OPHIUROIDEA 155 



11. Transverse rods large, branched, serrate (Fig, 87, 2) 



Ophiopluteus ramosus Mrtsn. 



Transverse rods very short, only with a pair of small branches 



at the end (Fig. 113) . . . . . Ophiactis Balli 



12. Postero -lateral arms well developed; body-skeleton fairly com- 



plete (Fig. 133) Ophiura affuiis {t) 



Postero -lateral arms not developed ; skeleton quite rudimen- 

 tary (Fig. 89) . . . Ophiopluteus Claparedei Mrtsn. 



Fig. 89. — Ophiopluteus Claparedei. Enlarged. (After Claparede ; from 

 Th. Mortensen, Developm. and larval forms of Echinod.) 



Besides the larval forms enumerated in this key there is a 

 possibility that Ophiopluteus himaculatus (Joh. Miiller) may also 

 occur in the British seas, this Mediterranean larva having been 

 found also off the Moroccan coast, do^vn to the Cape Verde 

 Islands. It belongs to the group of larvae wdth composite body 

 skeleton, but is distinguished from Ophiopluteus ramosus in 

 having simple transverse rods and from the Ophiactis Balli larva 

 in having a process from the transverse rods (median rod) ; it is 

 further characterised by having a pair of black spots in the basal 

 part of the body. It is unknown to which Ophiuroid this larva 

 belongs. 



Regarding the Ophiopluteus species named above, there is 

 some reason for supposing that Ophiopluteus dubius may perhaps 

 belong to Amphiura Chiajei, Ophiopluteus compressus to Ophiura 

 Sarsi, whereas no suggestion can be given at present as to 

 which Ophiuroids the larvae Ophiopluteus coronatus, ramosus, and 

 Claparedei belong. 



The classification of the brittle-stars is not j-et definitely 

 settled. A much-used classification is that of Bell, dividing them 

 according to the type of vertebral articulation into AstrojMurce 

 or Cladophiurce, with hour-glass-shaped articular surfaces, the 

 Streptophiurce, with a simple ball-and-socket joint as vertebral 



