182 



Figure 134: Strongylocentrotus intermedius. Pluteus III stage. 



b — basal rods. 



Remaining legend same as in Figure 109. 



ECHINARACHNIUS PARMA (LAMARCK) 



(Echinarachniidae) 



Mature eggs of this sand dollar species are encased in an envelope densely 

 speckled with crimson pigment granules. The eggs are 130—140 |im in di- 

 ameter and the membrane 60 fj.m thick. Development proceeds fairly rapidly. 

 The early pluteus stage is formed within 36 hrs after fertilization at a water 

 temperature of 20-21°C. 



Pluteus I Stage 



The larval body is short with a slightly tapering base. The body is 

 transparent, bluish, and devoid of pigment granules. Two pairs of arms de- 

 velop — the anterolateral and the postoral; the former is represented by simple 

 rods with short spines, while the latter contain complex perforations. From 

 the bases of these rods arise the inner transverse rods, which are connected 

 above the stomach and bear numerous small spines distally. The larval body 

 is supported by a pair of basal rods and a pair of secondary basal rods. All 

 these rods join in the basal part of the larval body; their distal ends are greatly 

 enlarged and form fenestrated plates, which are so tightly fused that traces of 

 their fusion are not visible in later stages. The secondary basal rods extend 

 to this plate and are likewise slightly enlarged at the site of connection. Such 



