The development of marine calanoid copepods with comment on the isochronal rule1

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Abstract
Development times of seven species of planktonic marine copepods were determined at 15°C and excess food. Although details of instar durations varied among species, common trends were evident in relatively brief prefeeding stages and disproportionately long first‐feeding and C5 stages. Males tended to mature before females. There was no relationship between generation time and species size; ecologically dominant species developed from egg to adult in roughly the same time, 19–21 days. Isochronal development was most closely approached by species of Acartia but was not strictly followed by any of the animals studied. In population dynamics studies, the assumption of isochronality can result in substantial errors in estimates of instar‐specific mortality rates and, consequently, can seriously bias the interpretation of mortality patterns in nature and their possible causes.