MARINE BIOLOGICAL STATION AT PORT ERIN. 



79 



ECHINODERMATA. 



(Figs. TIL and VIII.) 



Star-fishes, Sand-stars, Brittle-stars, Feather-stars, 

 Sea-urchins and Sea-cucumbers are all characterised by 

 having plates and spicules of lime in the skin which may 

 project from the surface as spines. Hence they are known 

 as " prickly-skinned " animals (Echinodermata). They 

 also have as another important characteristic a remarkable 

 system of tubes containing a watery fluid, parts of which 



Fig. VII. 



can be protruded as suckers for locomotion. These suck- 

 ing tubes can be seen acting as feet in star-fishes or sea- 

 urchins creeping up the glass of an aquarium. In the 

 Echinus shown at 5 (fig. VIII.) the short straight pointed 

 projections are calcareous spines, and the longer flexible 

 bodies are tube-feet, with suckers at their ends. 



