8 



A BIOLOGY OF CRUSTACEA 



Copepoda. Some typical copepodan forms are illustrated in figs. 

 7A-C. The Cyclopoida are almost monotonously alike, but it is 

 probably from this group that the majority of the parasitic forms 

 have evolved. The Calanoida are generally regarded as being 

 primitive; they have a heart, an organ not found in other copepods, 

 which are believed to have lost it during the course of their evolu- 

 tion. Of the non-parasitic groups, the Harpacticoidea show the 

 greatest range of form. Some are long and worm-shaped, others 



Table I. 



