462 ECHINODERMATA ASTEROIDEA chap. 



is protected by plates covered with a mail of minute granules. 

 Pedicellariae of the valvate or alveolate type. Marginals large. 



Order 5. Forcipulata. — Asteroidea in which the dorsal 

 surface is beset with small spines surrounded by numerous for- 

 cipulate pedicellariae. Tube-feet with suckers and arranged in 

 four rows. Marginals rod-like and inconspicuous. 



Order I. Spinulosa. 



This is by far the most primitive order of Asteroidea. The 

 tube-feet are arranged in two rows only, and there is no special 

 means of protecting the back, other than the small close-set 

 plates bearing spines, with which it is covered. In some cases, 

 as Asterina, these spines have a tendency to converge when 

 irritated, and thus act somewhat like pedicellariae. This cir- 

 cumstance suggests strongly the manner in which pedicellariae 

 have been developed from small groups of spines. The order is 

 divided into six families, of which four have common represen- 

 tatives on the British coast. 



Fam. 1. Echinasteridae. — Spinulosa in which the aboral 

 skeleton is composed of close set plates bearing comparatively 

 small spines. This family is represented on the British coasts 

 by the beautiful scarlet Starfish Crihrella (ITenricia) sanguino- 

 lenta. It is also found On the Norwegian coast and- on the east 

 coast of North America. On the Pacific coast it is replaced by 

 a larger species, C. laeviuscula. The narrow ambulacral grooves 

 and sluggish movements at once distinguish it from the Starfish 

 described as the type. Indeed, all the Spinulosa seem to 

 be slow in their movements in contrast to the comparatively 

 active Asterias and its allies. Crihrella is remarkable for its 

 large eggs, which have a rapid development. The larva never 

 swims at the surface but glides only for a short time over 

 the bottom. Echinaster is an allied genus in which each 

 plate bears a single somewhat enlarged spine. It possesses 

 on the skin of the aboral surface numerous pits lined by 

 glandular walls, which probably secrete a poisonous fluid which 

 defends it. Acanthaster has thorny spines, more than ten arms, 

 and several stone-canals and madreporites. 



Fam. 2. Solasteridae. — Spinulosa in which the aboral skeleton 

 is a network of rods. Spines arranged in diverging bundles 



