OPHIUROIDEA 



23' 



of the arm. These very characteristic grooves are, in younger 

 specimens, distinct only in the proximal part of the arm, in larger 

 specimens somewhat farther out. Three to four tentacle scales in 

 the proximal part of arm, farther out 2 and distally only 1 . At the 

 innermost {i.e. second-third) pore pairs there are 2-3 broader 

 papillae on the outer edge of the pore, at the following 2-3 pairs 

 only 1. Of the three arm spines the lowermost, which is placed 

 close to the tentacle scales, is the shortest, only little longer than 

 the tentacle scales ; the second is the longest, about the length 

 of an arm joint. The spines are placed at equal distances from 

 one another. Mouth shields about twice as long as the distance 

 from their outer edge to the edge of disk. Four to six pointed 

 mouth papillae. Colour in life reddish or reddish -brown, often 



Fig. 129. 



-Larva (Ophiopluteus) of Ophiura texturata. 

 (From DanmarFs Fauna.) 



ca. 25. 



somewhat spotted. Oral side yellowish or white. Reaches a size 

 of ca. 35 mm. diameter of disk ; arms ca. three and a half times 

 as long as the diameter of disk. 



The larva (Fig. 129) differs from all other Ophiuroid larvae 

 known till now, in having fenestrated rods in the postero- 

 lateral arms. It may be found throughout most of the summer. 

 The young brittle-star reaches sexual maturity in its third year, 

 at a size of 7-11 mm. diameter of disk. The very large specimens 

 of ca. 30 mm. diameter of disk are probably 5-6 years old. 



A parasitic Copepod, Parartotrogus Richardi Scott, of the 

 family Asterocheridae, appears to infest this Ophiurid (it has, 

 however, not yet been directly observed to infest it). In the 

 Limfjord, jiutland, where this Ophiurid occurs in great numbers, 

 it is often infested with a small parasitic green alga, Coccomyxa 

 ophiurcB Rosenvinge, which dissolves the calcareous skeleton 

 and probably in the end kills the animal, like a sort of cancer. 



