POLYCHJETA 283 



budding. In many the anterior part of the body is sexless and is called 

 the atoke, while the hinder part is sexual and is called the epitoke, these 

 two portions being different in appearance; in some the epitokes break 

 off from the atokes and swim about independently, while the atokes bud ofE 

 new epitokes. The palolo worm of the Samoan and Fiji Islands is the 

 epitoke of Leodice viridis, which comes to the surface in great numbers at 

 the full of the October moon to breed, and which are caught by the natives 

 for food. The palolo worm of the Atlantic is L. fucata. In Syllis the 

 epitoke forms a new head; in Autolytus this happens before separation. 



In certain species of Nereis heterogony is present, a small pelagic 

 form alternating with a large one which lives at the bottom. 



Distribution and Habits.— A veiy few polychaets live in fresh water 

 {Manayunkia in the Schuylkill, a Nereis in California, and several others) ; 

 the remainder, which are marine, are almost all bottom animals which 

 burrow in the sand or in rocks or live in tubes they have built for 

 themselves of lime or other material. They are found at all depths and 

 are usually numerous in all parts of the world. The free-swimming poty- 

 chaets are predaceous animals, while the sedentaiy ones live on all kinds of 

 organic substances ; a few are parasitic, and a number commensalistic. 



The order contains about 39 families and 2,500 species grouped in 7 

 suborders. 



Key to the suborders of Polychceta : 



Oi Worms free-swimming or burrowing, a few tubicolous ; head distinct, with 



tentacles and palps 1. Nebeidiformia 



Ci Worms tubicolous or burrowing ; head not so distinct and not provided 

 with both tentacles and palps ; sometimes with neither. 

 6i Peristomium does not project forwards in form of a collar. 



Ci Head with gill filaments (except in Cirratulidae) 3. Terrebelliformia 



Ca Head without gill filaments. 



di One pair of long peristomial cirri present 2. Spioniformia 



(^2 One pair of retractile tentacle-like organs on head.. 4. Capitelliformia 

 ds Head with no appendages (except in ChlorhcFmidae) ... .5. Scoleciformia 

 &2 Peristomium projects forward in form of a collar. 



Ci Peristomial collar not setigerous 6. Sabelliformia 



Cz Peristomial collar setigerous 7. Hermelliformia 



Suborder 1. NEREIDIFORMIA.* 



Well-developed tentacles and palps present; peristomial cirri almost 

 invariably present; parapodia well developed, with internal skeletal rods 

 called acicula and ventral and dorsal cirri; proboscis present, often 

 with prehensile hooks; worms predacious, a few forming tubes: about 

 13 families. 



* See "Die Borstenwurmer," by E. Ehlers, 1864. 



