page_title: Nudibranch
section_title: Anatomical description
hierarchical_section_title: Nudibranch / Anatomical description
caption_attribution_description: English: Photo of dorsal view of mature of Berghia stephanieae (Valdés, 2005) (synonym:Aeolidiella stephanieae}. Scale bar is 100 μm. ot = oral tentacles, ft = foot tentacles e = eye, r = rhinophores, cn =cnidosacs at the cerata tips. c = cerata.
context_page_description: Nudibranchs are a group of soft-bodied, marine gastropod molluscs which 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," or "sea rabbit." Currently, about 3,000 valid species of nudibranchs are known.
  The word "nudibranch" comes from the Latin nudus "naked" and the Ancient Greek βράγχια "gills".
  Nudibranchs are often casually called sea slugs, as they are a family of opistobranchs, within the phylum Mollusca, but many sea slugs belong to several taxonomic groups which are not closely related to nudibranchs. A number of these other sea slugs, such as the photosynthetic Sacoglossa and the colourful Aglajidae, are often confused with nudibranchs.
context_section_description: The body forms of nudibranchs vary a great deal, but 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, 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 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(in shelled gastropods, the operculum is a bony or horny plate that can cover the opening of the shell when the body is withdrawn).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 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 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.
caption: Berghia stephanieae  nudibranch body: Note the oral tentacles (ot), foot tentacles (ft), eye (e), rhinophores (r), and cerata (c). This species has cnidosacs (cn) at the cerata tips. Scale bar is 100 μm.
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