88 THE MARINE AQUARIUM. 
themselves, and these are mostly soft bodied, having no 
shelly covering, and are protected only by the leathery 
integument which surrounds them, and the thousand 
weapons of offence and defence which they expand in the 
form of tentacles. Among the Polyzoa we meet with 
creatures that encase themselves in horny shells, or cal- 
careous coatings, such as the Madrepores, which, like 
submarine masons, elaborate the carbonate of lime which 
the sea supplies them with, into shelly retreats ; and the 
tubed Hydrioda, which construct winding galleries and 
convoluted tubes, from the mouths of which they protrude 
their fans and tentacles in search of prey. 
Among the higher orders of the Radiata we meet with 
the strange Sea Cucumbers and the Sea Urchins, and the 
Star fishes; and among the lower orders the Sea Ane- 
mones, many forms of which are described and figured 
in these pages. 
A Sea Anemone, then, is a Zoophyte belonging to the 
class ANTHOZOA, or flower-life, and the order HELAN- 
THOIDA, or sunflower-like creatures. The central disk of 
the sea flower is composed of the lips, which open into a 
mouth which communicates with the simple sac which 
constitutes the stomach, and the petals and fringes which 
surround it—now like the anemone, now like the sun- 
flower or the mesembryanthemum, or the richest car- 
nation that ever won for a florist a golden prize. The 
further subdivision is dependent on the details of indi- 
* vidual structure; and a large section—that of Actinia— 
comprehends most of those on which the aquarian 
bestows his patience in the work of domestication. 
