86 COLOUR IN NATURE chap. 



corals belonged to it. The only other existing reef- 

 building Alcyonarian coral is Tubipora, the organ- 

 pipe coral ; here the coral itself is of a bright red 

 colour, and the polypes either brownish-red with 

 green-tipped tentacles, or entirely of a delicate green 

 colour. 



Colour - RESEMBLANCES in the Ccelentera 



We have already noted the plant-like habit of 

 growth which causes so many of the simpler Ccelentera 

 to be popularly mistaken for seaweed, but there are 

 also a few detailed resemblances which have been 

 described. Thus the species of the sea-anemone 

 genus Actinodendron have much-branched tentacles 

 which resemble the fronds of seaweeds or ferns very 

 closely. In the case of A. alcyonoideum the habitat 

 is in sandy pools in the corners of coral rocks ; the 

 long tentacles float freely in the water and sting with 

 extreme severity when touched ; the colour is dull and 

 seaweed-like. It is suggested by Saville Kent that 

 the resemblance to seaweed entices organisms within 

 the reach of the deadly tentacles, and that this is 

 therefore an example of " alluring coloration." A 

 species of a related genus [Megalactes griffithsi) has 

 tentacles of similar nature, and inhabits similar 

 situations, but is distinguished by a relatively elabo- 

 rate system of coloration, being marked by radiating 

 white lines on a ground of lilac, pale sea-green, 

 gray and buff. Again, in the species of Heierodactyla, 

 already mentioned for their elaborately beautiful fruit- 

 like nematospheres, the branched tentacles are grass- 

 green in colour and " present the aspect of aggregated 



