Water fleas

Code OG049999

DAPHNIIDAE: A family of the Cladocera (water fleas). Cladocerans of varied appearance.

A typical daphniid has a concave 'face' with the lower part produced as a rostrum, and a distinct spine (long, or short) at the posteroventral corner of the carapace.

However, some genera lack the rostrum or lack the spine, and must be distinguished from other similarly shaped cladocerans by other characters. Bosminidae with a spine can be distinguished readily by the long, downward-curved rostrum and having the antennules fused immovably to the head. Chydoridae (no spine) can be distinguished by their small and partly hidden antennae.

Macrothricidae, Moinidae, Ilyocriptidae and most Sididae are readily distinguished by lack of spine and lack of rostrum. However, some Sididae lack a spine but do possess a rostrum, a combination which occurs also in Daphniidae.

Externally the Sididae-like Daphniidae can be distinguished from Daphniidae-like Sididae because in these Daphniidae the rostrum is short. Internally, the body (trunk) in Daphniidae carries 4-5 pairs of appendages at least two of which are leg-like, while Sididae have 6 pairs of trunk appendages, all but the last being gill-like (foliose).

Daphniids are common inhabitants of the plankton and littoral zones of standing waters of all kinds. They function as grazers of bacteria and zooplankton, and provide a major food resource for young fish. Shiel (1995) provides a key to the five Australian genera plus notes and species-level keys to several taxa.

References:

Korovchinsky, N.M. (1992) The Sidiidae and Holopediidae (Crustacea: Daphniiformes). Guides to the Identification of the Microinvertebrates of the Continental Waters of the World. 3: 1-82. SPB Academic Publishers, The Hague.

Shiel, R.J. (1995) A Guide to Identification of Rotifers, Cladocerans and Copepods from Australian Inland Waters. Co-operative Research Centre for Freshwater Ecology Identification Guide No. 3., Albury, NSW.

Smirnov, N.N. and Timms, B.V. (1983) Revision of the Australian Cladocera (Crustacea). Records of the Australian Museum Supplement 1: 1-132.