IV PHYLUM CCELENTBRATA i^Oi 



The tentarks in Zoantharia are usually very numerous, and in 

 nearly all cases have the form of simple gi(ne-finger-like out- 

 pushings of the disc. In Edwardsia, however, they may be 

 reduced to sixteen, and in some genera of Sea-anemones they are 

 branched. In the Antipatharia (Fig. 150) they \ary in number 

 from six to twenty-four. When more than six are present, six 

 of them are larger "than the others. 



Fig. 150.— Antipathes ternatensis, portion of a branch, showing three zooids and the horny 

 axis hesot with sphies. (From the Ouiibiidge Natural History, after Schultze.) 



In the Alcyonaria, on the other hand, the tentacles, like the 

 mesenteries, are eight in number and are always pinnate, i.e. 

 slightly flattened and with a row of small braiichlets along 

 each edge (Fig. 144). ifany Actiniaria have the tentacles 

 perforated at the tip (Fig. 138, A, 'p.)\ and in some species 

 these organs undergo degeneration, being reduced to apertures 

 on the disc, which represent the terminal pores of the vanished 

 tentacles and are called domulia. 



Many Sea-anemones possess curious organs of offence called 

 acontia (Fig. 138, A, and Fig. 157, nc). These are long 

 delicate threads springing from the edges of the mesen- 

 teries: they are loaded with nematocysts, and can be protruded 

 through minute apertures in the column, called " port-holes " or 

 cinclides (en.). 



finteric System.— The gtdlet in the Actiniaria presents some 

 remarkable modifications. It is usually a compressed tube with two 

 siphonoglyphes, but in Zoanthus and some other genera the ventral 

 gullet-groove alone is present (Fig. 143, B), and in Gyractis both 

 grooves arc absent, and the tube itself is cylindrical with a circular 

 mouth. The ordinary compressed form of gullet often assumes, in 

 the position of rest, an cc -shaped transverse section, owing to 

 its walls coming together in the middle and leaving the two ends 

 wide open. In most of the Antipatharia the zooid is drawn out 

 in the direction of the long axis of the branch (Fig. 151), and in 

 some it becomes constricted into three parts {B) which may have 

 the appearance of separate zooids, the central part containing the 

 gullet with the mouth, while the lateral parts each contains a gonad; 

 each of these apparent zooids bears two of the six tentacles ; the 

 median one has all six mesenteries attached internally to the gullet; 

 in each lateral part there is only the outer portion of one of the 



