OPHIUROIDEA. 



207 



FIG. 146. Trickaster elegans 

 (after Ludwig). 



Order 4. CLADOPHIUEAE (EURYALAE). 



Gorgon-heads. 

 The ambulacral ossicles articulate with one 



another by means of hour glass-shaped surfaces 



and are covered by granular deposits in the 



thick integument. The arms may be simple or 



branched repeatedly. They can be moved 



in the vertical plane and 'coiled towards 



the mouth. There are no spines on the 



sides of the arms. Most of those with ion- 

 branched arms have a mouth-shield at the inner 



angle of each lower interbrachial space, one of 



which serves as the madreporite. Those with 



branched arms have often no mouth-shields, and 



the madreporites, sometimes single, sometimes 



five in number, are found in various regions of 



the lower interbrachial spaces. Pedicellaria-like 



processes are sometimes present. 



Fam. 1. Astro phytidae. With simple arms. 



Astrotoma Lym.* ; Astronyx M. andT.* ; Astro- 



chele Vll.* ; Astrogomphus Lym.f ; Astroporpa 



Orst. and Ltk.f; Ophiocreas Lym.| ; Astrocherna Oerst. and Ltk.J; Astro- 



ceras Lym.f. Brit. sp. : Astronyx loveni to 350 fms. 



Fam. 2. Trichasteridae. The arms branch a few times near their free 



ends. Trichaster L. Ag. (Fig. 146) ; 

 Astroclon Lym.; Astrocnida Lym. 

 Fam. 3. Euryalidae. The 

 arms branch much and from 

 near their base. Euryale Lmk. ; 

 Gorgonocephalus Leach (Fig. 

 147) ; Astropliyton Linck. Brit, 

 sp. : Gorgonocephalus lincM and 

 eucnemis. 



The genus Astrophiura Sladen 

 though undoubtedly an Ophi- 

 uran presents some Asteroid 

 features. The family Astro phiu- 

 ridae has been created for its 

 reception. The disc is penta- 

 gonal and the greater part of 

 the arms are included in it. The 

 free portion of the arms is short, 

 reduced and without tube-feet. 

 There are no teeth and the buc- 

 cal armature is simple and im- 

 perfect. Under arm-plates are 

 present and the cavities for the 

 retracted feet are spacious. The 

 madreporite appears to be ven- 



FIG. 147. Young Gorgonocephalus agassizi, 

 ventral view (after Lyman). 



tral. Madagascar and 

 neighbouring islands. 



the 



Disc large. 



Disc moderate (about one-tenth of length of arms). { Disc small. 



