ECHINODERMS 6j 



The Brittle Stars (Opkiocoma) are not unlike the Sand 

 Stars, but the arms are much longer and are densely fringed 

 with needle-pointed spines. Our largest species, O. niger, 

 shows a most wonderful diversity of colouring and pattern, 

 scarcely two specimens being found exactly alike. These 

 and the Sand Stars part with their arms on the slightest 

 provocation. 



Most striking of all the Starfishes are the Basket Stars 

 (Euryalida), abundant in most seas at almost any depth 

 below the ioo fathom line. The typical five rays are 

 divided and subdivided until they give rise to thousands 

 of terminal branches. The Basket Star walks upon the 

 tips of these branches seeking its prey, and food not in- 

 frequently comes to it in the form of fishes who seek 

 shelter amongst the tangled arms, mistaking them for 

 weed thickets. 



At first glance a Sea Urchin has little in common with 

 any of the creatures just described. Examination shows, 

 however, that it is built upon the five-rayed pattern and 

 that although the animal is encased in a flattened or spherical 

 shell, this is pierced by numerous holes, through which 

 tube feet are thrust, by means of which the creature pro- 

 gresses at an even pace over horizontal or vertical surfaces 

 with equal facility. In addition to the features shared 

 with the starfishes and Sea Cucumbers, Sea Urchins 

 differ in several important points. Besides the tube feet, 

 the outer shell or test is usually provided with numerous 

 spines often of great length and either sharply pointed 

 or club-shaped. These spines are each mounted on a ball 

 and socket joint and can be moved within a certain radius, 



