386 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1923 



semblance to others of their kind, develop a mass of roots through 

 which, plantlike, they absorb the juices of their host. 



The seapeaches and other large sea squirts are familiar to all 

 fishermen on our coasts. They have a sieve inside of them by means 

 of which they strain small organisms from the water, after the man- 

 ner of the salps. 



The brachiopods, which look like bivalve mollusks but are really 

 very different, mostly live attached, though a few burrow into mud. 

 Their food-collecting mechanism is in general similar to that of 

 the polyzoans and phoronids, to which they are supposed to be re- 

 lated. One of them, called the snake's head, is very common in 

 suitable localities on the New England coast below the low -tide mark. 



Some bivalve mollusks live attached to firm supports, like the 

 oysters of our shores, while many others, like the clams and razors, 

 live buried in the mud. Some, like the mussels, attach themselves 

 with slender silken threads, as all do when very young. The qua- 

 hogs or hard-shelled clams, from which the Indians used to make 

 their wampum, and other forms lie exposed in quiet places on the 

 bottom. A few, like the sea dates or pholids, bore into rock and 

 sometimes in great numbers into breakwaters, while the shipworms 

 or teredos, which are not worms at all but mollusks, tunnel into 

 wood and feed upon it, like the larvae of boring insects in the for- 

 est trees. Most of the unattached bivalves can move about, though 

 rather slowly; a few are quite active, like the razor shells, and the 

 scallops are more active still, and can even swim. 



Many worms, while not attached themselves, live in tubes of their 

 own construction attached to other objects or partly rooted in the 

 mud. 



Of animals which live wholly exposed or hiding away in burrows, 

 holes, and crevices and among the roots of plants, there are multi- 

 tudes of conchs, whelks, drills, periwinkles, and other snaillike crea- 

 tures, of crustaceans of very many sorts, and jointed worms of many 

 different types, together with nemerteans, some of which are very 

 large, priapulids, sipunculids, and flatworms. Fishes, of course, are 

 everywhere. 



Besides the abundance of attached animals, especially of the colo- 

 nial types, the coastal regions are mainly characterized by the great 

 development of three groups of animals which are almost or quite 

 unrepresented in the open sea. These are the bivalve, the gastropod 

 or snaillike mollusks, and the echinoderms, including the starfishes, 

 the brittlestars, the sea urchins, the sea cucumbers or holothurians, 

 and the crinoids. The first two are most abundant along the shore, 

 becoming much less common in deeper water, while the echinoderms 

 rapidly increase in relative abundance with increasing depth. Prac- 

 tically all the members of these three groups are sluggish animals, 

 most of them able only to crawl slowly, though a few bivalves and 



