Rotifers: Rotifera

Abstract

Rotifers (wheel animals) are widespread throughout the world (Fig. 6.1). They comprise a remarkably diverse group concerning their form, shape and species number, as well. More than 1000 species are known from Europe (Anon 2014; Barnes 1980; Damborenea et al. 2019; De Smet 1996; De Smet and Pourriot 1997; Donner 1956, 1965; Edmondson 1959; Fitter and Manuel 1986; Illies 1978; Koste 1978; Kriska and Tittizer 2009; Nogrady et al. 1995; Nogrady and Segers 2002; Pennak 1989; Pontin 1978; Quigley 1977; Ruttner-Kolisko 1974; Schwab 1999; Segers 1995; Thorp and Rogers 2015; Wallace and Ricci 2002; Wallace and Smith 2009; Wallace et al. 2006, 2015). Only some genera are present in the sea; the majority occurs in freshwaters. These latter species are abundant animals of all kinds of wet or moist habitats, including such incredible places like mosses and lichens, growing in roofs or even gutters. Should the habitat completely dry out, they contract, encapsulate and begin a dormant life (anhydrobiosis). In this state of suspended animation, rotifers may remain alive for several months or even years. When rehydrated, they quickly resume their activity within a few hours. They are well adapted to extreme environmental conditions; some species inhabit thermal springs, others live in the meltwater pooled on the surface of glaciers. Several rotifers are free swimming and are permanent or temporary members of the plankton (Fig. 6.2a, b). Some surface inhabiting species shin around on water plants, stones or on the muddy bottom (bdelloids—Bdelloidea, Fig. 6.2c), while others live on the armour of crustaceans or insects (epizootic species). The body length of rotifers is between 25 μm and 2 mm, yet most of them are around 200–400 μm, a size similar to that of the ciliated protozoans.