CHAPTER X 
CHAETOPODA 
Archiannelida, 
Naidomorpha—JNais, Chaetogaster. 
ongocasta{ becoming — Lumbricus, Megascolides, 
Eudrilus, Perichaeta. 
Errantia—WNereis, Aphrodite, Eunice, Tomopteris. 
Sedentaria—Arenicola, Sabella, Capitella. 
Chaetopoda 
Polychaeta 
CHARACTERISTICS.—Segmented animals, with a more or less pro- 
minent prostomium or region in front of the mouth.  Loco- 
motion effected by cilia, or by setae implanted in the body 
wall or borne by lateral processes of the body termed para- 
podia. Hach seta ts the product of a single cell. The 
segments are divided externally by grooves, internally by septa. 
A pair of nephridia are typically found in each segment. 
The Chaetopoda are divided into three sub-classes: the 
ARCHIANNELIDA, the OLIGOCHAETA, and the POLYCHAETA. 
ARCHIANNELIDA. 
CHARACTERISTICS.— Marine worms with small prostomium. The 
segmentation of the body is externally marked by rings of 
ciliated cells, and by slight grooves. There are no setae or 
parapodia or branchiae, but the head bears one or more pairs 
of tentacles. The longitudinal muscles are in four bands. 
The nervous system retains its connection with the hypodermis 
throughout life. The head bears a pair of ciliated grooves. 
The Archiannelida comprise a group of minute marine 
animals, which are to some extent intermediate between the 
Turbellarians and the Chaetopoda. The group includes four 
genera: Polygordius, Protodrilus, Histriodrilus, formerly known 
as Iistriobdella and classified with the leeches, and Dinophilus. 
