Figure 1. A Stentor assemblage showing the main shape and macronucleus types (from Curds et al. (1983), modified). (a) Large (1–4 mm), slenderly trumpet-shaped species with a vermiform and a moniliform macronucleus, respectively. (b) Freely motile, turbinate specimen with coloured pigment stripes. (c) Small to medium-sized (100–1000 m), broadly trumpet-shaped species with single, spherical macronucleus. (d) Campanulate species.

Figure 2. An almost fully extended Stentor niger adhering to the microscope slide (courtesy of M. Kreutz, Germany). This beautiful species is up to 1 mm long, has a single globular macronucleus (MA), and is yellow-brown due to brownish pigment granules. Note the mighty adoral zone of membranelles (AZM), which swirls food particles into the huge buccal cavity (BC). AZM, adoral zone of membranelles; BC, buccal cavity; CR, ciliary rows; CV, contractile vacuole; FV, food vacuole; L, lorica; MA, macronucleus; PB, peristomial bottom; PS, pigment stripes; SC, sensory cilia.

Figure 3. Stentor multiformis (a, d) and S. amethystinus (b, c), both slightly squashed to show details of the organization (courtesy of M. Kreutz and P. Mayer, Germany). S. multiformis is a small species (length about 250 m when fully extended) with beautiful blue pigment stripes and a single globular macronucleus. The individual pigment granules are blue and about 1 m across. The narrow white zones between the pigment stripes contain the ciliary rows. S. amethystinus is a medium-sized species (up to 500 m long when fully extended), which appears dark at low magnification due to the lilac pigment stripes and the symbiotic green algae. This species often blooms in the pelagial of small lakes and ponds. AZM, adoral zone of membranelles; FV, food vacuoles; MA, macronucleus; PS, pigment stripes; SA, symbiotic green algae.