STRUCTURE OF THE TURBO PICA. 



43 



from the shape of the opening, resembling a human ear. Man* 

 of these gasteropods are of considerable size. One species is 

 found on the shores of the Mediterranean. 



ORDER OF FECTXNXBRANCHIATA.* 



26. This division of the class of Gasteropods is the most 

 numerous in genera and species : it comprises nearly all the 

 mollusca, in which the shell is univalve and spirally twisted, 



vb b ab ov 



d 



Fig. 32. ANATOMY OF A PECTINIBRANCH GASTEROPOD. Turbo Pica (See Jig. 44). 



Explanation of Fig. 32. Anatomy of a pectinibranch gasteropod (the 

 Turbo pica\ to show the arrangement of the respiratory cavity : p. the foot 

 of the animal ; o. the operculum ; t. the trunk ; ta. the tentacles ; y. the 

 eyes ; m. the mantle, split open longitudinally so as to expose the respi- 

 ratory cavity : /. the anterior edge of the mantle, which in its natural po- 

 sition covers the back of the animal, and leaves there an opening or great 

 slit, through which the water reaches the branchiae ; b. the branchiae : vb. 

 the branchial vein which goes to the heart (c) ; ab. the branchial artery ; 

 a. the anus ; i. the intestine ; e. the stomach and liver ; ov. the oviduct. 

 Above the nucha or nape, we see the cephalic (nervous) ganglion, and the 

 salivary glands ; d. fringed membrane, which below borders the left side 

 of the opening of the respiratory cavity. 



* Pec'tinibranchia'ta. From the Latin, peclen, a comb, and branchta, 

 gills ; because the branchiae or gills (fg. 32, 6) resemble a comb in form. 



26. What are the peculiarities of the pectinibranch ga'steropods ? ta 

 what parts of the shell do we find the respiratory cavity ? 



