118 CLAMS, OYSTERS, AND MUSSELS 



and size. They are usually found creeping on hydroids or 

 upon the seaweeds along the shore. 



Seashells. — The so-called "seashells" are the shells of 

 snail-like moUusks that Uve in the sea. The shells of these 

 moUusks are of many different shapes, colors, and sizes. 

 The cowries are favorites with collectors. The little oval, 

 sharp-spired periwinkles are common along the seacoast. 

 Others of these moUusks have very long, slender, many- 

 whorled shells. 



Squid, Cuttlefish, and Octopus 

 Class III. — Cephalopoda (head-footed) 



As the name indicates, these animals, which include the 

 squid, cuttlefish, octopus, etc., have footlike appendages on 

 the head. The appendages are really used for grasping, and 

 are called tentacles, or arms. Sometimes a shell is present, 

 and sometimes it is not. When present, the shell is usually 

 internal; but, in the nautilus, the shell is well developed 

 and external. 



The squid. — The body of the squid is long and slender 

 and incased in a thick, fleshy mantle in Ueu of a shell 

 (Fig. 65). On each side of the body, at the posterior end, 

 is a triangular fin used to guide the body in swimming. The 

 head is distinct, bears two prominent eyes and five pairs 

 of arms or tentacles, all furnished with cuplike suckers for 

 grasping its prey. One pair is usually longer than the 

 others, and each member of this pair is e^ipanded near the 

 end where it bears four rows of large suckers. The mouth 

 is in the center of the cluster of arms at their bases and has 

 two strong, horny, black jaws like the beak of a parrot. 

 Inside the body is a sac containing black pigment which is 



