ECHINODERMATA. 277 



OPHIURAD^E. 



The Ophiuras are thus named from two Greek words (o0t9, a 

 serpent, and ovpa, a tail), from their fancied resemblance to the tail 

 of a serpent. These zoophytes are met with in almost every sea, but 

 chiefly in those of temperate regions ; they are very common on every 

 shore, and have been remarked by fishermen from the earliest times 

 on account of their singular form, the disposition of their arms, which 

 resemble the tail of a lizard, and by the singularity of their move- 

 ments. The general characteristics of this remarkable group of 

 Echinodermata, as described by Dujardin and Hupe, are as follows. 

 They are radiary marine animals creeping at the bottom of the sea, 

 or upon marine plants. In form they present a sort of coriaceous 

 disk, which is either bare or covered with scales, which contains 

 all the viscera, and five very flexible simple or branching arms, 

 each sustained by a series of vertebral internal pieces, naked or 

 covered with granules, scales, or bristles. Certain fleshy tentacula 

 thrown out laterally are organs of respiration. The mouth is situated 

 in the middle of the lower surface of the disk, and opens directly into 

 a stomach in the shape of a sac ; it is circumscribed by five re-entering 

 angles corresponding with the intervals of the arms, having a series of 

 calcareous pieces, which perform the function of jaw-bones. This 

 mouth is prolonged by five longitudinal clefts, garnished with papillae 

 or calcareous pieces, which correspond to one of the arms. A series of 

 calcareous pieces in the shape of vertebras spring from the extremity 

 of each of these clefts, which occupy all the interior of the arms, 

 having a furrow in the middle of the ventral surface for the reception 

 of a nursing vessel ; and laterally between their expansions are certain 

 cavities, from whence issue certain fleshy retractile tentacula; the 

 visceral cavity opens by one or two clefts on the ventral surface of 

 each side of the base of the arms. 



The Ophiuradse move themselves by briskly contracting their arms 

 so as to produce a succession of undulations analogous to those by 

 which a serpent creeps along. Some of these zoophytes are rather 

 active ; but others attach themselves by their arms to the branches of 

 certain other polyps, like the Gorgons, and remain immovable for a 

 considerable time, waiting their prey somewhat like a spider in the 

 midst of his web. 



