examples of mimicry are seen among species, many species are nocturnal or cryptic, and bright colours at the red end of the spectrum are rapidly attenuated as a function of water depth. For example, the Spanish dancer nudibranch (genus Hexabranchus ), among

1271-470: The ocean's surface; the pelagic nudibranchs Cephalopyge trematoides , which swim in the water column; the two pelagic species of Phylliroe , and the evolutionarily distinct, bathypelagic Bathydevius . The body forms of nudibranchs vary greatly. Because they are opisthobranchs, unlike most other gastropods, they are apparently bilaterally symmetrical externally (but not internally) because they have undergone secondary detorsion . In all nudibranchs,

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1312-449: The prey is a larger siphonophore, the mollusc 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. Nudibranchs are commonly divided into two main kinds, dorid and aeolid (also spelled eolid) nudibranchs: The exact systematics of nudibranchs are

1353-420: The same position. Michael Benton (2005) inserted them between superorder and magnorder instead. This position was adopted by Systema Naturae 2000 and others. In botany , the ranks of subclass and suborder are secondary ranks pre-defined as respectively above and below the rank of order. Any number of further ranks can be used as long as they are clearly defined. The superorder rank is commonly used, with

1394-571: The skin. Once the specimen is physically irritated or touched by another creature, it will release the mucus automatically, eating the animal from the inside out. In 1884, Philip Henry Gosse reported observations by "Professor Grant" (possibly Robert Edmond Grant ) that two species of nudibranchs emit sounds that are audible to humans. Two very elegant species of Sea-slug, viz., Eolis punctata [i.e. Facelina annulicornis ], and Tritonia arborescens [i.e. Dendronotus frondosus ], certainly produce audible sounds. Professor Grant, who first observed

1435-399: The sounds may possibly be a means of communication between them, or, if they are of an electric nature, they may be the means of defending from foreign enemies one of the most delicate, defenceless, and beautiful Gasteropods that inhabit the deep. Nudibranchs are hermaphroditic , thus having a set of reproductive organs for both sexes, but they cannot fertilize themselves. Mating usually takes

1476-765: The suffix -ales (e.g. Dictyotales ). Orders of birds and fishes use the Latin suffix -iformes meaning 'having the form of' (e.g. Passeriformes ), but orders of mammals and invertebrates are not so consistent (e.g. Artiodactyla , Actiniaria , Primates ). For some clades covered by the International Code of Zoological Nomenclature , several additional classifications are sometimes used, although not all of these are officially recognized. In their 1997 classification of mammals , McKenna and Bell used two extra levels between superorder and order: grandorder and mirorder . Michael Novacek (1986) inserted them at

1517-415: The suffix -virales . Anthobranchia The Doridina , common name dorid nudibranchs , are a taxonomic suborder of sea snails or slugs , marine gastropod molluscs in the order Nudibranchia . Bouchet & Rocroi (2005) rejected the name Anthobranchia on the grounds that it also included Onchidium at the time of original publication. Doridina is equivalent and used in

1558-574: The word family ( familia ) was assigned to the rank indicated by the French famille , while order ( ordo ) was reserved for a higher rank, for what in the 19th century had often been named a cohors (plural cohortes ). Some of the plant families still retain the names of Linnaean "natural orders" or even the names of pre-Linnaean natural groups recognized by Linnaeus as orders in his natural classification (e.g. Palmae or Labiatae ). Such names are known as descriptive family names. In

1599-461: Was described containing a single genus, Bathydevius . This family does not appear to be closely related to any other extant nudibranch, and is the only known bathypelagic nudibranch taxon. This classification was based on the work of Johannes Thiele (1931), who built on the concepts of Henri Milne-Edwards (1848). Order Nudibranchia: Newer insights derived from morphological data and gene-sequence research seemed to confirm those ideas. On

1640-543: Was the first to apply it consistently to the division of all three kingdoms of nature (then minerals , plants , and animals ) in his Systema Naturae (1735, 1st. Ed.). For plants, Linnaeus' orders in the Systema Naturae and the Species Plantarum were strictly artificial, introduced to subdivide the artificial classes into more comprehensible smaller groups. When the word ordo was first consistently used for natural units of plants, in 19th-century works such as

1681-540: Was used as a French equivalent for this Latin ordo . This equivalence was explicitly stated in the Alphonse Pyramus de Candolle 's Lois de la nomenclature botanique (1868), the precursor of the currently used International Code of Nomenclature for algae, fungi, and plants . In the first international Rules of botanical nomenclature from the International Botanical Congress of 1905,

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