Pandorina morum
(Müller) Bory, 1824
Most likely ID: n.a.
Synonym: n.a.
Sampling location: Mühlweiher Litzelstetten, Simmelried, Pond of the waste disposal company Constance, Mühlhalden pond, Pond of the convent Hegne, Purren pond
Phylogenetic tree: Pandorina morum
Diagnosis:
- colonies are ovoid or ellipsoidal of 8–16 cells
- colonies covered by a gelatinous sheath
- colonies 20–50 µm in diameter
- cells wedge-shaped, compactly arranged radially
- diameter of cells 8–17 µm
- each cell with two flagella of equal length
- 2 contractile vacuole at base of flagella
- eyespots present
- chloroplast cup-shaped, longitudinally striated
- one pyrenoid per cell (rarely more)
I find Pandorina morum very frequently, both in the plankton and among floating or decomposing aquatic plants. This volvococcal alga is particularly common in spring.
The colonies of Pandorina morum appear very compact because the cells are arranged without a gap in the gelatinous matrix. Their shape is therefore wedge-shaped and not round (s. fig. 2 b). Two flagella of equal length arise at the apical end and pierce the gelatinous envelope through two short canal (s. fig. 1 b). At their base are two contractile vacuoles and an orange-red eyespot (s. figs. 1 a and 2 a). The chloroplast shows a characteristic striation (s. fig. 2 a).
Pandorina morum is often confused with the equally common volvococcal alga Eudorina elegans. However, the colonies of Eudorina elegans are considerably larger (50-200 µm) and the round cells are clearly separated from each other.
Fig. 1 a-b: Pandorina morum. D = 57 µm (of colony). Two focal planes of a freely swimming colony of 16 cells. Note the two flagella (F 1, F 2) of equal length and the sharply defined gelatinous sheath (GS) covering the colony. ES = eyespot. Obj. 100 X.
Fig. 2 a-b: Pandorina morum. D = 51 µm (of colony). A second colony of 8 cells. Note the densely arranged, wedge-shaped cells and the contractile vacuoles (CV) located near the surface of the colony. Nu = nucleus. Obj. 60 X.