The Paddle-footed 



Annelids {ClassPolychaem) 



When a coastal fisherman picks up a clamworni 

 to put it on his hook, he needs to look carefully and 

 seize the animal close behind its apparent head. Oth- 

 erwise he is almost certain to be bitten. The clam- 

 worm Nereis has a pair of horny jaws deep down in 

 its body. To defend itself or to take prey, the worm 

 everts its pharynx and exposes its two jaws, spreading 

 them widely. It can give quite a painful nip as it 

 presses the jaw teeth against a person's skin and then 

 attempts to withdraw its pharynx. 



A novice gives no thought to the fact that a more 

 delicate victim would have been torn apart, a piece 

 of it swallowed as the clamworm's dinner. He is too 

 amazed as well as chagrined at having dropped his 

 bait as though it were a snake. 



Some kinds of Nereis are as big as small snakes. 

 Nereis virens, found on both coasts of America in 

 cooler water and in northern European mud flats as 

 well, reaches a length of 18 inches in New England. 

 Its body is a handsome reddish brown, showing an 

 iridescent greenish sheen. From Long Island south- 

 ward, shelly bottoms are home to Nereis pelcii^ica. a 

 more tapering animal rarely more than 8 inches in 

 length. Sandy shores seem more suited to Nereis siic- 

 cinea ( Umbata ) . 



On European coasts the sea worm used for bait is 

 most frequently Nereis cultrifera. the chainworm or 

 ragworm, whose "rags" are its paddles, which droop 

 like wet cloth when it is removed from the sea. 



In its native element, a sea worm's paddles are ex- 

 tremely important. Without them the muscles of the 

 body wall could do little to promote locomotion while 

 the worm was lying on the bottom or surrounded by 

 water. But members of the class Polychaeta have the 

 body wall extended into one pair of paddles (para- 

 podia) on each of the many segments. Stiff bristles, 

 for which the class was named, support the paddles 

 and hold them almost at right angles to the body. The 

 paddles may be slightly fleshy or mere thin vanes, yet 

 they provide a hold on the water next to the worm 

 and make eflicient the locomotory movements of 

 muscles in its body wall. 



Among the largest of these paddle-footed swim- 

 mers is 3-foot Nereis brandti of America's Pacific 

 coast. These worms, which are as broad-bodied as a 

 garter snake, swim to the ocean's surface at night. 

 Scientists sometimes wonder how a "sea serpent" of 

 this kind would impress a slightly inebriated fisher- 

 man in a rowboat on a protected bay. He might need 

 to do no more than shine a flashlamp over the side 

 to see a few of the giants moving through the dark 

 water, their paddles glistening in the light. 



The Greek mythmakers peopled the Mediterra- 

 nean with between fifty and a hundred nereids, and 

 pictured them in human form, riding sea horses. To- 

 day's annelid worms in salt water can be almost as 

 unbelievable when they ready themselves for repro- 

 duction. Even closely similar kinds show specific fea- 

 tures in the methods used in starting a new generation 

 on its way. 



Nereis and its nearest relatives introduce altera- 

 tions even in parts of the body not intimately con- 

 nected with production of eggs or sperms. The eyes 

 enlarge; the paddles change form; and for many 

 years the sexual stages were believed to be members 

 of a different genus (Heteroiiereis). They are still 

 referred to as heteroneieid individuals. 



The male heteronereid is regularly much smaller 

 than the female, and often almost white with sperm 

 cells showing through the body wall. The female het- 

 eronereid is usually heavy with reddish eggs, and 

 swims much more stiffly and sedately. The males 

 spiral in dizzy paths. 



On the Pacific coast of America, Nereis vexillosa 



Clamworms such as Nereis virens are the fish- 

 worms of the sea. M night they swim or creep over 

 the bottom, feeding on dead clams and other bits of 

 food. Bv day thev often reach food through the mud, 

 burrowing up to it from underneath. (Long Island, 

 New York. Ralph Buchsbauni) 



