Chydorus sphaericus occurs in more than 2/3 of the water bodies, and only Bosmina longispina is recorded from more localities. It is found everywhere and is very tolerant towards extreme environmental conditions.

Key characteristics

The morphology and size of Chydorus sphaericus varies a lot. However, populations of small individuals are most common. There is also a large amount of minor morphological variations between populations. To distinguish C. sphaericus from the close relative C. ovalis it has a less rounded outline of the posterior ventral corner. Postabdomen has 7–10 relatively small denticles with little variance in size. The colour varies with different variants of brown, but also with elements of green.

Female: Length 0.3–0.5

Male: Length 0.2–0.4

Ecology and distribution

C. sphaericus occurs in 2/3 (67 %) of the water bodies, and only B. longispina and A. elongata are recorded from more localities. It is found in all parts of Norway from sea level and up to 1544 m a.s.l. The frequency of water bodies that contains C. sphaericus is not varying with altitude. It is common in localities of all sizes and lives in a great variety of habitats. C. sphaericus is a very tolerant species and is recorded from lakes varying in pH between 3.7 and 9.9 and conductivity between 0.4 and 957 mS/m (brackish water).