

CCELENTEKATA : ACTINOZOA. 99 



the Sea- anemones, possess a small amount of locomotive 

 power ; and one order, the Ctenophora, is composed of highly 

 active, free -swimming organisms. Some of the Actinozoa are 

 unprovided with any hard structure or support, as in the Sea- 

 anemones and in all the Ctenophora; but a large number 

 secrete a calcareous or horny framework, or skeleton, which is 

 termed the ' coral,' or 'corallum.' In one family the corallum 

 appears to be siliceous. 



The Actinozoa are divided into four orders, viz. : the Zo- 

 antharia, the Alcyonaria, the ' Bugosa, and the Ctenophora ; 

 but the last is sometimes placed amongst the Hydrozoa, and it 

 has been recently proposed to remove the Bugosa also to the 

 same class. 



ORDER I. ZOANTHARIA. The Zoantharia are defined by the 

 ition of their soft parts in multiples of five or six, and by 

 the possession of simple, usually numerous, tentades. There may 

 be no corallum, or rarely a ' sclerobasic ' one. Usually there is a 

 1 sclerodermic ' corallum, in which the septa in each corallite, like 

 the mesenteries, are arranged in multiples of five or six. 



The Zoantharia are divided into three sub-orders, the Zoan- 

 tharia Malacodermata, the Z. sclerobasica, and the Z. scleroder- 

 mata ; according as the corallum is entirely absent or very 

 rudimentary, is * sclerobasic,' or is ' sclerodermic.' 



SUB-ORDER I. ZOANTHARIA MALACODERMATA. In this section 

 of the Zoantharia there is either no corallum or a very rudi- 

 mentary one, in the form of a few scattered spicules. The 

 ' actinosoma ' is usually composed of but a single polype. 

 (The term ' actinosoma ' is a very convenient one to express 

 in the Actinozoa, what 'hydrosoma' expresses in the Hydrozoa, 

 namely, the entire organism, whether simple or compound.) 



There are three families in this section, of which the Acti- 

 nidce will require a somewhat detailed examination, since they 

 may be taken as typical of the entire class of the Actinozoa. 



FAMILY 1. ACTINID.E. The members of this family are 

 commonly known as sea-anemones, and are distinguished by 

 having no evident corallum, by being rarely compound, and 

 by having the power of locomotion. 



The body of a sea-anemone (fig. 26) is a truncated cone, or 

 a short cylinder, termed the 'column,' and is of a soft, 

 leathery consistence. The two extremities of the column are 

 termed respectively the ' base ' and the ' disc,' the former 

 constituting the sucker, whereby the animal attaches itself at 

 will, whilst the mouth is situated in the centre of the latter. 

 Between the mouth and the circumference of the disc is a flat 

 space, without appendages of any kind, termed the ' peristomial 

 space.' Round the circumference of the disc are placed 



H 2 



