The Gastropod Radula

GASTROPODA (stem group)
|--PARAGASTROPODA  
`--+--TERGOMYA (paraphyletic)
   `--Gastropoda (crown group)  
      |--EOGASTROPODA  
      |  |--Macluritoidea
      |  `--PATELLOGASTROPODA
      `--ORTHOGASTROPODA  
         |--NERITOPSINA
         |  |--Neritoida
         |  `--VETIGASTROPODA
         `--Apogastropoda

Description of Radula Types

The following description is taken from Lindner 1975 pp.21-22, (I have added some comments in brackets) and constitute a rough evolutionary sequence (apart from the Ptenoglossan condition which represents a specialized side-branch):

"In the docoglossan radula [4] above, there is one usually small central tooth, flanked by 1-3 laterals and a few (3 at the most) hooked marginals. (This is the most primitive radula type, and we could assume it represents the plesiomorphic condition, such as would be possessed by the first molluscs (Eogastropoda, also Polyplacophora [7]))

In the rhipidoglossan radula, [5] there is a large central tooth, flanked on each side by five laterals and numerous closely packed marginals (the rhipidoglossan radula marks an improvement over the primitive docoglossan type with a greater number of small side-teeth [Vetigastropoda, Neritomorpha]).

In the taenioglossan radula ([1], [3], [6], above), the central tooth is flanked on each side by one lateral and two marginal teeth (characteristic of the majority of Mesogastropoda);

In the ptenoglossan radula has no central tooth but a series of several uniform, pointed teeth (Epitoniodea)

In the stenoglossan or rachiglossan radula [2], has one central tooth and one lateral tooth on each side (most Neogastropoda)

in the toxoglossan radula [8] each row has only two teeth of which only one is in use at a time. These teeth are very long and pointed, with venom channels and barbs, and are not firmly fixed to the basal plate. The teeth can therefore be individually transferred to the proboscis and ejected into the prey as a sting (Conoidea)."