Rotifera

Abstract

Rotifera is a moderately sized phylum of minute, bilaterally symmetrical, unsegmented animals that live predominantly in freshwaters. The phylum name (Latin, rota , wheel; ferre , to bear), first used by Cuvier in 1798, refers to the anterior end that in many species resembles a rotating wheel due to the sequential beat of its cilia. Rotifers have been found on every continent, occupying a diverse array of habitats, including marine, brackish and freshwaters, as well as the film of water that coats terrestrial mosses and particles in damp soils. In lakes rotifers often achieve high population densities (>1000 individuals per litre); thus, as consumers of bacteria, algae and protists they are ecologically important in transferring energy to higher trophic levels. As rotifers are a good food for young fishes, they are grown in mass quantities in commercial aquaculture. They also serve as models for research on ageing, and as bioindicators for ecotoxicology. Key Concepts: Rotifers have been found in the inland waters (both fresh and saline) of every continent, in the moisture covering some plants such as mosses, and in damp soil. Although generally not as abundant as in continental waters, rotifers often flourish in nearshore marine waters and estuaries. Many rotifers are capable of undergoing dormancy, either as adults or embryos, allowing them to disperse in space or time and often avoid harsh conditions. Feeding mainly on other microscopic organisms, including bacteria, algae and protists, rotifers are important basal consumers in aquatic systems. In certain lakes, rotifers play an important role connecting the microbial loop to the classic food web, whereby the dissolved organic carbon is taken up by the bacteria that are consumed by rotifers, which in turn are consumed by higher trophic levels. In this way, a portion of the energy in dissolved organic matter is returned to the food web. As they are the first food for larval organisms, rotifers have been exploited by aquaculturists to maintain commercially important fishes, shrimps and crabs. As they are comparatively inexpensive and easy to culture and possess relatively short life spans, rotifers are used in ageing studies and to assess the toxicity of compounds such as heavy metals, pesticides and pharmaceuticals. Some species of rotifers have specific ecological requirements making them useful as indicators of water quality. The phylogenetic position of rotifers has not yet been resolved, but they appear to be related to a group of small, jawed metazoans (Gnathifera). Acanthocephala, an entirely parasitic phylum, are now considered to be highly aberrant rotifers. Over the years rotifers have entered the collective culture ethos as subjects of poetry, science fiction and children's literature, artists' workings in glass and mixed media and pop music.

Direct and indirect effects of invertebrate predators on population level responses of the rotifer Brachionus havanaensis (Rotifera)

“…E. najas is frequently found in the littoral of freshwater bodies . In the shallow lakes of Mexico it co‐exists with B. havanaensis .…”

“…Induced defenses are commonly observed in prey subject to varying levels of predation risk, and if the defense structure incurs a maintenance cost . These criteria are met by most rotifers, which detect their predators, prey or conspecifics by chemical stimuli and where the defenses in the form of long spines also affect the floating/sinking rates .…”

Rotifers of temporary waters

“…Sample preservation techniques depend on the ultimate fate of the material. As noted in Wallace and Snell , for taxonomic identification some species must be examined live, while others are best identified when preserved in buffered formalin solution. Lugol's iodine and Rose Bengal stain can be used to enhance visibility for counting purposes.…”

“…The two main subclasses of rotifers, bdelloids, and monogononts, use different strategies to survive in a dormant ametabolic state. Bdelloids undergo quiescence, marked by a change in metabolism progressing into the anhydrobiotic state of the xerosome . Adult bdelloids as well as their eggs can survive repeated cycles of freezing and thawing .…”

Ultrastructural and elemental characterization of the extracorporeal tube of the sessile rotifer Floscularia conifera (Rotifera: Gnesiotrocha)

“…Phylum Rotifera comprises ~2,000 species of mostly freshwater microinvertebrates, of which the planktonic species are particularly well‐studied (Segers, ), but the majority of which are benthic periphytic forms. In freshwater systems, rotifers are present from the littoral to the limnetic zones and form an important part of the microbial loop (Wallace, ). Rotifers are characterized in part by a ciliated region (corona) on top of the head, which functions for both locomotion and food gathering (Wallace, ).…”