XIV ZOANTHARIA CEKIANTHIDEA 409 



its allies dccurring in deep water are the forms regarded liy 

 Brook as dimorphic. 



Fig. 178. — A poition ot a linuch ot ixti/ ft]i s tn iHttmsis, showing three zooid.s and 

 the honn ixi-^ lies t ^^lth thuiii like inojections (Aftei Sthult/e. j 



Fam. 2. Leiopathidae. — This family includes the single 

 genus Leiopathes of the Mediterranean Sea. It is distinguished 

 from the others by the |)resence of twelve mesenteries. 



Fam. 3. Dendrobrachiidae. — This family also consists of a 

 single genus, Uendrohrachia, from 400 fathoms in the South 

 Atlantic. It is distinguished by having pinnate retractile 

 tentacles. 



Order VI. Cerianthidea. 



This order contains the remarkable Sea-anemone called Ceri- 

 anthiis. Two of the species have been placed in separate genera, 

 but they do not appear to be of more than sub-generic rank. 

 Cerianthus has a long cylindrical body with a double crown of 

 numerous long tentacles at the oral extremity and tapering to a 

 blunt point or rounded at the aboral extremity. 



There are numerous mesenteries, which increase in number by 

 the addition of bilateral pairs, arising only in the ventral 

 inter-mesenteric space throughout the greater part, if not the whole, 

 of the life of the zooid. The right mesentery of each young pair 

 is always more advanced than the left, so that the mesenteries 

 have the appearance of arising alternately right and left. None 

 of the mesenteries bear conspicuous bands of retractor muscles. 

 The movements of the body are effected by a thick band of 

 longitudinal fibres lying between the ectoderm and the mesogloea 

 in the body-wall. 



The absence or very slight development of muscles on the 

 mesenteries renders it difficult to recognise the homologues of the 

 protocnernes of other Zoantharia in the adult. From the 

 evidence of embryology, however, it seems certain that the six 

 dorsal pairs of mesenteries represent the protocnernes (Fig. 163, 3, 

 p. 368) and the others are metacnemes. 



