a. The heterocysts react specifically with FITC-ConA, while photosynthetically active cells are ConA-negative. Besides the heterocysts, the loricas of two choanoflagellates are labeled. Choanoflagellates live on the outside of Anabaena cells. b. Acinetes are resistant stages. They can be stained with FITC-RCA and appear in the case of Anabaena flos-aqua during the terminal stages of an algal bloom. They occur in pairs to the right and to the left of a heterocyst (U. MÜLLER and P. v. SENGBUSCH, 1983).