170 



ZOOLOGY 



ve 



sh 



ward, close to the rock or another shell. By this means 

 the animal is better protected. The "deck" is a plate 



which has been de- 

 veloped internally to 

 help hold the animal 

 in the shell. 



The limpets are 

 modified prosobranchs. 

 They are bilaterally 

 symmetrical, and are 

 covered by a flat, coni- 

 cal shell, which is ap- 

 plied closely to the rock 

 all around the base in 

 such a way as to pro- 

 tect the animal within. 

 In some species (genus 



FIG. 160. Patella vulgata, seen from the . 1x , . 



ventral side. /, foot'; c/.i, circlet of gill * issurella *) there is an 



lamellae; m.e, edge of the mantle; mu, at- O p en i n g a t the apex of 



tachment muscle; si, slits in the attachment * . 



muscle; sh, shell; v, efferent branchial the shell through which 



vessel;*' aorta -,ve, smaller vessels. From the water ig expelled 

 the Cambridge Natural History. 



which has passed over 



the gills. Our common Eastern rock limpet is not per- 

 forated; it is known as Acmcea. 2 In Europe, limpets 

 (Patella, Fig. 160) are used as food ; but on our Eastern 

 coast they are too rare for this. 



The opisthobranch mollusks include a large proportion of 

 symmetrical shell-less species. The most familiar of these 

 are the nudibranchs. They may be found among hydroids 

 hanging from rocks, or in tide-pools. Our species are 

 usually less than 20 millimetres long. They are often 



little slit or fissure, 



, in full bloom, maturity. 



