Keratella tropica (Apstein 1907)
This species was separated from K. valga by Berzins (1955). The distinguishing character, i.e. the hindmost median plaque of the dorsal lorica (the "postero-median remnant" according to the terminology used by Ahlstrom 1943), is clearly discernible in most individuals, although in some specimens it was very small and hardy visible.
Lorica compressed dorsoventrally. The anterior dorsal margin with six spines, medians being the longest, stoutest and curved ventralward. Lateral usually little longer than intermediate. Lorica with two unequal posterior spines. Right spine being always longer than the left. The left posterior spine is being absent in some specimens. The dorsal surface of lorica consists of three median polygones and a small four sides structure and three pairs of marginals. It bears two posterior spines on the lorica with the left spine shorter than the exuberant right one. This species show morphological (cyclomorphic) variation.
Lorica length 150-240 µm; width 65-90 µm; left posterior spine 32 µm; right posterior spine 85 µm.
Ecology and Distribution
It is widely distributed in tropical waters and extends very often into subtropical areas as a summer form.
- Anuraea valga tropica Apstein 1907 (basionym)