268 
COMPARATIVE ZOOLOGY. 
fringed “arm,” generally coiled up, and supported by a 
calcareous framework. The animal, having no gills, re¬ 
spires by the arms and the mantle. Brachiopods were 
once very abundant, over two thousand extinct species 
having been described; but less than a hundred species 
are now living. 137 They are all marine, and fixed; but of 
all Worms, they enjoy the greatest range of climate and 
depth. 
Class VI.—Annelides. 
The Annelides include the highest and most specialized 
Worms. They have many segments, spines or suckers 
for locomotion, a superoesophageal brain, a ventral chain 
Fig. 223.—Marine Worm (Cirratulus grandis), with extended cirri. Atlantic. 
of ganglia, and a closed blood-system. There are three 
main divisions: the flattened Leeches, without definite 
segments or bristles, and with suckers for locomotion ; the 
