170 MARINE INVERTEBRATES 
Genus Cerebratulus 
C. angulatus. Olive-green, with light dorsal stripe. 
GENUS Cosmocephala 
C, ochracea. Two to three inches long when extended; gray or 
yellowish-white, and mottled by the internal organs showing through 
the translucent body; line of lighter color down the back; anterior end 
often orange-colored. It is common near low-water mark under stones 
and in the dead tubes of Serpula. 
Genus Polina 
P. glutinosa. One to two inches long; color orange or light yellow, 
with a faint line of deeper color down the center of the dorsal surface ; 
very slimy; eyes numerous, in oblique lines on the head. Found in 
tide-pools on alge. 
PHYLUM NEMATHELMINTHES 
ROUNDWORMS 
The worms of this phylum have the general name of round- 
worms, which distinguishes them from the flatworms of the pre- 
ceding division and from the segmented worms of the Annulata. 
The body is elongated, cylindrical, smooth, and pointed at both 
ends. With few exceptions, they are parasitic. 
A few of the nematode species are free, living under stones 
and among seaweeds at about low-water mark. 
CLASS NEMATODA 
Genus Pontonema 
P. marinum. Slender, white, smooth, active, cylindrical; con- 
stantly coiling and uncoiling itself. 
PHYLUM ANNULATA 
SEGMENTED WORMS 
The name of this phylum expresses the principal characteristic 
of the group of worms which have elongated bodies composed 
of series of short parts, or ring-like divisions. Each one of these 
segments contains a separate and similar set of internal organs. 
