Echinodenns. 



65 



Fig. 161. Cucinnaria Planci, '/a nat. size. 



contains. The Stavfislies liavc no tcctli, l)ul the walls of their alimentary 

 canal secrete such strong juices that they can kill animals Avhich they 

 have caught with their sucker-feet and brought to their mouth. Their 

 food consists chiefly of shellfish, but often they will capture fishes and 

 crabs. They are one of the most formidable enemies of fishery, especially 

 of oyster-culture. 



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

 lowing sand and mud and digesting the adhering organic particles. Some 

 (e. g. Cueumaria, Fig. 161) manage matters very differently. They remain 

 motionless on a stone 

 or other prominent ob- 

 ject, stretching out their 

 large branching tentac- 

 les and carrying them 

 one after the other into 

 their mouth, sucking off 

 the small animals whicli '(t^if 

 in the meantime have 

 settled upon them. With 

 a little patience this 

 proceeding maybe easily 



observed. — Some Sea-urchins (e. g. Doroeidaris, Fig. 7) have very 

 long" spines ; 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 tiielr arms. They can, however, probably not 

 see very distinctly, but only distinguish between light and darkness. 



The Echinoderms are divided into four large groups: 



1, Tlie Feather-stars (Crinoidea), 2. the Sea-stars (Asteroidea), 3. the 

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



Of tlie 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 \\\\(> the Starfishes or Asterids, and the 

 Brittle-stars or Ophiurids. The Starfisiies are represented in the Aquarium 

 by Mic genera Luldia (Fig. .^)), Astropeeten (Fig. 1), Asterias (Fig. 3), 

 Eehinaster (Fig. 2), Palmipes, and others; the Brittle-stars by Ophio- 

 derma (Fig. 4) and otiiers. 



The Sea-urchins are very conspicuous ; Echinus acutus especially 

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

 Strong-yloeentPOtus and allied sjiecies are eaten in the fish-market raw 

 as we eat oysters. Sphaerechinus (Fig. 8) is of a beaiitiful violet or 

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

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



The Sea-cucumbers are very comn;on in the Bay of Naples , and 

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

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



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