Cephalodella gracilis (Ehrenberg, 1830)
Most likely ID: n.a.
Synonyms: Cephalodella gracilis var. lenticulata, Cephalodella gracilis var. sigmoides, Cephalodella sagitta
Sampling location: Mainau pond, Purren pond
Phylogenetic tree: Cephalodella gracilis
Diagnosis:
- body rather short, laterally compressed, slightly gibbous dorsally
- length 135–152 µm
- head relatively short and convex anteriorly
- neck is well marked
- lorica is thin and flexible, lateral clefts narrow
- corona is oblique and strongly convex without projecting lips
- toes short, slender, slightly recurved and gradually tapering
- eyespot frontal
- retrocerebral organ absent
- vitellarium with four nuclei, rarely with six nuclei
I have found Cephalodella gracilis so far only in the Mainau pond and in the Purren pond in the upper mud layer. The species is mostly smaller than 150 µm and is immediately noticed by its small size. Important features for classification are the apical eyespot, the dagger-shaped toes and the vitellarium with only 4 nuclei (s. figs. 2a and 3). The latter is a very characteristic feature, since most Cephalodella species have 8 or 12 nuclei in the vitellarium.
Fig. 1 a-c: Cephalodella gracilis. L = 110 µm. A freely swimming specimen from left. Obj. 100 X.
Fig. 2 a-c: Cephalodella gracilis. L = 138 µm. A slightly squashed specimen from right. Note the 4 nuclei of the vitellarium (NV). Obj. 100 X.
Fig. 3: Cephalodella gracilis. A strongly squashed specimen from right. The 4 nuclei of the vitellarium are visible (1-4). ES = apical eyespot, DA = dorsal antenna, TR = trophi. Obj. 100 X.
Fig. 4: Cephalodella gracilis. The trophi in a strongly squashed specimen. Obj. 100 X.