ANIMAL RELATIONSHIPS . 
253 
PROTOZOA. 
'classes. 
Rhizopoda move by pseudopodia. Examples of 
this class are amoeba and chalk-animals. 
Infusoria move by cilia. Examples of this class 
are the bell animalcules and paramecium. There 
are other classes of Protozoa. 
PORIFERA. 
Keratose sponges have skeletons made of horn-like 
material. 
Calcareous sponges have skeletons composed of spic¬ 
ules of carbonate of lime. 
Silicious sponges have skeletons composed of 
quartz-like material, or of a combination of sili¬ 
cious spicules and silk-like fibres. 
These groups are not strictly classes. All sponges 
belong to the class Porifera. 
CCELENTER AT A. 
'CLASSES. 
Hydrozoa have the mouth at the top of a sort 
of proboscis. The entire body-cavity is a 
digestive cavity. Hydra, hydractinia, cam- 
panularia, sertularia, and many kinds of 
jelly-fish belong to this class. 
Scyphozoa are marine jelly-fishes. 
Actinozoa have the mouth-opening into a 
stomach-cavity distinct from the body-cav¬ 
ity. The body is also divided by radiating 
partitions. Sea-anemones and coral animals 
belong to this class. 
Ctenophora are transparent or nearly trans¬ 
parent comb-jellies. 
ECHINQPERMATA. 
CLASSES. 
Asteroidea are animals resembling the com¬ 
mon starfish. 
Ophiuroidea are animals resembling the 
sand-stars. 
Echinoidea are animals resembling sea- 
urchins. 
Crinoidea are stemmed forms. As fossils 
they occur in great abundance. They are 
known as stone-lilies. 
Other classes of Echinodermata are largely 
fossil forms. 
VERMES. 
No attempt is here made to give classes of Vermes. 
Instead of Vermes many authors now name several sub¬ 
kingdoms or phyla. Some of these are as follows: 
Platyhelminthes, or Flatworms. These are worms of 
low organization, including parasites like the liver- 
4 fluke and tapeworm. 
Nemathelminthes, Roundworms. These low forms 
have cylindrical bodies. The trichina belongs here. 
Rotifers , Polyzoa , and Brachiopoda have been vari¬ 
ously classed, often as members of the sub-kingdom 
Vermes. Their position is not fully settled. 
