120 MANUAL OF ZOOLOGY. 



The Alcyonaria differ numerically from the Zoantharia in 

 having their soft parts arranged in multiples of four, instead 

 of five or six, as in the latter. Their tentacles, too, are pin- 

 nate, and are not simply rounded. Numerically the Alcyon- 

 aria agree with the extinct order Riigosa, but the latter 

 invariably possess a well -developed sclerodermic corallum, 

 the thecae of which exhibit either septa or tabulae, or both 

 combined. 



With the exception of the single genus Haimeia, the 

 Alcyonaria are all composite, their polypes being connected 

 together by a common coenosarc, " through which permeate 

 prolongations of the somatic cavity of each, forming a sort of 

 canal system, whose several parts freely communicate," and 

 permit of a free circulation of nutrient fluids. Anatomically 

 the polypes of the Alcyonaria do not differ in any essential 

 particular from those of the Zoantharia; the numerical dis- 

 tinction being the one by which they are chiefly separated 

 from one another. The Alcyonaria are divided into four fami- 

 lies, viz., the Alcyonidce, the Tubiporida, the Pennatulidce, and 

 the Gorgonidce. 



FAMILY I. ALCYONID^:. This family is characterised by the 

 possession of a fixed actinosoma, which is provided with a 

 sclerodermic corallum in the form of calcareous spicula im- 

 bedded in the tissues. 



Alcyonium may be taken as the type of the family, and it is 

 well known to fishermen under the name of "Dead-men's 

 fingers." It forms spongy-looking, orange-coloured crusts or 

 lobate masses, which are attached to submarine objects, and 

 are covered with little stellate apertures, through which the 

 delicate polypes can be protruded and retracted at will. The 

 polypes communicate with one another by an anastomos- 

 ing system of aquiferous tubes, and the corallum is in the 

 form of cruciform, calcareous spicula scattered through its 

 substance. 



FAMILY II. TUBIPORID^E. In the Tubiporidcz, or "organ- 

 pipe corals," of which T. musica is a familiar example, there 

 is a well -developed sclerodermic corallum, with thecae, but 

 without septa. The corallum is composed of a number of 

 bright red, tubular, cylindrical thecae, which are united together 

 externally by horizontal plates or floors, which are termed 

 " epithecae," and represent external tabulae. The polypes are 

 usually bright green in colour, and possess eight tentacles 

 each. 



FAMILY III. PENNATULID^:. The Pennatulidce, or "Sea- 

 pens," are defined by their free habit, and by the possession 



