XIII 



ALCYONARIA STOLONIFERA 



343 



Sarcodictyon is found in depths of 10 to 22 fathoms in the Irish 

 Sea, off the west coast of Scotland, the Shetlands, and off the 

 Eddystone Lighthouse, South Devon. 



Another very important genus is Tubipora, in which the 

 tubular body-wall of each zooid is very much longer in proportion 

 to its diameter than it is in Sarcodictyon, and the anthocodia is 

 retracted not into the stolon, but 

 into the basal part of the body- 

 wall. The zooids are connected 

 together by horizontal platforms 

 on which new zooids are formed by 

 gemmation. Both horizontal plat- 

 forms and the body-walls of the 

 zooids are provided with a skeleton 

 of fused spicules of a red colour. 



This genus is the well-known 

 Organ-pipe coral, and is found some- 

 times in immense quantities on the 

 coral reefs of both the old and new 

 world. 



It may be seen in pools on the 

 edge of the reefs at low tides in 

 colonies frequently a foot or more 

 in diameter. The tentacles are 

 often of a bright emerald green colour, and as the anthocodiae 

 stand expanded in the clear water they contribute a brilliant 

 patch of colour to the many beauties of their surround- 

 ings. When the coral is disturbed, or the water shallows 

 and the anthocodiae are retracted, the dull red colour of the 

 skeleton gradually takes the place of the bright green of the 

 tentacles. 



It is probable that this order of Alcyonaria was better repre- 

 sented on the reefs of some of the earlier periods of the world's 

 history than it is at present. The fossil Syringopora, which is 

 found abundantly in the carboniferous limestone and other 

 strata, was probably an Alcyonarian belonging to this order. It 

 resembles Tubipora in its mode of growth, but in place of the 

 horizontal platforms connecting the zooids there are rods or bars 

 from which new zooids spring (Fig. 152). Similar connecting 

 bars are found in the recent Clavularia (Ricksonia, Delage) 



Fig. 151. Tubipora mtisica, a young 

 colony growing on a dead Madre- 

 pore branch (M). Up, The con- 

 necting horizontal platforms ; p, p, 

 the skeletal tubes of the zooids ; 

 St, the basal stolon. 



