Chap. 28 



ANNELIDS PIONEERS IN SEGMENTATION 



553 



Fig. 28.1. Tube-building annelids; peacock worm, Sabella pavonia (12 to 15 

 inches long). This and similar species live in British and North American tide 

 waters. The feathery plumes are glorified breathing organs and food traps that 

 emerge from the tubes and spread fanwise in the water like iridescent flowers. 

 (Photograph courtesy, Douglas P. Wilson, Marine Biological Laboratory, Plym- 

 outh, England.) 



cessful, and widespread over the world — some 6500 species in all. They live 

 in soil and fresh water but are most numerous in the sea. There they live in 

 the shallows and between the tide lines, at the surface, and on the bottom at 

 great depths. Water is their natural home. Earthworms flourish in moist soil, 

 and punctually come to the top in warm spring rains. 



Food. Annelids feed heavily on bacteria and on decayed plants; among sea- 

 weeds, as well as inland gardens, they clear space by eating and fertilize 

 it with their own bodies. There are predators among them, clamworms preying 

 upon smaller worms, some leeches living on smaller invertebrates, others 

 sucking blood. Annelids are in turn rich forage for larger predators in the 

 water and on land — crabs, lobsters, and fishes that hunt over the coastal bot- 

 toms, gulls that pick the seaweeds, robins seizing earthworms at the surface 

 of the soil, and ground moles catching them below it. By eating and being 

 eaten, they help to check the unbalance of too few or too many. 



Ways of Living. Burrowing annelids are successful animals but the tube- 

 making ones far outdo them in variety of form and habit (Figs. 28.1, 28.2). 



