The Life History and Post Embryonic Development of the Copepods, Calanus tonsus Brady and Euchaeta japonica Marukawa

Abstract

Calanus tonsus Brady is an abundant, deep water species in the strait of Georgia. Development is characterized by a distinct metamorphosis and the six nauplius and six copepodid stages are described. The life cycle extends over one year and breeding occurs in the spring at the surface. The nauplii and early copepodid stages are soon replaced by stage V which dominates the plankton from May to December. C. tonsus exists as an adult for approximately two months—January and February. Maturity is accompanied by marked degeneration of the mouth parts in both sexes, death following shortly. The retrograde development appears associated with a change in habits. Stage V stores up reserve food, and the mature females with the disappearance of feeding devices depend upon this accumulated food during the reproductive period. Euchaeta japonica Marukawa occurs in limited numbers in the deep water of the strait of Georgia. It undergoes a similar metamorphosis to C. tonsus and the twelve stages are described. There is no definite spawning period but reproduction occurs throughout the year in deep water where development proceeds. Several broods may be produced by one female but the males are believed to die shortly after copulation. The nauplii differ from those of C. tonsus due to larger size, slight increase in length from stage I to stage VI and retarded development of the appendages. The conspicuous feature of the copepodid development is the extreme degeneration of the male mouth parts.