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ANNULATA. 



SUB-PHYLUM ANNELIDA. 



Coelomate Metazoa with bilateral symmetry (piano-symmetry). 



Metameric segmentation. 



Nervous system is a brain above oesophagus, a circumoral ring and double ventral 



nerve-chain with ganglia. 

 A vascular system of vessels or sinuses and perivesceral co^lom is usually present. 

 Paired lateral appendages often present. 



Muscles are arranged in definite circular and longitudinal layers. 

 Excretory organs are paired nephridia (many). 



Class I. 



Archiannelida 

 Type — Polygordius. 



1. No setae on body. 



2. Prostomial tenta- 



cles, but no bran- 

 chiae. 



3. Dioecious. 



4. Larval develop- 

 ment. 



Class II. 



POI.YCH/ETA. 



Types — A renicola 

 and Nereis. 



Many setae on para- 

 podia. 



Usually branchiae, 

 cirri and tentacles. 



Dioecious. 



Indirect larval devel- 

 opment (Trocho- 

 phore). 



Marine, free -swim- 

 ming or sedentary. 



Class III. 



Oligoch/eta. 

 Type — L unibricus. 



No parapodia and 

 few setae. 



No branchiae, cirri 

 or tentacles. 



Hermaphrodite. 



Direct development. 



Freshwater or terres- 

 trial. 



Class IV. 



HiRUDINEA (Disc 



phora). 

 Type — Hirudo. 



A pair of suckers ai 

 no parapodia. 



No branchiae, ci] 

 or tentacles. 



Hermaphrodite. 



Coelom reduced to 

 dorsal and ventr 

 sinus and othi 

 smaller parts, whi( 

 communicate wi 

 the vascu lar systei 



Gonads have separa 

 ducts to exterior. 



Free freshwater 

 marine, partial 

 ectoparasitic. 



Sub-Phylum II. — Arthropoda. 



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 Arthropoda the body and its parts become 

 compressed into a compact form, losing the elongated 



