66 Animal Life by the Sea-shore. 



VII.— POLYPS, JELLY-FISHES AND 



SPONGES. 



This last chapter deals witli a number of lowly organised 

 animals, which, on account of their radial sj^mmetry, were once 

 grouped together with the Echinoderms in the large division 

 Radiata. They are now placed in two separate divisions, the 

 Coelenterates (Potyps and Jelly-fishes) and the Porifera 

 (Sponges). All these forms differ from the Echinoderms, and 

 the representatives of the other higher groups, in not having 

 a specialised alimentarj' tube, the single cavity contained 

 within them subserving all the functions and acting as gut, 

 circulatory system, etc. ; sometimes even as a brood pouch. 

 The most familiar Pol3'ps are undoubtedly the Sea-anemones, 

 also the largest and, owing to their great beauty of form and 

 their vivid and varied tints, among the most attractive of our 

 seashore animals. 



Commonest on all parts of our coasts is the Smooth Anemone 

 or Beadlet, Actinia mesembryanthemum (Fig. 79), which furnishes 

 a good example for studj'. The organisation is of a very simple 

 type, the animal, when e,\panded, presenting ^ the form of a 

 cylinder, attached at the base and containing a cavity which 

 communicates \vith the exterior b}- an oval mouth opening in 

 the centre of the free extremity'. Surrounding the latter are 

 the mobile tentacles, used for the capture of food, and provided 

 with peculiar stinging or urticating organs which, like those of 

 the jelly-fishes, form a powerful offensive and defensive apparatus. 

 The tentacles can be completely retracted, and the animal, 

 when molested, or when exposed out of the water at low 

 tide, can contract to such an extent as to form an incon- 

 spicuous, fleshy knob. This anemone is very variable in 

 colour ; although usually dark red, green and brown varieties 

 occur ; the tentacles are of a lighter tint than the body. The 

 species can be recognised by the smoothness of the body and by 

 the presence of a ring of bright blue, bead-like tubercles below 

 the whorls of tentacles. 



The allied Anthea cereus (the Opelet), common in deep 

 rock-pools, also has a smooth body, but differs from the BeacUct 



