230 



RADULA OF OPISTHOBRANCHIATA 



CHAP. 



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

 Dotoidae, Hermaeidae, Elysiidae (Fig. 135), and Limapontiidae. 

 In the Aeolididae it is sometimes accompanied by a single 

 lateraL The same type occurs in Oxynoe^ and in Lohiger ( = 

 Lophocercus). 



(5) Radula 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^ Scaphander (Fig. 137, A), Philine 

 (certain species), Ringicula^ or (2) first lateral strongly devel- 

 oped, and repeated in succeeding laterals (2-6) on a smaller 

 scale, e.g. Pliilwe (certain species). A few marginals are some- 



FiG. 135. — Radula of Elysia 

 viridis Mont, x 40. Type 



(a). 



Fig. 136. — Portion of the radula 

 of Gadinia peruviana Sowb., 

 Chili. x250. Type (c). 



times added, e.g. in Polycera, Lamellidoris (where there is a 

 degraded central tooth. Fig. 137, B), Idalia^ and Aneula. 



(c~) Radula 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 Doris (e.g. Ohromodorisy Aphelodoris, Oasella^ Centrodoris)., of 

 Hypohranchiaea and Pleurophyllidia ; among the Tectibranchiata, 

 of Actaeon, many of the Bullidae, Aplustrum, the Aplysiidae, 

 Pleurohranchus, Umbrella and Gradinia (Figs. 136 and 137, C). 



In the Pteropoda there are two types of radula. The Gym- 

 nosomata, which are in the main carnivorous, possess a radula 

 with a varying number (4-12) of sickle-shaped marginals, cen- 

 tral 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 base. 



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