Paper Received: 28.11.2019 Revised Received: 11.12.2019 Accepted: 12.12.2019

Journal Home page : www.jeb.co.in « E-mail : [email protected] Review Article Journal of Environmental Biology TM p-ISSN: 0254-8704 e-ISSN: 2394-0379 JEB CODEN: JEBIDP DOI : http://doi.org/10.22438/jeb/41/1/MRN-1344 White Smoke Plagiarism Detector Just write. Review on the ecology and taxonomy of sessile rotifers (Rotifera) with special reference to Mexico S.S.S. Sarma1*, M.A. Jiménez-Santos2, S. Nandini1 and R.L. Wallace3 1Laboratory of Aquatic Zoology, National Autonomous University of Mexico, CP-54090 Tlalnepantla, México 2Posgrado en Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, CP-04510, Mexico 3Department of Biology, Ripon College, Ripon, WI 54971-0248, USA *Corresponding Author Email : [email protected] Paper received: 28.11.2019 Revised received: 11.12.2019 Accepted: 12.12.2019 Abstract Although comprising <0.5% of all the known species of Rotifera, sessile rotifers are an important component in freshwater ecosystems, especially shallow waterbodies. During the last eight decades, fewer than 80 publications have dealt specifically with sessile rotifers, while more than 7600 articles have focused on rotifers in general. In this work research on the sessile rotifers with emphasis on the Mexican fauna has been reviewed and some additional information on the new records has been included. Difficulties involved in collection and maintenance of sessile rotifers, as well as problems of identification and quantification have been considered. Published data on the ecology and taxonomy of this group has also been reviewed. There are 35 species of sessile rotifers from three families Atrochidae, Collothecidae, and Flosculariidae, but to that four more species in the planktonic family Conochilidae may be added, as recent molecular research indicates that this family lies within Flosculariidae. The inventory includes new records for Mexico and one poorly described species. The number of sessile rotifer species known from Mexico is still low considering the large number of shallow water bodies present in Mexico. Comments regarding the importance of substratum (macrophyte) type and the significance of physical structure in providing substratum for larval stages of sessile rotifersOnline have been Copy made. Key words: Distribution, Freshwater ecosystem, Macrophytes, Mexico, Sessile rotifers How to cite : Sarma, S.S.S., M.A. Jiménez-Santos, S. Nandini and R.L. Wallace: Review on the ecology and taxonomy of sessile rotifers (Rotifera) with special reference to Mexico. J. Environ. Biol., 41, 3-12 (2020). © Triveni Enterprises, Lucknow (India) Journal of Environmental Biology January 2020 Vol. 41 3-12 4 S.S.S. Sarma et al.: Ecology and taxonomy of sessile rotifers Introduction feeding on algae, diatoms, and detritus they transfer energy to higher trophic levels, which otherwise can be expected to pass Phylum Rotifera is a group of micrometazoans of about through the detrital cycle or microbial loop (Wallace et al., 2015). 2000 species with exceptional characteristics that make them Indeed popular literature depicts many sessile rotifers as nature’s model organisms in basic and applied research, including aging, water purifiers (Walsh, 1979). In spite of this, literature on rotifers is ecology, evolution, systematics, biodiversity, aquaculture, and strongly biased towards planktonic taxa. For example, information ecotoxicology (Wallace et al., 2015; Declerck and Papakostas, retrieved from the Web of Science, reveals that though the global 2017). Some of these characteristics are their small size within study of rotifers is on the rise, that of sessile rotifers is lagging (Fig. Metazoa (40–3000 µm), presence of a muscular pharynx 1). During the last eight decades, approximately 70 publications (mastax) with jaws (trophi), and three modes of reproduction deal specially with this group. The study of sessile rotifers has been (Wallace et al., 2015). Reproduction is exclusively sexual in emphasized by researchers in just four countries; USA, Belgium, species of small marine family Seisonidae. On the other hand, in India, and Thailand (37, 10, 8, and 5 publications respectively). the four families of Bdelloidea reproduction is exclusively Mexico, like the rest of the world, has not only limited information on asexual. With 30 families, Monogononta comprises the bulk of this group but also scattered in different journals. Rotifera. In this group most reproduction is parthenogenetic, but in many (but not all) species, this asexual pattern is broken by Aquatic plants offer substratum for a wide variety of both, brief periods of sex with the production of haploid eggs. If one of peripheral and epiphytic organisms. The structural complexity of these eggs remains unfertilized a male develops, but if it is macrophytes also serves as a refuge against predation (Walsh, fertilized, a diapausing, resting stage (resting egg) develops. 1995) and are a rich source of food resources due to their high These cyst-like structures have a mean volume of ~6.8 x 105 µm3, epiphytic phytoplankton diversity (Jeppesen et al., 1998). Mexico but their known volumes many range from 0.1 to 97.4 x 105 µm3 has a great diversity of macrophytes (hydrophytes) (Lobato-de (Walsh et al., 2017). Once released from the parent, a resting egg Magalhães and Martínez, 2018), which can potentially house (RE) sinks to the bottom of the habitat where it remains until many sessile rotifers but have been ignored in rotifer diversity conditions are suitable for hatching. studies (Walsh et al., 2008). Here studies on diversity of sessile rotifers in Mexico with emphasis on some salient taxonomic Survivorship reduces with aging, but some REs may features, sampling strategies, identification, and quantification remain viable for decades (Wallace et al., 2006). In ephemeral have been reviewed and with some data on the new records. habitats that dry, winds can loft REs along with dust and sand and Because study of sessile rotifers involves live individuals, some disburse them many kilometers downwind (Rivas, Jr. et al., 2018, aspects of their culture techniques have been included here. 2019). Extraordinary resistance to harsh conditions is also seen in bdelloids. They occur in extreme conditions (e.g., frozen Collection and Maintenance waters, thermal springs, hypersaline waters, etc.) (Wallace et al., 2006). Bdelloids also have been shown to withstand ionizing For most species, study of sessile rotifers require living radiations of >1000 Gy, (e.g., Philodina roseola: Gladyshev and individuals and depending on the type of macrophyte being Meselson, 2008). Collectively rotifers occupy a range of habitats. examined, the entire submerged plant, should be collected. For They may be free living in the plankton and/or benthos, epiphytic, floating macrophytes, of course, this means that the roots are epizoic, ectoparasitic (e.g., fish gills), or endoparasitic (e.g., in sampled and observed. In some cases, macrophytes from the colonial algae such as Vaucheria and Volvox or animals such as field can be kept in a bucket of pond water with mild aeration to aquatic oligochaetes and snail eggs) (May, 1989; Rao, 1993; maintain suitable oxygen concentrations. This technique may Wallace et al., 2001). Their feeding strategies coupled with short release attached species from the plant into the water column, lifespan (<4 weeks) and short generation time (days to 2 weeks), which can be then filtered out (H. Segers, personal communication). rapid growth rates, and numerical abundance results in their However, this is partially successful because many species are central trophic position in freshwater ecosystems and their vital permanently attached to macrophytes. Note that any forceful importance in aquaculture (Sarma and Nandini, 2017). attempt at detaching specimens can result in their damage. Studies on the ecology and taxonomy of rotifers focus on Rotifers associated with macrophytes collected from the planktonic species usually based on formalin-fixed samples. field can be maintained in aquaria without providing additional However, many species possess a soft bodyOnline wall (illoricate); food such asCopy algae because they depend on periphytic algae and these species lose their shape upon fixing and, thus, become detrital matter and associated organisms such as bacteria. nearly unidentifiable (Wallace et al., 2006; 2015). Besides their Depending on the volume of the aquarium and the amount of soft lorica, study of sessile rotifers is further complicated by the plant material no aeration may be needed. However, care should habitat in which they are found, mainly macrophytes, which are be taken to prevent anoxic conditions from developing; in that frequently ignored in routine limnological investigations (Walsh et case the plant material will decompose and cause complete al., 2008). Though there are about 100 sessile rotifer species, i.e., deterioration of the system and a decline in rotifer species <0.5% of all rotifers, they play an important role as planktonic taxa richness and density. Sessile rotifers collected from the eutrophic in energy transfer, perhaps more so in shallow waterbodies. By waterbody, Lake Xochimilco survive for longer than a month by ¨ Journal of Environmental Biology, January 2020¨ S.S.S. Sarma et al.: Ecology and taxonomy of sessile rotifers 5 replacing 50% of lake water with synthetic medium such as EPA the specimen, care should be taken so that the animal is not (Sarma et al., 2017). However, frequent replacement (e.g., weekly) crushed (Wallace et al., 2006).

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