Odontodes, or dermal teeth, are hard structures found on the external surfaces of animals or near internal openings. They comprise a soft pulp surrounded by dentine and covered by a mineralized substance such as enamel

Tooth enamel

Tooth enamel, along with dentin, cementum, and dental pulp is one of the four major tissues that make up the tooth in vertebrates. It is the hardest and most highly mineralized substance in the human body. Tooth enamel is also found in the dermal denticles of sharks...

, a structure similar to that of teeth

Tooth

Teeth are small, calcified, whitish structures found in the jaws of many vertebrates that are used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth are embedded in the Mandible bone or the Maxillary bone and are...

. They generally do not have the same function as teeth, and are not replaced the same way teeth are in most fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

. In some animals (notably catfish) the presence or size of odontodes can be used in determining the sex.

The name comes from the Greek "odon" meaning tooth; a similarly named subject are the Class of animals known as Conodont

Conodont

Conodonts are extinct chordates resembling eels, classified in the class Conodonta. For many years, they were known only from tooth-like microfossils now called conodont elements, found in isolation. Knowledge about soft tissues remains relatively sparse to this day...

s ("cone teeth"), which were first known from their fossilised primitive teeth. http://www.em-consulte.com/article/189295/auto

Images

A New Species of Hisonotus (Siluriformes,Loricariidae) of the Upper Rı´o Uruguay Basin (see page 7) An article showing scanning electron microscope images of odontodes on a catfish. Author:Adriana E. Aquino, Scott A. Schaefer, Amalia M. Miquelarena. Publisher: The American Museum of Natural History.