body ovoid to elliptical, dorso-ventrally flattened, deformable
length 37–138 µm
numerous, disc-shaped chloroplasts, yellowish gree to bright green
sometimes a lipid droplet in posterior part
contractile vacuole apically
layer of spherical mucocysts below pellicle
elliptical nucleus below contractile vacuoles
one leading flagellum and one trailing flagellum of body length
eyespot absent
extrusomes absent
Vacuolaria virescens
I find Vacuolaria virescens very common, especially in spring. Then it can also sometimes come to mass developments.
The cells are usually ovoid in shape, as shown in fig. 1 a-c. However, an elongated swim shape can also be adopted (s. fig. 2 a-c and fig. 3 a-d). The highly refractile, spherical mucocysts (s. fig. 2 b) react very sensitively to the coverslip and burst quickly.
Vacuolaria virescens can be confused with Vacuolaria viridis and Goniostomum semen. However, Vacuolaria viridis is smaller (usually less than 40 µm) with a heart-shaped cell form while Goniostomum semen has clearly visible extrusomes.
Fig. 1 a-c:Vacuolaria virescens. L = 61 µm. A freely swimming specimen. Note the leading flagellum (LF) and the trailing flagellum (TF). CV = contractile vacuole, Nu = nucleus. Obj. 60 X.
Fig. 2 a-c:Vacuolaria virescens. L = 80 µm. An elongated, freely swimming specimen. Note the layer of spherical mucocysts (Mu) beneaths the pellicle. CV = contractile vacuole, LF = leading flagellum, Nu = nucleus, TF = trailing flagellum. Obj. 100 X.
Fig. 3 a-d:Vacuolaria virescens. L = 63 µm. A third, freely swimming specimen. Note the numerous, disc-shaped chloroplasts (Chl). Obj. 100 X.
Fig. 4 a-b:Vacuolaria virescens. Two focal planes of a squashed specimen. Note the highly refractive mucocysts (Mu) beneath the pellicle. The disc-shaped (Chl) have a diameter of 3.5–4.0 µm. CV = contractile vacuole, Nu = nucleus. Obj. 100 X.