Echinoderms. G5 



Like some of the Sea-urchins, most Sea-cucumbers live by swallowing 

 sand and mud and digesting the adhering organic particles. Some (e. g. 

 Cucumaria. Fig. 100; manage matters very differently. They remain 

 motionless on a stone or 

 other prominent object , 

 stretching out their large 

 branching tentacles and 

 carrying them one after 

 the other in their mouth, 

 sucking off the small ani- 

 mals which in the meanti- 

 me have settled upon them. 

 With a little patience this 

 proceeding may be easily Fig. 160. Cucumaria Hand, 1 ! 2 nat. size. 



observed. Some Sea-ur- 

 chins (e. g. Dorocidaris. Fig. 7) have very long sp'nes; in these cases, 

 however, the sucker-feet can be extended to great length, for they must 

 always reach beyond the spines. In many cases we find between the 

 spines special moveable stalks bearing small pincers, which can also seize 

 small objects. The Starfishes have their eyes at the extremities of their 

 arms. They can, however, probably not see very distinctly, b.it only di- 

 stinguish between light and darkness. 



The Echinoderms are divided into four large groups: 



1. The Feather-stars (Crinoidea). 2. the Sea stars (AsteroideaX 3. the 

 Sea-urchins (Echinoidea), 4. the Sea- cucumbers (Holothurioidea). 



Of the Feather-stars the Aquarium contains Antedon rosacea (Fig. 6) 

 in straw-coloured, orange-coloured, blood-red, or spotted brown and white 

 varieties. Generally they hold on to coral-branches, so as to appear like 

 flowers, growing on submarine trees. 



The Sea-stars are divided into the Starfishes or Asterids and the 

 Brittle-stars or Ophiurids. The Starfishes are represented in the Aqua- 

 rium by the genera Luidia (Fig. 5), Astropecten (Fig. 1) Asterias 

 (Fig. 3), Echinaster (Fig. 2), Palmipes. and others; the Brittle-stars 

 by Ophioderma (Fig. 4) and others. 



The Sea-urchins are very conspicuous : Echinus acutUS especially 

 on account of its considerable size. The large yellow ovaries (roe) of 

 StrotlgylocentrotUS and allied species are eaten in the fish-market raw 

 as we eat oysters. SpaerechimiS (Fig. 8) is of a beautiful violet or 

 reddish-brown colour; and Dorocidaris (Fig. 7) is remarkable on account 

 of the size and thickness of its spines, which are few in number. 



The Sea-cucumbers are very common in the Bay of Naples , and 

 the Aquarium contains about half a dozen kinds; among others the brown 

 Holothuria tubulosa (Fig. 10) , attaining the length of one foot; and 

 Stichopus (Fig. 11), which is not round but flattened. Both of these 

 are very remarkable for containing frequently within their body a fish. 

 Fierasfer acus, 8 to 10 inches long, which at times may be seen pro- 

 truding its head from the anus of its host. It feeds on small crabs, but 

 to catch these it is obliged to leave its shelter. Some kinds of Sea-cu- 

 cumbers are considered a great delicacy by the Chinese: what they call 



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