108 



UNDERWATER GUIDE TO MARINE LIFE 



very important as the group which gave rise to the arthropods, the largest of all 

 phyla, which include insects and crustaceans. 



This phylum is divided into three major classes— earthworms, leeches, and 

 marine worms. Only the last of these will concern us, the marine worms or 

 Polychaeta. Two other small classes, the echiurids and sipunculids, are tacked 

 onto this phylum because they seem to have been derived from segmented worms. 



In habits, this group varies greatly, from errant (wandering), predaceous 

 worms to tube-dwelling, sessile plankton-feeding types, but the important thing 

 about segmented worms is that they have a well-developed nervous system and 

 a segmented muscular system so that rather refined movements are possible. 

 This is an important advance over the nonsegmented animals that we have 

 dealt with so far. 



Sexaal +a.il 



PALOLO WORM 

 Eu„,ce- 10 in. 



lft+rover+ «&, BUDDING, SEKUAL WORM 



Syllis-ea.ch 



PARCHMEMT WORM 



BRISTLE WORM 

 Hermoc(ice-U+. 



Fig. 35. Segmented worms. Adapted from the Reports of H.M.S. Challenger 



Cl 873-76^ and drawn from. life. 



Marine Worms: Class Polychaeta — Figure 35 



The marine worms are obviously segmented, and most of them are provided 

 with appendages on each segment called "parapodia," which bear bristles. 

 Parapodia represent the initial effort made by invertebrates to develop limbs. 

 They function as limbs, as gills, or in food-getting. 



