THE INVERTEBRATE LEGIONS 119 



such plantlike animals as anemones, sponges, hydroids, and sea squirts, in 

 the same way that some insects such as plant lice (aphids) live bv sucking 

 plant juices. Sea spiders are common in all seas, but they are so well camouflaged 

 by their shape and remain so still that they are not very often seen. 



Insects : Class Insecta — Figure 39 



Onlv one group of insects has invaded the sea, the water striders, familiar 

 bugs which shuttle across calm waters of wooded ponds, lakes, or streams. 

 Oceanic water striders, Halohates, are small and tropical in distribution. 

 They are predacious bugs with sucking mouths. They never enter the water 

 but live bv walking on it as a land animal walks on the ground. Just how these 

 little insects have adapted to live on the open expanse of ocean where there 

 is no shelter from waves and weather is not well known. They probablv feed on 

 small flying insects such as midges that fall on the open sea from the air. Thev 

 also may eat diatoms. 



MOLLUSCS: Phylum Mollusca 



The name "Mollusca" refers to the fact that these are soft-bodied animals. 

 Molluscs are nonsegmented, but thev have a head with tentacles and usually 

 with eyes. Thev usually move by crawling about on a foot, a broad flattened 

 area on the ventral surface. In the case of bivalves (clams and oysters) and 

 tooth shells, the foot acts as a digging organ and in the case of cephalopods 

 (squids and octopuses), it is formed into tentacles. The mollusc's outer body 

 covering is called the "mantle" and usually secretes a shell which protects the 

 soft body of the inhabitant. 



The molluscs form a gigantic group with about eightv thousand or more 

 species. However, this great arrav falls rather neatlv into five major groups, 

 each of which forms a rather compact unit, both as to form and general habits. 

 In general, molluscs are rather slow-moving, sluggish animals. The exception 

 to this rule occurs in the octopuses and squids, in which the nervous system is 

 among the best developed of all invertebrates. 



Chitons: Class Amphineura — Figure 40 



These are the most primitive of molluscs. The bodv is shaped like an oval 

 disc and always bears eight hard plates on the back for protection. There are 

 no tentacles. Some rather rare or deep-water chitons are wormlike in shape, 

 but the great majority adhere closely to the body plan described. They are all 

 animals of shallow, rocky shores where they adhere with their muscular foot, 

 often so tightly that they cannot be removed without breaking them. Chitons 

 browse on algae, using their tongues, which bear hard rasping teeth called a 

 "radula," to scrape their food from rocks. Bv day, chitons prefer to rest in 

 shady crannies or dark places on the undersides of rocks, but they wander about 

 freely at night. Chitons defend themselves by rolling into a ball like an 

 armadillo or pill bug. 



Chitons are found in all waters in the world. Thev are mostly under 3 inches 



