302 



NATURAL H1STOEY. 



SUB-ORDER ACTINARIA,. OR MALACODERMIC ZOANTHARIA. 



This sub-order has its members without any hard calcareous deposit in the mesoderm and 

 base, and the soft parts closely resemble those of the Stony Corals. In some instances there are 



calcareous spiculse in the tissues. 



'^^iii There are two families : the 



^n*ibj f Actinidse, with the tentacles in 



several alternating cycles, each 

 corresponding to a special peri- 

 gastric loculus ; and the Cerian- 

 thidse, whose tentacles are in 

 two concentric circles, so that 

 an inner and an outer tentacle 

 arise f fom the same perigastric 

 loculus, and their internal 

 cavities are continuous. The 

 mesenteries do not descend to 

 the bottom of the visceral 

 cavity, and the base of the 

 animal has not a fleshy sucker, 

 but the lower part is more or 

 less slender, and is placed in 

 the mud or sand. 



In the genus Cerianthus, 

 of this last family, the base is 

 perforated by a channel, opening 

 externally in a pore, and this 

 very exceptional structure in 

 the Actinozoa is for the purpose 

 of getting rid of undigested 

 matters. A kind of flexible 

 sheath is found around the 

 species, and is produced by an 

 aggregation of nematocysts cast 



forth by the skin. They are principally inhabitants of the Mediterranean, but a species was found 



at 2,780 fathoms in the Atlantic, and was described by Moseley. It was dwarfed, its anatomy was 



exceptional, and it was contained in a tube made up of the threads of its nematocysts. 



The great family of the A.ctinidae is subdivided into two groups. In one the bodies have a disc 



at their base or foot, and are more or less separate ; and in the 



other there are sclerites or hard spicuke in the tissues, which give a 



coriaceous texture to the mass. 



Amongst the first division are the Minyadinae, which do not 



fix themselves by their base or foot, but, by contracting it, form 



a more or less hollow space. Air is taken into this cavity, and 



the animal floats freely, with its tentacles and mouth downwards. 



The blue Minyas * of the Cape of Good Hope is melon-shaped, and 



flattened above and below ; it is blue, with white projections on it. 



Moseley described a floating form, with a cylindrical body and 



flattened base, which was obtained during the Challenger Expedition 



off the north-east of Australia, and one from 700 fathoms. The 



next division is that of the Actinina?, the great majority of which 



have an adherent base, which they can fix and unfix, and they have one kind of simple tentacles. 



At least twenty-four genera are included in this division, and there are a vast number ot 



* Mini/as coerulea. 



ANTIPATHES AUBOREA. 



VERTICAL SECTION OF SEA ANEMONE. 



a, month; t>, cavity of stomach ; c, body cavity : 

 a intermeseiiteric chamber: e, generative 

 filaments ; /, mesentery ; g, tentacle. 



