80 COELENTERATA— ANTHOZOA phylum ii 



Subclass 1. TETRACORALLA Haeckel/ 



(Zoantharia Bugosa Milne Edwards ; PterocoralUa Freeh.) 



Extinct, Paleozoic, simple or composite scleroderm,ic corals, with septa arranged 

 according to a tetrameral system, and either hilaterally or radially symmetrical ; 

 without coenenchyma, hut with usually strongly developed endothecal tissue in the form 

 of tabulae or dissepiments, and with well-marked, frequently wrinkled epithecal wall. 



The Tetracoralla are especially characterised by having the septa, subse- 

 quent to the formation of the primaries, introduced along four lines rising 

 from the apex of the base of the corallum. The earlier stages of the Tetra- 

 coralla have recently been reinvestigated by Duerden, Carruthers and others. 

 Duerden concluded that the observations of Ludwig and Pourtales on the 

 primary hexamerism of these corals were correct. According to Carruthers, 

 in the developing young Tetracoralla the first stage of septal formation is for 

 a single septum to stretch entirely across the calice from wall to Avail. This 

 septum, which is called the axial septum, later breaks up to form the main 

 (cardinal) and the counter septum of the mature coral. In the next stage a 

 small septum appears on each side of the main septal end of the axial septum. 

 These two septa form the alar septa of the mature corallum. In the third 

 stage two other septa appear, one on each side of the counter septal end of the 

 axial system. After the formation of these six ^epta there is a distinct pause 

 in the formation of new septa and any irregularity in the dispos'ition of the 

 septa is corrected. Four of the six septa are called principal, and are con- 

 spicuous in the later septal arrangement ; these four are the main, counter, 

 and alar septa. Two of the first six septa, one on each side of the end of the 

 counter septum, are not so prominent in subsequent development. 



There is a controversy as to whether the primary septa of the Tetracoralla 

 are four or six in number : Duerden and Carruthers holding the number to be 

 six, while Brown and Gordon contend that it is four. The four principal septa 

 are sometimes of equal proportions, when they may be either stouter and 

 longer than the others (Stauria), or thinner and shorter (Omphyma) ; or they 

 may be of unequal proportions. Of the two principal septa which lie in the 

 longitudinal axis of the corallum, one (called the main or cardinal septum) is 

 frequently situated in a depression or furrow known as t\iQ fossula (Fig. 100) ; 

 while the other or counter septum is either normally developed, or is more or 

 less reduced. Occasionally the counter septum is placed in a fossula, while 

 the cardinal septum is normally developed ; but the two laterally disposed or 

 alar septa are always equal in size. The remaining septa not infrequently 

 exhibit a well-marked radial arrangement, in which the longer and more 

 strongly developed usually alternate with the shorter and less strongly 

 developed. New septa, according to Kunth and Dybowski, are inserted in 

 the following order. First, a new septum is given off on either side of the 



1 Tjiterature : Kunth, A., Beitriige zur Kenntniss fossiler Koralleii. Zeitschr. deutscli. geol. 

 Ges., 1869-70, vols, xxi., xxii. — Dyhowski, W. N., Monograpliie tier Zoantharia Rugosa, etc. Archiv 

 fiir Naturkunde Liv-, Est-, imd Kurlands, 1874, vol. v. — Roemer, F., Lethaea Palaeozoica, 1883, 

 pp. 324-416. — &chliHcr, Clem., Antliozoeu des rlieinischen Mittel-Devons. Aljluuidl. preuss. geol. 

 Landes-Aiistalt, 1889, vol. viii. — Brown, T., Studies ou the Morphology and Development of certain 

 Rugose Corals. Ann. N.Y. Acad. Sci., 1909, vol. xix. — Faurot, L., Affinites des Tetracoralliaires 

 et des Hexacoralliaires. Annales de Palcont., 1909, vol. iv. 



