ECHINODEKMATA. 



Disk entire, with five or more arms .... 

 Disk lobed or pentagonal 



43 



OPHIUROIDEA. 

 ASTEROIDEA. 



Order I. OPHIUKOIDEA. 



Disk entire, containing all the -viscera, and giving off five or 

 more slender arms, not channelled beneath. Tube-feet without 

 suckers. 



The arms are not prolongations of the disk, and are not chan- 

 nelled beneath, as in Asteroidea ; they are each enclosed in four 

 rows of calcareous plates, and, having no suckers, these arms are 

 their only means of locomotion. There are no pedicellariae. The 

 madreporiform tubercle is inferior, near the mouth. 



J. Muller has two divisions Ophiureae with simple, and Eu- 

 ryaleas with branched arms ; the latter is confined to the family 

 Astrophytidse. The former are known as " sand-stars." Our com- 

 moner British species are Ophioglypha lacertosa, Ophiura lavis, 

 Ophiothrix rosula, and Amphiura sguamata [= Ophiocoma neglecta, 

 Johnst.]. 



Astrophiuridce. 

 Astrophiura. 



Order II. ASTEEOIDEA. (Starfishes.) 



Disk more or less lobed or pentagonal, the lobes continuous 

 with the disk, hollow, and receiving prolongations of the viscera. 

 Tube-feet with suckers. 



The lobes are channelled beneath for the ambulacral feet or 

 suckers, which act as organs of locomotion. The madreporiform 

 tubercle is on the back ; a curved calcareous canal connects it 

 with the mouth. Sometimes five tubercles are present, and as 

 many canals. Pedicellariae occur on the body or on the mouth. 



