566 EVOLUTION OF ANIMALS Part V 



England coast, mainly in the low tide range. It is a ravenous hunter, swims at 

 a good speed, and can grapple worms larger than itself. Clamworms construct 

 loose flexible tubes on a base of sticky mucus that catches the sand and 

 broken shells that disguise their chimneys. Like earthworms, they stretch out 

 of their tubes at night but day and night they are preyed upon by birds and 

 fishes. 



The Outer Tube — Protection, Locomotion, and Support. The greenish skin 

 is covered by iridescent cuticle like that of the earthworm. All of the segments 

 are externally similar except the head (Fig. 28.12). On each side of the seg- 

 ments there is a flattened fleshy lobe the parapod or "side foot" bearing bundles 

 of bristles. 



Clamworms and earthworms greatly resemble one another but are products 

 of unlike experience. For untold generations clamworms have lived in the 

 sea, swimming after their prey and away from their enemies. For an equally 

 long time streamlined earthworms have bored through the ground, swallowing 



I. 



Prostomium 

 a soft lip 



Sucking 

 mouth 



Head of eorthwornija herbivorous bur/ower: I. dorsal, 2. ventral view 



Palp 

 Prostomium 



Eyes 



Tentacles 



Head of clam worm, an active carnivore: 

 Dorsal views I. Jaws withdrawn, 2. Grasping jaws extended 



Fig. 28.12. Upper, head of the herbivorous burrowing earthworm with only 

 primitive light and touch receptors and no oral armature. Lower, head of the 

 active predatory clamworm equipped with clutching jaws and relatively complex 

 eyes. 



