204 PHYLUM ECHINODERMATA. 



Among preserved Ophiurids many specimens are found in 

 which the dorsal surface of the disc is absent.* The significance 

 of this fact is not understood. 



The larval form is the Ophiopluteusf (p. 140). In those forms 

 in which care of the brood occurs there is no free larva. The 

 ophiopluteus may present modifications in which the arms are 

 reduced. Such are Ophiopluteus metschnikoffi and daparedei. 

 The larvae known as Ophiopluteus annulatus,$ 0. krohnii, 0. 

 oblongus are vermiform, without ciliated band and without or 

 with only one skeletal rod. These larvae are pelagic. In- 

 cluding the vermiform larvae about seventeen ophioplutei are 

 known, most of which are as yet unrelated to any adult. 



The Ophiuroidea live upon the bottom of the sea and feed 

 upon the minute organisms and organic matter contained in 

 the surface mud, which they take up by means of the buccal 

 tube-feet. They move fairly actively by means of the lateral 

 flexion of their arms. In some forms the arms possess a power 

 of vertical movement as well, especially towards the end. When 

 the arms are very long they can be moved in a serpentine manner. 



The group first makes its appearance in the Upper Cambrian 

 (Ordovician). Its affinities are with the Asteroids, with which 

 it is sometimes united under the superclass Stelleroidea. It 

 is indeed difficult to separate them, especially when the palaeo- 

 zoic genera (Eophiura, Bohemura, etc.), recently described by 

 Jaekel, || and such a form as Astrophiura are considered. The 

 principal points of difference relate to the closing over of the 

 ambulacral groove (a feature which is but slightly marked in 



* Jeffrey Bell, in Gardiner's Maldive and Laccadive Expedition, 1903, 

 p. 223. Prof. MacBride states that he has seen an Amphiura squamata 

 throw off the whole dorsal surface of the disc with the stomach. 



f Mortensen, op. cit. 



j This is J. Miiller's vermiform asteroid larva, with segmented body 

 (Ueb. d. Larven u. d. Metamorphose d. Echinodermen, Abh. 3, p. 26, Abh. 

 d. Pr. Akad. d. Wiss. zu Berlin, Abh. i.-vii., 1846, 1848-53), and appar- 

 ently the larva described by Grave (Mem. Johns Hopkins, 1 900). The latter 

 is at first uniformly covered with cilia, which later become restricted to four 

 bands. These give it a resemblance to an Antedon larva, a resemblance 

 which is heightened by the fact that the last trace of the larval organ 

 (preoral lobe) is found at the edge of the aboral surface of the disc. The 

 author does not state whether this organ is encircled by the water- vascular 

 ring as it is in Asteroids. 



Preyer, Naples Mittheilungen, 7, 1886, p. 27. 



|| Asteriden und Ophiuriden aus dem Silur Bohmens, Zeitschr. der deut- 

 schen qeol. Ges., 55, 1903, p. 106. See also Bather's description of a 

 Devonian genus, Sympterura (Geol. Mag., 1905, p. 161.) 



