230 



CCELKNTERATA 

 Order I. Tetracoralla (Rugosa). 



Exlinct f(irms frcim the palco/oic rocks willi llic parls arranged in fours (hg. 

 196, I). The present lemleney is to regard them as modilied llexacoralhi. 



Order II. Octocoralla (Alcyonaria). 



These forms, whicli Iiaxe eiglit single septa, are reeogni/.able by their eight 

 featliered tentacles (lig. 107). They occur in all si-is fnmi near (he shore to great 

 depths. In development there is a plannla (fig. joi) in which the cy.sophagiis 

 arises as a solid ingrowth which becomes perforated later. The eiglit septa 

 arise simultaneousiv. I'sually colonii'S are formed by budding and a poly- 

 morphism may occur, some indixiduals which lun'e reduced septa and hick 

 tentacles, taking in water for the colony. Many are phosphorescent. 



Fig. 201. Fio. 202. 



Fio. 201. — Tlirce stages in development of Riitilla roiifonnis (after \\'ilson). 

 A, cleavage of egg; B, jilanula; C, de\elopnient of a'sopliagus; cc, ectoderm; cti. ento- 

 derm; /;/, nieso^L^lcTa ; 0, a-soplia^^iis. 



l'"ic.. 202. — .Vmerican sea-aiieniones. .1, KtkvardsiclUi si piiut-iiloiiJcs (after Slini]i- 

 son). B, BiciJiiiiii parasiliiiiiii (after \'crrill). i', Biiinnhs slclla iafler XerrilO. 



.\LrYONiiD.T; {Ah-youiuiii'''), axial skeleton is lacking, the llesh contains 

 numerous calcareous particles (sitcrodcniiilfi). The sea pens, rtcNX.-VTiM.m.-v;, 

 have the basal part buried in the mud, the rest, expanded like a disc or feather, 

 l)ears the ]iolyps. An axial skeleton usually occurs in the stalk. PiinnUidii* 

 Rciiill(i'''\ riic GoRGONiiD.E (sea fans, sea whips) liaxe an axis of more firm- 

 ness, which may be calcareous, and the colonv niav branch and the branches 

 anastomose. Here belongs, besides nianv tropic;il gener;i whose names end in 

 'i^orgia,' the jn-ecious coral (Cori)lliiiiit nihrmii, hg. 11)7), the iishing for which at 

 Naples amounts yearlv to li;df a million dolhirs. 'i'luut'ORin.-K, orgaii-|iipc 

 corals. The Heliopokid.ic were long regarded as llexacoralla because of their 

 ma.ssive skeletons with six sclerosepta. The paleozoic Syrini^ofiinui belongs 

 near Tubipora, while the 1*"a\'OSITid.e resemble the .Mcyoniidx. 



Order III. He.xacoralla (Zoantharia). 



The simple tubular ten(;icles are highly characteristic of the llexacoralla, 

 as is the arrangement of the p;Lired septa in sixes as described abo\'e. ^'et there 

 are exceptions to this rule. On the one hand is AVicij/i/i/u* with sixteen or 



