167 



op 4 



QP 4 



op 5 



Figure 121: Aboral side of the young heart urchin Echinocardium cordatum. 



anp — anal plate; gp (1, 3, 4, 5) — genital plates; iam — interambulacral plates; m — 



madreporite; op (1, 2, 3, 4, 5) — ocular plates. 



(McBride, 1903; Ubisch, 1913; Onoda, 1931, 1936, 1938; Aiyar, 1936; 

 Kryuchova, 1979b). Primary podia do not form in the sand dollars (Kryuchova, 

 1979b). McBride (1903) noted many years ago that after the primary podia 

 had developed, the larvae of sea urchins of the genus Echinus begin to touch 

 the container well with them as though seeking an attachment site in order 

 to complete metamorphosis. 



The larvae of the sea urchin Strongylocentrotus purpuratus settle mostly 

 on coralline algae (Rowley, 1987). Cameron and Hinegardner (1974) identi- 

 fied the factors responsible for settling and demonstrated that for Lytechinus 

 pictus and Arbacia punctulata one of the factors was the bacterial film formed 

 on the walls of the containers holding larvae during metamorphosis. The 

 larvae of sea urchins generally prefer the bacterial-algal film common in the 

 sea as a substrate for settling (Chia et ai, 1984). Parechinus angulosus 



