Hallberg, E. & H.J. Hirche. (1980). Differentiation of mid-gut in adults and over-wintering copepodids of Calanus finmarchicus (Gunnerus) and C. helgolandicus.
Journal of Experimental Marine Biology and Ecology. 48(3):283-295, figs. 1-9, tab. 1. (23-xii-1980).