Colurella obtusa Gosse, 1886
Most likely ID: n.a.
Synonym: n.a.
Sampling location: Simmelried, Purren pond, Ulmisried, Mainau pond, Pond of the convent Hegne, Bussenried, Bündtlisried
Phylogenetic tree: Colurella obtusa
Diagnosis:
- body obovoid
- lorica of two lateral plates, appear mussel-shaped
- length 70–90 µm (inclusive foot and toes)
- semi-circular hood covers corona
- anterior margin sloping ventrally
- posterior margin rounded or slightly pointed
- two lateral eyespots
- terminal foot segment short
- toes slender and sharply pointed (14–18 µm)
I find Colurella obtusa in almost all of my sampling sites, mostly among floating and decomposing plant material. The lorica of Colurella is similar in structure to a mussel shell. The two halves have an apical and ventral gap. This gap can close tightly when disturbed. Colurella also has a semi-circular hood that protects the corona (s. fig. 1 b).
The different species within the genus Colurella can essentially be distinguished by the shape of the lorica. In Colurella obtusa, the posterior end is either rounded or very slightly pointed (s. fig. 1 a). However, there is no spine at the posterior end, as in Colurella uncinata. The anterior margin of the lorica slopes downwards towards the ventral side (s. fig. 2). At the transition to the dorsal side, the lorica also forms a slight apical point (s. fig. 2).
More images and information on Colurella obtusa: Michael Plewka-Freshwater life-Colurella obtusa
Fig. 1 a-c: Colurella obtusa. L = 90 µm (total length). Different focal plans of a freely swimming specimen from right. Note the semi-circular hood (HO) covering the corona and the slightly pointed posterior margin of the lorica (arrow). FO = foot, Int = intestine, ST = stomach, TO = toes, Vit = vitellarium. Obj. 100 X.
Fig. 2: Colurella obtusa. The restracted specimen as shown in fig. 1 a-c. The anterior margin is sloping to the ventral side. Note the slightly pointed border between the ventral and dorsal margin of the lorica (arrow). Obj. 100 X.