Biometry of the Copepod Calanus Finmarchicus (Gunn.) in Stages V and VI

Abstract

One hundred each of stage VI male and female and stage V Calanus finmarchicus were picked at random, and, by means of a projection microscope, measurements made on a number of segments in both metasome and urosome.The stage VI female population was mixed containing 95% of a smallsized population and 5% of a larger size-group. The males constituted a single population.At this time of the season the stage VI male and female metasomes are the same length, but there are differences in the sizes of the individual segments, the most striking of which is that of the headThe stage V animals in many of the measurements could be quite clearly separated into two size-groups of about 50% each and it is suggested that these are potential male and female populations. This separation at 50/50 has been noticed in numerous other collections of stage V, but it shouldbe emphasized that the differences are population differences in regard to those measurements considered.Evidence is presented which shows that the state of the antennules after preservation in 5% neutral formalin is unlikely in stage V animals to be a reliable guide to their sex in the next stage.