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The sixgill stingray has a bulky, flabby body with a rounded pectoral fin disc that is longer than wide. The triangular snout is much longer in adults than in juveniles (making up almost two-fifths of the disc length), and is filled with a clear gelatinous material; because of this, the snout of a dead specimen can shrink significantly when exposed to air or preservatives.
The oldest known stingray taxon is "Dasyatis" speetonensis from the Hauterivian of England, whose teeth most closely resemble that of the extant sixgill stingray (Hexatrygon). Although stingray teeth are rare on sea bottoms compared to the similar shark teeth, scuba divers searching for the latter do encounter the teeth of stingrays. [6] [8]
The rate of tooth replacement varies from once every 8 to 10 days to several months, although few studies have been able to quantify this. In most species of bony fish , teeth are replaced one at a time as opposed to the simultaneous replacement of an entire row.
Rhinoptera bonasus (Mitchill, 1815) - cownose stingray teeth & skeletal mouthparts (public display, Greater Cleveland Aquarium, Cleveland, Ohio, USA). I've seen fossil stingray teeth several times, but never understood them until now. The aquarium display shown above is the skeletal mouth remains of a modern cownose stingray.
Cownose ray teeth and mouthparts. Stingray teeth consist of interlocking bars (dental plates) that crush food. The cownose ray exhibits a durophagous diet, meaning it feeds upon hard-shelled organisms, such as mollusks , crustaceans , but they prefer scallops or clams , which have softer shells and are categorized as bivalves . [ 2 ]
New, permanent teeth grow in the jaws, usually under or just behind the old tooth, from stem cells in the dental lamina. [5] Young animals typically have a full set of teeth when they hatch; there is no tooth change in the egg. Within days, tooth replacement begins, usually in the back of the jaw continuing forward like a wave.
Batomorphi is a clade of cartilaginous fishes, commonly known as rays, this taxon is also known as the superorder Batoidea, but the 5th edition of Fishes of the World classifies it as the division Batomorphi. [2]
The mouth cone ("everted pharynx") of a possible new species of Meiopriapulus, a marine worm in the Priapulida, bears pharyngeal teeth. [5] Fossils of the Yunnanozoon and Haikouella possess pharyngeal teeth. The lower pharyngeal bones of cichlids also carry specialized teeth which augment their normal mandibular teeth in the breakdown of food.
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