CCELENTERATA — CORALS 



131 



Derivation of name. — Anthozoa > Greek anthos, flower, + 

 zoon^ animal ; in reference to the flower-like appearance of the 

 expanded polyp, especially of the more brilliantly colored tropi- 

 cal species, the tentacles corresponding to the petals, and the 

 region about the mouth to the disk. 



The Anthozoa are subdivided into the following sub-classes 

 and super-orders : — 



Page 



1. Zoantharia 131 



a. Tetracoralla (Tetraseptata) 131 



h. Hexacoralla (Hexaseptata) 133 



2. Alcyonaria 135 



a. Octocoralla (Octoseptata) 135 



h. Tabulata (Aseptata) 136 



Sub-class i, Zoantharia 



Tentacles usually hollow and simple, never pinnate ; they are 

 four to six, or more than eight in number, with a usually equal 

 number of mesenteries and septa. 



Skeleton present or absent ; when present it is developed by 

 the ectoderm and may be horny or calca- 

 reous, but is never in the form of scattered ^j^^^^-^- 

 spicules. 



Super-order a, Tetracoralla 



Simple or composite corals with septa 

 in quadrants (whence the name from 

 Greek tetra-, four). Corallum calcareous. 

 Entirely extinct, known from the Ordovi- 

 cian to the Permian. 



Microcyclas (Fig. 48). Devonian. 



Simple, disk-shaped (whence the name 

 from Greek mikros, small, -t- cyclos, circle). 

 It consists merely of a calcareous plate 

 with ridge-like septa and a fossula. 



Fig. 48. — A simple coral, 

 Microcyclas discus Meek 

 and Worthen, from the 

 Hamilton (Middle De- 

 vonian) of Illinois, fos., 

 fossula; sep., septum. 

 Natural size. (Redrawn 

 from Meek and Wor- 

 then.) 



