I12 . INVERTEBRATE ANIMALS. 
anatomy the Ophiurozdea differ considerably from the true star- 
fishes, to which they are most nearly related, but these differ- 
ences do not require further notice. 
The habits of the brittle-stars and sand-stars are various, but 
many of them may be found in rock-pools or under stones at 
low water on our own shores. 
ORDER IV. CrINOIDEA.—In this order are comprised Echino- 
dermata, in which the body is fixed, during the whole of a 
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big. 46.—Comatula rosacea. a Free adult; 4 Fixed young (after Forbes). 
portion of the existence of the animal, to submarine objects by 
means of a jointed flexible stalk or column. The Crinoidea 
were formerly very numerous, both individually and in types, 
but they are.represented at the present day by but a small 
number of living forms, of which one only (the feather-star) 
is at all of common occurrence. The body in the Crinoids con- 
sists of a central disc or cup formed of calcareous plates, and 
protecting the body of the animal. From the margins of this 
cup spring five or more arms which are arranged in a radiating 
