(Ehrenberg) Stein, 1878
Most likely ID: n.a.
Synonym: Astasia acus, Pseudoperanema acus
Phylogenetic tree: Heteronema acus
- cell spindle-shaped, tapered towards both ends
- length 40–56 µm, width 8–20 µm
- leading flagellum about body length
- trailing flagellum half of body length
- periplast with delicate striation running conterclockwise, sometimes smooth
- one contractile vacuole in anterior end
- nucleus central
- sometimes green and yellow remains of ingested algae
Heteronema acus is the most common representative of the genus Heteronema in my sampling sites. The species is well recognized by the spindle-shaped body and the trailing flagellum, which is about half as long as the body. The leading flagellum is usually slightly longer than the body and forms a lasso-shaped loop at the distal end, while the rest of the flagellum remains straight when swimming. Heteronema acus likes to settle on the floating coverslip and is then easy to observe.
Fig. 1 a-c: Heteronema acus. L = 59 µm. Three focal planes of a freely swimming specimen. Note the trailing flagellum (TF) directed to the posterior end parallel to the body. LF = leading flagellum. Obj. 100 X.
Fig. 2 a-d: Heteronema acus. L = 78 µm. A second, slightly squashed specimen. CV = contractile vacuole, IA = ingested algae, LF = leading flagellum, Nu = nucleus, TF = trailing flagellum. Obj. 100 X.
Fig. 3: Heteronema acus. L = 68 µm. Focal plane on the delicate striation of the pellicle (SP) of a third specimen. The striation is running counterclockwise to the posterior end. Obj. 100 X.