78 Invertebrata. 



2. Unjointed or obscurely segmented minute forms, 



with ciliated head-lobes = Class Rotatoria. 



3. Parasitic, flat-bodied forms, with no body cavity, 



and provided with suckers = Class Cotylidea. 



4. Parasitic forms with no suckers nor digestive 



canal, and with a hook-bearing proboscis = 

 Class Acanthocephala. 



5. Cylindrical, unjointed, non- ciliated forms, with 



digestive canal and body cavity, mostly para- 

 sitic = Class Nematelmia. 



6. Segmented forms with a proboscis, and convoluted 



intestine, non-parasitic = Class Gephyrea. 



7. Segmented, bristle-clad worms with no suckers. 



moderate intestine, non -parasitic = Class 

 Chaetopoda. 



8. Segmented, unbristled, sucker-armed, external 



parasites = Class Hirudinea. 



9. Sessile, one-jointed, colony-building worms living 



in cells and with a crown of protrusible tenta- 

 cles = Class Bryozoa. 



10. Sessile or free, one-jointed worms, with one nerve 

 ganglion but no protrusible crown of tentacles 

 = Class Tunicata. 



CHAPTER XV. 



SUB-KINGDOM VI. MOLLUSCA, SOFT-BODIED ANIMALS. 



THIS division includes all such forms as oysters, 

 whelks, snails, and cuttlefishes. Most of these are 

 aquatic and in none is there an inner skeleton (except 

 some small gristly organs in cuttlefishes) nor are there 



