230 



RADULA OF OPISTHOBRANCHIATA 



This form is characteristic of the Aeolididae, Fionidae, Glaucidae, 

 Dotoidae, Herinaeidae, Elysiidae (Fig. 135), and Liinapontiidae. 

 In the Aeolididae it is sometimes accompanied by a single 

 lateral. The same type occurs in Oxynoe, and in Lohigcr ( = 

 Lo;p]iocercus). 



(h) Eadula with the first lateral very strongly developed. 

 This type may take the form of ( 1 ) a single lateral, no central or 

 marginals, e.g. Onchidoris, Scajjhander (Fig. 137, A) Philine 

 (certain species), Binginda, or (2) first lateral strongly developed, 

 and repeated in succeeding laterals (2-6) on a smaller scale, e.g. 

 Philine (certain species). A few marginals are sometimes added, 



Fig. 135.— Eadula of Elysia 

 viridis Mont. x 40. Type 



Fig. 136.— Portion of the radula 

 of Gadinia 2}eruviana Sowb., 

 Chili. X 250. Type (c). 



e.g. in Polycera, Lamellidoris (where there is a degraded central 

 tooth, Fig. 137, B), Idcdia, and Aiicula. 



(c) Eadula with an indefinite number of marginals, laterals 

 (if present) merging into marginals, central tooth present or 

 absent, inconspicuous, teeth all very small. This type of radula, 

 among the Nudibranchiata, is characteristic of certain subgenera 

 of If oris (e.g. Chromodoris, Aphelodoris, Casella, Ccntrodoris), of 

 Hypobrancliiaca and Pleuro2^hyUidia ; among the Tectibranchiata, 

 of Actaeon, many of the BuUidae, Axjlustruin, the Aplysiidae, 

 PUurobranclius, Umbrella and Gadinia (Figs. 136 and 137, C). 



In the Pterojioda there are two types of radula. The Gymno- 

 somata, which are in the main carnivorous, possess a radula wath a 

 varying number (4-12) of sickle-shaped marginals, central tooth 

 present or absent. In the Thecosomata, which feed on a vegetable 

 diet, there are never more than three teeth, a central and a 

 marginal on each side ; teeth more or less cusped on a square Ijase. 



