Menoidium gibbum (Skuja, 1939)
Most likely ID: n.a.
Synonym: Rhabdomonas gibba, Rhabdomonas spiralis
Sampling location: Simmelried
Phylogenetic tree: Menoidium gibbum
Diagnosis:
- cells curved, laterally compressed, slightly spirally twisted
- ventral with concave indentation
- posterior end tapered and bent to the right
- length 14–16 µm
- flagellum almost body length
- nucleus in mid-body with central nucleolus
- paramylon granules rod-shaped, arranged at the dorsal side
- pellicle densely longitudinally striated
- fast swimming, helically rotating
I have found only one specimen of Menoidium gibbum in Janur 2008 in Simmelried. After that I have not registered any more finds.
Menoidium gibbum has a very characteristic shape because of its posterior end is bent to the right (s. fig. 1 a), which practically excludes a confusion with other species. In addition, the ventral side is concavely indented (s. fig. 1 c). My specimen was 20 µm long and thus slightly longer than indicated by Skuja. Skuja found Menoidium gibbum mostly in spring after snowmelt. My finding in January could be an indication that Menoidium gibbum is a psychrophilous species.
Fig. 1 a-e: Menoidium gibbum. L = 20 µm. A freely swimming specimen from ventral (a, c, d), from left (b) and from right (e). Note the bent posterior end (BPE) and the ventral concave indentation (VC). F = flagellum, PG = paramylon grains. Obj. 100 X.