296 



COMPA RA TIVE ANA TOMY 



CHAP. 



Sub-Class 2. Euasteroidea. 

 Asteroidea with paired, i.e. opposite ambulacral plates or "vertebra;." 



Order 1. Phanerozonia. 



Asteroidea with large, strongly developed, marginal plates. The inframarginal 

 and supramarginal plates are closely fitted together. Papulfe (brancliial vesicles) 

 only occur on that surface of the body which is surrounded by the supramarginal 



«'<t^. 





Fio. 230.— Ctenodiscus procurator (after Sladen), from the oral side. A Gastropod in llie 

 stomach is visible through the mouth. 



plates, i.e. on the apical or upper side. Ambulacral jilates broad. In each ambu- 

 lacral furrow there are two longitudinal rows of tube-feet. The adambulacral plates 

 are prominent in the oral skeleton. Where pedicellaria; occur they are sessile. 



Fam. 1. Archasteridse : Pararchastcr, Dytaster, Plutonaster, Pseudarchastcr, 

 Arclmstcr, etc. Fam. 2. Porcellanasteridae, the centre of the apical system pro- 

 duced into a more or less long outgrowth : PorceUanaster, Huphahisfcr, Ctcnodhcvs 

 (Fig. 239), etc. Fam. 3. Astropectinidse, without anus and usually without pedicel- 

 lariae : Astropecten, Bathyhiastcr, Ibjastcr, Luidia, etc. Fam. 4. Pentagonasteridse : 

 Pentagoimskr, Astrogonium, Nedria, Calliaster, Stellastcr, Goniodiscus, Muaastcr, etc. 

 Fam. 5. Antheneidse : Antheiwa (Fig. 240), Guniastcr, etc. Fam. 6. Pentacerotidse : 



