Description of the developmental stages in Acartia bifilosa Giesbrecht (Copepoda: Calanoida)

The developmental stages and increase in length of Acartia bifilosa, a dominant planktonic copepod in Kyeonggi Bay, Yellow Sea, Korea, were investigated in a laboratory. Adults laid eggs at a rate of 2.5 eggs day1 female*1 and up to 97% of eggs hatched. The eggs were 92 jim in diameter and larger than the eggs of other Acartia species. The body segmentation was recognizable at the fifth nauplius stage and sex distinction was possible at the fourth copepodite stage. The six nauplius stages took -7.5 days and the five copepodite stages -8.5 days. Sexually mature males and females appeared at the 16th day, and by the 20th day the adults laid eggs that hatched and grew successfully into the nauplius stages. The detailed morphological characteristics of each developmental stage are presented and discussed in relation to A.clausi.