This fossil of marine bristle worm tubes was 

 found on the beach at Sidmouth, England, and 

 dates back to the Mesozoic era. The worms 

 (Serpulidae) were true segmented worms. 



The peacock worm, a marine bristle worm, 

 builds a protective tube around its body 

 and anchors itself to coral or sand. Feather- 

 like gills enable the animal to breathe 

 and serve as food collectors. When alarmed, 

 the animal withdraws into its tube. 



came into existence in the shallow seas some 1 500 million years ago. 

 But we can do little more than guess what actually took place, 

 although it is a fair guess that plants were the first on the scene, 

 because only plants can make food out of non-living materials. 

 Still guessing, it seems reasonable to suppose that some plants lost 

 their ability to make their own food and began to feed on other, 

 simpler plants. As time passed groups of cells came to live together, 

 and the first simple seaweeds, sponges, and coelenterates came into 

 being. They moved about very little and their food requirements 

 were not complex. The ages sped past with little or no change, 

 until muscle fibers appeared in some of these creatures and they 

 began to stretch their arms, not merely to reach for food but to 

 move out in search of it. 



An animal can get from one place to another in a variety of 

 ways. It may crawl, walk, or swim, doing any of these in one of 

 several ways. Jellyfishes can swim, but not strongly enough to 

 counter the currents, so they mainly drift about. Sponges are mostly 

 fixed, but some kinds can drag themselves laboriously and very 

 slowly over the surface of rocks. Sea anemones remain fixed for 

 long periods, but they also can move slowly over the rocks, and a 

 few can inflate their "hollow stomachs," let go of the rock, and 

 float away. 



But none of these is locomotion in the real sense. Starfishes can 

 do better, but even their efficiency is limited by their body plan - 

 they are built on a radiate plan, meaning that they are without a 

 head end and a tail end that would structure them for efficient 

 locomotion. Little progress could be made, therefore, until such 

 an animal came on the scene. Let us now turn to another great 

 group of invertebrates - the worms. 



Anything small, elongated, and creeping is called a worm, but 

 the precise term for the marine animal in this group is "bristle 

 worm." A typical bristle worm has a mouth with a pair of stout 

 jaws at the head end of a long cylindrical body divided into a nu mber 

 of segments. On each segment is a pair of parapodia - outgrowths 

 of skin used for breathing — supporting one or more bristles. With 

 the aid of the bristles the worm can creep over the sea bed, burrow 

 in sand, or swim through the water. 



86 



