OPHIUROIDEA 633 



FAMILY 7. BBISINGIDAE. 



Disc small and circular ; arms 8 to 18 in number, long and round and 

 set off from the disc like those of brittle-stars ; feet in 2 rows ; numerous 

 pedicellariae : 6 genera, all of the species of which live in the deep sea. 



ODINIA Perrier. Disc with papulae on the upper surface ; arms very 

 fragile: 6 to 8 species. 



0. americana (Verrill). Rays 20 in number, about 35 cm. long; 

 color bright orarige-red : New England coast, in 175 to 400 fathoms ; rare. 



CLASS 3. OPHIUROIDEA.* 



Brittle-stars. The brittle-stars resemble the starfish in form, but 

 the five rays are greatly elongated and form slender, cylindrical arms, 

 which are sharply set off from the central disc and possess no ambulacral 

 groove. Two rows of ambulacral appendages project from their oral 

 surface into the water, but these lack terminal suckers and hence are not 

 locomotory organs: the animal progresses by the snake-like movements 

 of its arms. As in the starfish, the oral sur- 

 face, with the mouth in its middle, is di- 

 rected downwards, and the main body axis 

 is very short. The mouth is a complex star- 

 shaped opening bounded by characteristic 

 skeletal pieces (Fig. 983) ; an anus is not 

 present. The madreporite (3) is in the 

 oral wall in an interradius. At the base of 

 each arm is a pair of slits (1) which open 

 into a pair of pouches called the genital 



bursae ; in Ophioderma each slit is in two pig. 983 Oral surface of the 



, ml ., t . disc and the base of the arms 



parts. These organs are possibly respiratory (Coe). i, genital bursa ; 2, 



f> , 3 i ,1 i n mouth; 3, madreporite; 4, 



in junction and are also the receptacles of arm spine- 5 buccal plate- 6 



the genital products. 3aw ; 7 ' ral papillae ' 



The external surface is not ciliated; pedicellariae are not present; 

 spines usually project from the sides of the arms, and spines, scales, or 

 granules are present on the disc. No special sense organs are present. 

 In most species the number of arms is five, but there are six normally 

 in some, and in others, seven or eight. In most of the Astrophytidae 

 they are more or less branched. 



Internal Structure. The calcareous skeleton is usually well devel- 

 oped. The upper wall of the disc is flexible and contains a large num- 



* See "Report on the Ophiuroidea," by T. Lyman, Challenger Reports, Vol. 5, 1876. 

 "Ophiuroidea," by H. Ludwig and O. Hamann, Bronn's Tierreich, Vol. 2, 1901. "The 

 Ophiurans of the San Diego Region," by J. P. McClendon, U. of Cal. Pub., Vol. 6, 1909. 



