— 2î — 



segmentation only evident in the young ; development with a 

 metamorphosis ,. Echiuroidea. 



external segmentation absent, or the body ringed 

 with annuli which are more numerous than the internal 

 segments ; development direct 



i' no division of the body externally ; five pairs of 

 ventrally placed parapodia ; parasitic 



Myzostomida. 



body externally ringed with annuli, 8-24 to each 

 internal segment 



without parapodia, and usually also without setae ; a sucker on 

 the posterior ,"and usually also one on the anterior end of the body; 

 3-12 annuli to each internal segment ; parasitic; mostly fresh water 



and terrestrial, a few marine Hirudinea. 



with ventrolateral parapodia and setae^ and with tracheiform organs ; 

 no suckers ; 12-24 annuli to each internal segment ; terrestrial 



Onychophora. 



P with a true skeleton forming an integral part of the body ; 

 development through a larva profoundly modified by 

 characters projected into it from the later stages through 

 acceleration of ontogeny, or direct; all the included 

 groups with variously developed « chordate » features 

 g' without gill clefts and a branchial skeleton, and without 

 a solid process from the anterior portion of the alimen- 

 tary canal serving as a supporting structure 

 h' body unsegmented externally, internally with not 

 more than three usually incompletely differentiated 

 segments ; no respiratory organs ; no superficial 

 skeleton 



i' body cavity disappearing in the adult, the body 

 becoming filled with gelatinous tissue serving to 

 coordinate and to transmit muscular force ; with 

 a retractile proboscis lying in a dorsal sheath which 

 extends almost or quite the whole length of the 

 body ; nervous system more or less annelid-like ; 

 excretory system planarian-like, but much reduced ; 

 ectoderm ciliated Nemertea. 



V body cavity persistent ; skeleton stiff viscous or 

 solid ; no proboscis ; nervous system not annelid 

 like ; excretory system not planarian like ; ectoderm 

 rarely ciliated 



attached and without a head ; during the metamorphosis from the 

 young to the adult stage the mouth moves upward and posteriorly 

 to a posterior position near the anus (as in the Calyssozoa, Polyzoa, 

 crinoids, barnacles, Pterobranchia and Tunicata) 



with an internal mesoblastic skeleton only; with a horseshoe 

 shaped polyzoan-like lophophore ; social, forming closely packed 

 aggregates of individuals living together in leathery tubes, though 

 each individual is entirely separate ï"rom the others.. . Phoronida. 

 k^ with an external covering composed of two (ventral) valves as 

 well as an internal skeleton ; solitary, but very common wherever 



found ' Brachiopoda. 



' free living and pelagic, elongate, with a rudimentary head including 

 an endocranial cartilaginous plate ; no vascular nor nephridial 



systems Chaetognatha. 



h^ body abruptly segmented externally, with five or 

 more segments ; respiratory organs present (very 

 rarely absent) ; with an articulated superficial skeleton 



(400) 



