ACTINOZOA. 85 



The Aclmozoa are divided into four orders — viz., the Znantharia, 

 the Alcyonar.ia, the Rugosa, and the Ctenojjhora. 



Order 1. Zoantharia. 



The Zoantharia comprise those Aciinozoa in which the polypes 

 are furnished with smooth, simple, usually numerous tentacles, which, 

 Hke the mesenteries, are in multiples of six. The Zoantharia ai-e 

 divided into three groups, distinguished from one another by the 

 presence or absence of a coral, and by its structure when present. 



The first of these groups is termed Zoantharia malacodermata, or 

 " soft-skinned " Zoantharia, because the polypes are either wholly 

 destitute of a coral, or if there is one, it consists merely of little 



Fig. 48. — Actinia mescmhnjanthewnm, one of the Sea-Aiiemoncs. 

 (After .Johnston.) 



scattered spicules of carbonate of lime or grains of sand. Generally, 

 too, the organism is simple, and consists of no more than a suigle 

 polype. The best known of the members of this group are the 

 beautiful Sea-anemones or " animal-flowers " {Aetinidoi), which occur 

 so plentifully on every coast (fig. 48). It will be as well to descrilje 

 the structure of a sea-anemone somewhat in detail, as in this waj 

 a clear notion may be obtained of the general anatomy of the 

 Actinozoa. The body of an ordinary sca-aiiemone (fig. 48) is a 

 truncated cone or sliort cylinder, termed the "column," and is of a 

 soft leathery consistence. The two ends of the column are teimed 

 respectively the "base "and the "disc," the former constituting a 

 kind of sucker, by means of wliicli the animal cnn attach itself at 

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