234 



THE BIOLOGY OF MARINE ANIMALS 



its supporting cartilage, as over a pulley. Since the radular teeth slope 

 backwards the effective stroke is executed on withdrawal, and this accords 

 with the greater size of the radular retractor. 



In herbivorous chitons and gastropods radular teeth are well developed. 

 Representative browsing forms are Chiton and Patella, which scrape 



Fig. 5.25. Proboscis of a Carnivorous Gastropod Natica millepunctata 

 Radula in mouth opening, boring gland below. (From Ankel (5).) 



encrusting algae and other small organisms off rocks. Pieces of seaweed 

 are also eaten, being seized with lips and palate and scraped with the 

 radula. Aplysia (an opisthobranch) browses on green algae, which are 

 grasped by lips and jaws and rasped by the radula. Eolids feed on hydroids 

 and sea anemones, breaking off pieces with the jaws and passing them back 

 with the radula. They appear to be physiologically specialized in some 

 manner for inactivating the nematocysts of their prey. Many of the dorids 

 browse on sponges, using the radula as rasp and scoop. Others, such as 



