172 



CORALS 



Cellaria. — The genus Cellaria (Fig. 84) must be briefly 

 referred to, partly because it includes a very common and 

 widespread species and partly because it affords us another 

 example of a jointed colony, calcareous internodes being 

 connected together by tubular horny nodes. 



Cellaria fistulosa is one of the commonest of the British 

 corallines, extending from shallow to deep water in many 

 localities off our own coast, but has also been recorded in 



the Indian Ocean, off New 

 Zealand, Australia, the Cape 

 of Good Hope, and other 

 distant places, so that it 

 may be regarded as a 

 cosmopolitan species. 



It forms typical little 

 coralline tufts or shrubs 

 some two or three inches 

 in height, attached to 

 rocks or shells, consisting 

 of numerous cylindrical and 

 jointed branches dividing 

 dichotomouslyat the nodes. 

 The internodes are calcar- 

 eous and are formed by a 

 large number of zooecia 

 arranged usually in longi- 

 tudinal rows. They are, 

 of course, very variable in 

 size, but in a typical speci- 

 men, say from the Firth of 

 Clyde, the internodes may be found to have a length of 

 10 mm. and a diameter of 0-5 mm. The horny nodes are 

 very short, o-i mm. in length, but quite sufficient to give the 

 colony the necessary flexibility to yield without breaking to 

 the movement of tides and currents. 



In the description that has been given in the preceding 

 pages of a few representative genera of calcareous Polvzoa, 

 some idea may be gained of the range of form and structure 

 of coralline skeleton found in this group. It ma\' also serve 



Fig. 84. — Cellaria fistulosa. Firth of 

 Clyde. The specimen on the left drawn 

 to iiat. size. 



