ARCHICCELOMATA. 177 



SuB-PiiYLUM III. — Bryozoa. — The Bryozoa are marine 

 and freshwater colonial forms. They are all practically seden- 

 tary and in many types there is great physiological division 

 of labour, some polypes degenerating into mere vibratile 

 processes or snapping pincers. 



The class Fhylactolcemata (with horseshoe-shaped lopho- 

 phore) are all freshwater types and the polypes are better 

 developed. 



The Gymnolcemafa (with circular lophophore) are 

 nearly all marine and have more modified polypes. 

 Their skeletons may be calcareous or chitinous and are, 

 as in the case of the hydroid zoophytes, constructed upon 

 the same principles of branching as plants. 



Sub-Phylum IV. — CHiETOGNAXHA. — This is a small 

 group for Sagitta and its allies. Sagitta is practically 

 typical of the sub-phylum. It is important, showing the 

 possibihties in the Archicoelomata of an active progressive 

 type, 



Sub-Phylum V. — Brachiopoda. — These are like Wald- 

 heu?iia, all two-shelled, and are divided into the hinged and 

 those without hinges. They are like the rest of the Archi- 

 ccelomata of ancient origin and some types, such as Ltngula, 

 with a long peduncle used as a motor organ, appear to have 

 remained constant in structure from the earliest geological 

 times. 



PHYLUM ARCHICCELOMATA. 



1. Coelomate tridermic metazoa with. piano-symmetry. 



2. No metameric segmentation, but a distinct archimeric segmenta- 



tion into three parts. 



3. Coelom well developed and divided more or less into parts 



corresponding with the segmentation. 



4. Nervous system simple, with dorsal brain, circumcesophageal 



ring and cords, often retaining its connection with the ectoderm. 



5. A simple blood-vascular system of hsemocoelic sinuses. 



6. Usually have a free larval pelagic development. 



7. Mostly marine and pelagic, sedentary or burrowing. 



M. 13 



