284 CRUSTACEA ECHINODERMS, ETC. 



stars (so called from the readiness with which they 

 detach their arms when captured), we may there be- 

 hold Luidia fragilisissima (which has never been 

 kept healthily alive before), Ophiocoma, Ophiura, &c. 

 The " five-fingered " star-fish ( Ur aster rubens) is very 

 destructive to oysters, and may be seen in aquaria 

 devouring these delicious mollusca by insinuating 

 its bladder-like stomach between the two shells. 

 These, in some mysterious way, soon succumb to the 

 star-fish, and open as if the oyster were completely 

 paralysed ; so that the soft body is not long before it 

 becomes the prey of the persevering star-fish. 



The " sea-cucumbers " (Holothtiriadcz), as well as the 

 Sipunculida a group of marine transitionary worms, 

 intermediate in many respects between the annelids 

 and some of the Echinodermata are also represented 

 in most of our aquaria. 



The sea worms proper are very numerous. Some 

 of them are too rapacious to be kept, except by them- 

 selves, and do injury to the rest of the inhabitants of 

 the tank. Among these is the black Borlase's worm 

 (N enter tes Borlasii), several yards in length, which 

 stretches from one end of the tank to the other, like so 

 many foldings of ribbon. The Terebella is an interest- 

 ing object, half-way between naked worms and those 

 which live in limey tubes of their own secreting. The 

 Terebella simply forms an outer protection by cement- 

 ing grains of sand together, after the manner of a 

 caddis-worm. Serpulce (which may be seen in abun- 



