230 OUTLINE CLASSIFICATION OF ANIMALS 
3. ARACHNOIDEA, including spiders, scorpions, the king- 
crab, &c., as well as many parasites. They have no antennae, 
and the breathing organs are very diverse. 
The PHYLUM ECHINODERMA includes a great number 
of marine animals, of radiate form, often with limy skeletons. 
The living classes comprise the sea-urchins (Echinoids), star- 
fish (Asteroids), brittle-stars (Ophiuroids), sea-cucumbers 
(Holothuroids), and sea-lilies (Crinoids). 
The Phylum of ANNELIDS includes all the different kinds 
of segmented worms, including both the sea-worms and the 
earthworms. Among worm-like types we have also many 
parasitic forms, of minor importance so far as distribution is 
concerned, and such free-living forms as Rotifers. 
The PHYLUM COELENTERA includes a great number of 
aquatic, usually marine, organisms, often of great beauty and 
of great diversity. Among them we have sea-firs and their 
allies, and the fresh-water hydra (HyDROMEDUSAE) ; the sea- 
anemones, corals, alcyonarians, large jellyfish and related 
forms, all of somewhat more complicated structure (Scy- 
PHOZzOA); and finally those delicate iridescent bells which float in 
the open waters of the ocean, and constitute the CrENoPHORA, 
because of the delicate combs by means of which they swim. 
The sponges, all aquatic and mostly marine, constitute the 
PHYLUM PORIFERA, and the minute PROTOZOA, of great 
importance in that many parasitic forms are included, form 
a large phylum of very simple animals. 
