|
    Photography: Kurt Fehr |
Frosted Nudibranch - Dirona albolineata
A nudibranch is a member of one suborder of soft-bodied, shell-less marine opisthobranch gastropod mollusks, which are 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 the Latin nudus, naked, and the Greek brankhia, gills. Nudibranchs are often casually called "sea slugs", a non-scientific term. This has led some people to assume that every sea slug must be a nudibranch. Nudibranchs are very numerous in terms of species, and are often very attractive and noticeable, but there are a wide variety of other kinds of sea slugs, and these belong to several taxonomic groups that are not very closely related to nudibranchs. A fair number of these other sea slugs are colorful, and can be confused with nudibranchs. These other marine shell-less gastropods or "sea slug" groups include additional heterobranch shell-less gastropod groups such as the Cephalaspidea sea slugs including the colorful Aglajidae, and other heterobranchs such as the Sacoglossa, the sea butterflies, the sea angels, and the often rather large sea hares. The term sea slug is also sometimes loosely applied to the only very distantly related, pelagic, caenogastropods within the superfamily Carinarioidea, and may also be casually used for the even more distantly related pulmonate sea slugs, the Onchidiidae. 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. 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adult form is without a shell or operculum (a bony or horny plate covering the opening of the shell, when the body is withdrawn).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 odors. |
|