Chap. 28 ANNELIDS PIONEERS IN SEGMENTATION 569 



current of water goes in one end and out the other, kept in motion by the 

 worm's rhythmic fanning of the broad flaps near the middle of its body. Oxygen 

 and particles of food go in with the current. As before mentioned minute crabs 

 (Pinnixa) often live in the tube and share the "crumbs." The daily life of 

 Chaetopterus can be observed because it will live for long periods within a 

 glass U-tube in a salt water aquarium. In the dark it is silvery from its bio- 

 luminescence. 



The plumed worm, Diopatra ciipraea, is 10 to 12 inches long and is one of 

 the most beautiful annelids of the Atlantic Coast. It constructs a tube large 

 enough for the worm to turn around inside, with a chimney perfectly dis- 

 guised by shells and seaweed. It is common in shallows below the low-tide 

 line, from New England to South Carolina. 



Palolo worms, Eunice viridis, and their near relatives are the classic ex- 

 amples of spawning associated with the tides and moon. The Atlantic palolo 

 swarms a few hours before sunrise in June and July, shortly before the last 

 quarter of the moon. The Pacific palolo swarms in October and November, 

 near the last quarter. The Bermuda "fire worms" not only swarm but are 

 luminescent while they do so. In Harvey's Living Light there is an account of 

 their spectacular performance. A similar species {Odontosyllis phosphorea) 

 swarms on the western coast of North America. 



Class Hirudinea 



Leeches 



Leeches are segmented worms that hold on by suckers. They get about by 

 swimming and by looping over surfaces like measuring worms (caterpillars). 

 Holding onto the surface with its rear sucker, the leech stretches out its body, 

 attaches the front sucker to the surface and pulls the body forward. The rear 

 sucker then releases its hold and is placed close behind the front one so that the 

 body forms a loop (Fig. 28.15). The common name leech means to hang on 

 and gain thereby. The class name, Hirudinea, comes from the hirudin that a 

 leech injects into the wound as it bites and thus prevents the blood from 

 coagulating. 



Ecology. The majority of leeches live in fresh water; a few are marine; 

 others abound in swamps and the forests of the humid tropics. Some of them 

 feed on snails and worms; others are true bloodsuckers. As a group they are 

 wavering on the edge of parasitism but not wholly committed to it. Most of 

 them are predators, not more than 25 per cent are parasitic and many of these 

 stay on their hosts only while they are feeding. 



Leeches are acutely sensitive to vibrations and to extremely small amounts 

 of substances dissolved in water. If you press your finger against the bottom of 

 a dish containing leeches, they will at once begin to creep about, exploring the 



