280 ANNELIDA 



Key to the classes of Annelida: 



©1 No suckers or sucker-like organs present (except in the Discodrilidae) ; 

 segmentation usually distinct externally. 

 bi No setae (except in Chwtogordiiis) or parapodia present. 1. Archiannelida 

 &2 Setae present 2. Cii^topoda 



c^ Suckers or sucker-like organs present. 

 bi Body ringed externally with a terminal sucker at each end ; leeches. 



3. HiRUDINEA 



bz Body flat and oval in shape with 5 pairs of parapodia and 4 pairs of 



sucker-like organs ; parasites on echinoderms 4. Myzostomida 



Class 1. ARCHIANNELIDA. 



Primitive, marine worms of small size, which are probably near the 

 base of the line of the Annelida, having many characters which ally them 

 to larval polychaets: 2 isolated, genetically unrelated families. 



Key to the families of Archiannelida: 



Oi Body with 5 or 6 segments, marked by ciliated bands 1. Dinophilidae 



©2 Body with numerous segments 2. Polygordiidae 



Family 1. DINOPHILIDAE.* 



Minute, marine worms living among seaweed; body short, thick, and 

 cylindrical, and made up of a head or prostomium, a trunk consisting of 

 5 or 6 segments, and a telson or tail; head with a pair of 

 eyes, 2 bands of cilia and tactile bristles, no tentacles 

 being present; each segment with 1 or 2 bands of cilia; 

 ventral surface also ciliated; sexes separate and develop- 

 ment simple, the worm becoming adult at a stage resem- 

 bling a polychaBtous larva: 1 genus and about 9 species, 3 

 American. 



DiNOPHiLTJS Schmidt. With the characters of the 

 family. 



D. pygmaeus Verrill. Length .7 mm. ; width .16 mm. ; 

 trunk segments 5; color whitish: Woods Hole, on piles. 

 D. gardineri A. Moore. Color orange red ; trunk seg- 

 ments 6; body ciliated in addition to the ciliated bands: 

 Woods Hole, in brackish pools. 

 D. conklini Nelson (Fig. 448). Length .5 to 1 mm.; colorless; trunk 

 segments 6: New Jersey coast. 



Family 2. POLYGORDIIDAE. 



Small, marine annelids in which the segmentation is completely 

 equivalent and often indistinctly marked extemally or not at all, and 



• See "Dinophilidae of New England," l>y A. E. Vorrill, Trans. Conn. Acad., Vol. 

 8, p, 457. "The Morphology of Dinophilns conklini n. .sp.," by J. A. Nelson, Proc. 

 Acad. Nat. Sci., Phila., Vol. 59, p. 82, 1907. 



