A rhinophore is one of a pair of club-shaped structures which are the most prominent part of the external head anatomy of a group of sea slugs, marine gastropod opisthobranch mollusks in the order Nudibranchia, the nudibranchs, specifically the dorid nudibranchs.
The name relates to the rhinophore's function as an organ of "smell". "Rhino-" means nose from Ancient Greek ῥίς rhis and from its genitive ῥινός rhinos. "Phore" means "to bear" from New Latin -phorus and from Greek -phoros (φορος) "bearing", a derivative of phérein (φέρειν).
Rhinophores are specialized anterior sensory organs on the dorsal surface of the head. Rhinophores are retractile and primarily used for distance chemoreception and rheoreception (response to water current).
The "scents" detected by rhinophores are chemicals dissolved in the sea water. The fine structure and hairs of the rhinophore provide a large surface area so that chemical detection is maximized. This allows the nudibranchs to stay close to their food source (for example species of sea sponges) which are also the living substrate they preferentially inhabit.
To protect the prominent rhinophores against nibbling by predators including fish, most species of dorid nudibranchs are able to withdraw their rhinophores into a pocket beneath the skin.
Rhinophores are small. For example in reproductively mature Aplysia adults the rhinophore is about 1 cm in length.
The neuroanatomical organization of rhinophores includes a rhinophore groove where most of the sensory cells appear to be concentrated. Its sensory epithelium contains sensory neurons that project axons back to rhinophore ganglia and dendrites that end in either a surface-exposed cilium or a small protuberance.
Comparison with oral tentacles
In Aplysia californica, the oral tentacles, which are situated in a more ventral position, are possibly involved in contact chemoreception and mechanoreception.
- Scott F Cummins, Dirk Erpenbeck, Zhihua Zou, Charles Claudianos, Leonid L Moroz, Gregg T Nagle & Bernard M Degnan. 2009. Candidate chemoreceptor subfamilies differentially expressed in the chemosensory organs of the mollusc Aplysia. BMC Biology 2009, 7:28. doi:10.1186/1741-7007-7-28.
- Rhinophore in nudibranchs. Sea Slug Forum, accessed 8 July 2009.
- Wertz A., Rössler W., Obermayer M. & Bickmeyer U. (6 April 2006) "Functional neuroanatomy of the rhinophore of Aplysia punctata". Frontiers in Zoology 3: 6. doi:10.1186/1742-9994-3-6
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