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The radula (US: / ˈ r æ dʒ ʊ l ə /; pl.: radulae or radulas) [1] is an anatomical structure used by mollusks for feeding, sometimes compared to a tongue. [2] It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food enters the esophagus .
The buccal mass is the first part of the digestive system, and consists of the mouth and pharynx. The mouth includes a radula, and in most cases, also a pair of jaws. The pharynx can be very large, especially in carnivorous species. Many carnivorous species have developed a proboscis, containing the oral cavity, radula, and part of the ...
The radula is more similar to coleoids, with 9 elements per row, than to the nautilus, with 13 elements per row. Ammonoids have been found with coleoid-like radulas, as have orthoconic nautiloids dating back to the Ordovician Period (Gabbott, 1999).
Muscles that control the radula are shown in brown. The surface of the radula ribbon, with numerous teeth, is shown as a zig-zag line. The odontophore is part of the feeding mechanism in molluscs. It is the cartilage which underlies and supports the radula, a ribbon of teeth. [1] The radula is found in every class of molluscs except for the ...
In most cephalopods, such as octopus, squid, and cuttlefish, the hyponome is a muscular tube. The hyponome of the nautilus differs however, in that it is a one-piece flap that is folded over. Whether ammonites possessed a hyponome and if so what form it may have taken, is as yet not known.
[3] 80% of solenogaster species have a radula, while in others it is secondarily lost. The radula may bear one or more teeth per row; where there is more than one tooth, there is no central radular tooth. [3] The radula grows by dividing existing teeth in two, or by adding a new tooth at the center of the radular row. [3]
In a broad sense, "nautiloid" refers to a major cephalopod subclass or collection of subclasses (Nautiloidea sensu lato). Nautiloids are typically considered one of three main groups of cephalopods, along with the extinct ammonoids (ammonites) and living coleoids (such as squid, octopus, and kin).
Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and Spirula. In the case of the cuttlefish, the siphuncle is indistinct and connects all the small chambers of that animal's highly modified shell; in the other cephalopods it is thread-like and passes ...