Rotifers and Meiofauna

The Rotifers

Three classes

Rotifers are microscopic metazoans, characterized by a body-size ranging from 40 μm to 2 mm. Worldwide, rotifers are represented by more than 2000 described species. Many more species are yet undescribed.
Their most conspicuous features are the ciliated corona used for locomotion and food collection, and the mastax, a muscular pharynx that possesses hard jaws or a trophi. Rotifers can be sessile, but most species are free moving, either swimming or crawling. Few sessile species are parasitic. No other metazoan group is represented by so many different body forms and shapes.
Generally, three groups of rotifers are recognized: the Monogononta, the Bdelloidea and the Seisonacea. Each group has its specific morphology, reproduction mode and ecology.
Rotifers occur in a wide variety of habitats, aquatic and semiaquatic, including soils, mosses, and even more extreme biotops such as soda-water bodies, acidic ponds, streams and peat bogs. Some rotifers have a strict parthenogenetic reproduction, some are viviparous, some lay resting eggs. Rotifers are capable to survive very harsh environmental condictions, including long periods of desiccation, through anabiosis.

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The Meiofauna

Variety of Taxa

Meiofauna are benthic organisms defined within a body size-range located between the macro- and the microfauna (i.e. flagellates, ciliates).
Thus, freshwater meiofauna includes all taxa and individuals of animals that pass through a 500 μm sieve and are retained by a 42 μm sieve.
The meiofauna is composed of taxa that vary widely in form and shape, and includes animals from different phyla. Two forms of meiofaunal groups can be differentiated: the ‘permanent’ meiofauna which are taxa that remain their whole life history within the meiofaunal size range, and the ‘temporary’ meiofauna which includes all smaller larval or nymphal stages of freshwater macroinvertebrates.
Meiofaunal species are found in both marine and freshwater systems at sediment surfaces and in the interstitial of subsurface sediments as well as on aquatic plant surfaces. In freshwater systems, the permanent meiofauna is comprised of: Testacea, Gastrotricha, Microturbellaria, Rotifera, Nematoda, Oligochaeta, Tardigrada, Hydrachnidia and microcrustaceans (Cladocera, Copepoda, Ostracoda). Temporary meiofauna are aquatic insects such as larval Chironomidae, small nymphs of Plecoptera and Ephemeroptera.

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