EVOLUTION OF THE ECHINODERMS — FELL 



489 



Subclass Flexibilia 

 Subclass Inadunata 



Class Crinoidea 



Class Paracrinoidea 



Class Eocrinoidea " 



RADIAL GRADIENTS ACQUIRED 



RADIAL GRADENTS LACKING 



Subphylum Pelmatozoa 



Figure 18. — Classification of echinoderms based on growth gradient fields in postlarval 

 stages, as inferred from the evidence summarized in this paper. 



