102 ANNULOIDA. 



The genus Corattium (including the living Red Coral) has 

 likewise been found in deposits of Miocene age. 



CHAPTER X. 



SUB-KINGDOM III. ANNULOIDA. 

 ECHINODERMA TA. 



SUB-KINGDOM III. ANNULOIDA. Animals in which the 

 alimentary canal is completely shut off from the general cavity of 

 the body. Nervous system distinct. A peculiar system of canals, 

 usually communicating with the exterior and containing water 

 derived from the outside, and termed the "water-vascular" or 

 " aquiferous" system, is present in all. In none is the body of the 

 adtilt composed of definite segments, or provided with " bilaterally 

 disposed successive pairs of appendages" 



This sub-kingdom was proposed by Huxley, as a provisional 

 arrangement, to include the two groups of the Echinodermata 

 (Sea-urchins, Star-fishes, &c.) and the Scolecida (Tape-worms, 

 Round-worms, Wheel-animalcules, &c.) Whether this arrange- 

 ment be ultimately retained or not, matters not at all to the 

 palaeontologist, as no member of the Scolecida is known in the 

 fossil condition. The palaeontologist, therefore, has simply to 

 deal with the Echinodermata, the complete distinctness of 

 which, as a group, is beyond question. 



CLASS ECHINODERMATA. 



The class Echinodermata comprises the animals known com- 

 monly as Sea-urchins, Star-fishes, Brittle-stars, Sea-lilies, and 

 Sea-cucumbers, and is distinguished by the fact that the external 

 envelope of the body (" perisome ") has the power of secreting 

 calcareous matter to a greater or less extent. The integument is, 

 therefore, either composed of calcareous plates articulated together, 

 or is coriaceous, and has granules or spicules of lime developed in 

 it. The water-vascular system usually communicates with the 

 exterior, and generally subserves locomotion. The adult animal 

 exhibits more or less distinctly a " radial symmetry" or star-like 

 arrangement of its parts, but the young animal is more or less 

 bilaterally symmetrical. 



The Echinodermata are divided into the following seven 

 orders : 



