50 ECHINODERMS OF THE BRITISH ISLES 



I. Order. Phanerozonia Sladen 



Marginal i:)lates well developed and usually conspicuous, 

 forming a distinct, mostly vertical margin along the edge of disk 

 and arms ; the oral and aboral side of disk and arms are thus 

 as a rule distinctly demarcated from each other. As a rule the 

 marginal plates are more or less covered by spines or granules, 

 sometimes, however, only by soft skin, in which case the plates 

 are less distinct. Papula? with a few exceptions (some Linckiidse) 

 confined to the aboral side (more rarely also between the 

 marginal plates). The aboral side covered with paxillae or 

 scattered spines, or it may be wholly naked. Pedicellariae, where 

 present, of the simple spiniform or pectinate or valvate type, 

 never of the crossed type ; they are found on the plates, never 

 attached to the skin by means of a soft stalk. Tube-feet always 

 in two series. With the exception of some species of Luidia, 

 normall}^ 5-TSiyed. 



The numerous forms of this, especially in tropical seas richly 

 represented, order of sea-stars are divided in three suborders. 



Key to the suborders of the Phanerozonia. 



1. Tube-feet pointed, without a sucking disk. Aboral side of disk 



and arms usually covered with paxillae . . I. Paxillosa 



Tube -feet provided with a sucking disk .... 2 



2. Upper and lower marginal plates alternating. Pedicellariae 



simple, spiniform, or pectiniform. Aboral side covered with 

 paxillse . . . . . . .II. Notomyota 



Upper and lower marginal plates not alternating. Pedicellariae, 

 when present, valvate or, more rarelj^ simple ; in the latter 

 case one or two large, recurved, hyaline spines on jaws. Aboral 

 side with paxillae, spines, or naked . . III. Valvata 



1. Suborder. Paxillosa Perrier. 



Dorsal side usually covered with paxillse, often with a central, 

 conical prominence. Marginal plates covered with spines of 

 varying length ; upper and lower marginals as a rule opposite 

 one another, not alternating. Simple, spiniform pedicellariae 

 may occur. Tube-feet pointed, without a sucking disk. No 

 paired dorsal arm-muscles. 



Three families are represented in the British seas. 



