240 
WB NOH 
ANNULATA. 
SUB-PHYLUM ANNELIDA. 
. Metameric segmentation. 
nerve-chain with ganglia. 
Nan + 
Class I. 
ARCHIANNELIDA 
Lype—Polygordius. 
1. No sete on body. 
2. Prostomial tenta- 
cles, but no bran- 
chia. 
3. Dicecious. 
4. Larval develop- 
ment. 
5. Marine. 
. Paired lateral appendages often present. 
Class IT. 
PoOLYCHATA, 
Lypes—Arenicola 
and Nereis. 
Many sete on para- 
podia. 
Usually _ branchiz, 
cirri and tentacles. 
Dicecious. 
Indirect larval devel- 
opment (Trocho- 
phore). 
Marine, free-swim- 
ming or sedentary. 
- Ceelomate Metazoa with bilateral symmetry (plano-symmetry). 
. Muscles are arranged in definite circular and longitudinal layers. 
Excretory organs are paired nephridia (many). 
Class IIT. 
OLicocuata. 
Lype—Lumobricus. 
No parapodia and 
few seta. 
No branchiz, cirri 
or tentacles. 
Hermaphrodite. 
Direct development. 
Freshwater or terres- 
trial. 
. Nervous system is a brain above oesophagus, a circumoral ring and double ventral 
. A vascular system of vessels or sinuses and perivesceral caelom is usually present. 
Class IV. 
Hirvpinea (Disco- 
PHORA). 
Type—Hirudo, 
A pair of suckers and 
no parapodia. 
No branchie, cirri 
or tentacles, 
Hermaphrodite, 
Ccelom reduced to a 
dorsal and ventral 
sinus and other 
smaller parts,which 
communicate with 
the vascularsystem. 
Gonads have separate 
ducts to exterior. 
Free freshwater or 
marine, partially 
ectoparasitic. 
Susp-PHyLuM II.—AR1THROPODA. 
In the ARTHROPODA the body, as a rule, is enclosed in 
a thickened cuticular exoskeleton, which may or may not 
be further strengthened by calcareous particles. The 
paired appendages undergo a similar modification, pro- 
ducing jointed limbs. These are bent towards the ventral 
surface and serve to support the body. These appendages 
show far more adaptive modification into jaws, legs and 
feelers than in the lower sub-phylum. In many of the 
higher types of Avthropoda the body and its parts become 
compressed into a compact form, losing the elongated 
