ECHINOIDEA 



The Tripneustes gratilla is by far the most common of this 

 group. It is a typical tropical sea-urchin, dark or black in 

 colour, its spines from eight to ten inches long, as frequent 

 in coral depths as along the rocks and found even in ports 

 on the sides of the wharves. One of the inconveniences facing 

 those who repeatedly enter these waters is being stuck by 

 these urchins. Such an encounter is painful because it is 

 difficult to extract the spines from the flesh. Fortunately, the 

 acute initial pain soon passes, and there are no further 

 consequences. Another urchin, the Prionocidaris baculosa with 

 not so many but rather bigger spikes, is common in the 

 Dahlaks and in regions further north. The Heterocentrotus 

 mammillatus has the most impressive spines of all, as big as 

 or bigger than a normal pencil. One of the characteristics of 

 these spines is their power of growing a new tip when one is 

 broken. Finally, the Olypeaster is often found on sands. It is 

 very flat with a thick down of stiff spines and in some species 

 the perimeter is almost pentagonal. 



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