154 MANUAL OF ZOOLOGY. 



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

 antharia, the Alcyonaria, the Rugosa, and the Ctenophora; 

 but the last is sometimes placed amongst the Hydrozoa, and 

 it has been recently proposed to remove the Rugosa also to 

 the same class. 



ORDER I. ZOANTHARIA. The Zoantharia, Hexacoralla, or 

 "Helianthoid Polypes," are defined by the disposition of their 

 soft parts in multiples of five or six, typically the latter, and by 

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

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

 a " sclerodermic" corallum, in which the septa in each corallite, 

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



The above characters, though distinctive of the Zoantharia 

 as an order, are not capable of universal application, since the 

 disposition of the mesenteries in sixes cannot be always re- 

 cognised, and the tentacles are in rare instances fringed with 

 lateral processes ("pinnate"). 



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 sec- 

 tion of the Zoantharia there is either no corallum or a pseudo- 

 corallum in the form of adventitious spicules scattered through 

 the soft parts. The "actinosoma" is usually composed of but 

 a single polype. (The term "actinosoma" is a very con- 

 venient 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 

 Actinidx will require a somewhat detailed examination, since 

 they may be taken as typical of the entire class of the 

 Actinozoa. 



FAMILY I. ACTINID^E. The members of this family are 

 commonly known as Sea-anemones, and are distinguished by 

 having no corallum, or a spurious one, by being rarely com- 

 pound, and by having the power of locomotion. 



The body of a Sea-anemone (fig. 70, a) 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. 

 Most Sea-anemones fix themselves by the base to some foreign 

 object a stone or a living animal but others (Peachia and 



