27 



An Aquatic Miscellany 



Ecological Intimacy. Ecologically, the animals described in this chapter are 

 closely related and they have shared the welfare of water for untold genera- 

 tions. They have gradually fitted into one or another of the numberless niches 

 in water, from ponds to oceans. They have many traits in common, also differ- 

 ences. The latter are the basis for their separation into several distinct groups. 



Most of these animals are marine. As adults they creep, burrow, or are 

 attached to rocks and plants, but in general the young swim about freely and 

 are carried by the ever shifting currents of water. The free-swimming young 

 of several of the groups resemble one another and are also similar to those of 

 annelids and mollusks (Fig. 27.1). They are trochophores (Gr. trochos, wheel 

 -f phoriis, to bear), the minute larvae which suggest that all of them used to 

 resemble one another throughout their lives, though they do not now. Even 

 the various adults meet over the same kinds of food. They consume bacteria 

 and silica-coated diatoms, and themselves provide protein and minerals for 

 their slightly larger neighbors. Rotifers, bryozoans, brachiopods and phoronids 

 are food-sifters relying on the transporting power of water and their own 

 equipment of tentacles and cilia to bring the harvest to their mouths. 



The animals of this "miscellany" do not lack conflicts and contrasts, dra- 

 matic in their vigor and precision. Carnivorous rotifers hunt down the water- 

 fleas with furious pounce. Arrow worms move up and down in the sea by the 

 time clock of light. In the morning and evening twilights, millions of them 

 swarm through the surface waters of the ocean. They arrive in them promptly, 

 remain while the amount of light is precisely right for them, and departing 

 sharply, spend other hours in the darkness of deep water. Also among the 

 miscellany is the lamp shell, Lingula, so like the fossils of its ancestors of 

 400,000.000 or more years ago, that its nickname is "living fossil." 



The classification of these groups has been rearranged several times and 

 changes are still being made. Some groups have long been recognized as unique 



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