ANTHOZOA. ALCYONARIA 



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(fig. 39, ab) are placed in the corallites and give off 

 branching tubes (d) which cover the coenenchyma and 

 send blind prolongations or caeca (e) into its tubes. The 

 caeca were formerly regarded as siphonozooids. 



Fig. 39. Heliopora carulea. A single polyp and the adjacent soft parts. 



a, the projecting part of the polyp with eight pinnate tentacles ; 



b, lower part of the polyp ; c, ectoderm; d, sheet of canals; e, caeca. 

 (After Bourne.) 



Alcyonaria are rare as fossils, unless the Palaeozoic 

 genera, described below, be included in that group; but 

 the systematic position of those genera cannot yet be 

 regarded as definitely established. Some of them present 

 considerable resemblance to living Alcyonaria ; for example, 

 Si/ringopora is similar to Tubipora, and Heliolites to 

 Heliopora : on account of this, many authors maintain 

 that these fossil forms belong to the Alcyonaria, but this 

 relationship is denied by other writers who point out that 

 the skeleton is not formed of spicules, but is similar in 

 structure to that of Zoantharian corals, and further that 

 there is a close resemblance between Favosites and the 



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