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Studies of rotifer community composition and dynamics often rely on limited sampling regimes. To determine how well species richness is reflected in these studies, we examined interannual variation of rotifer species richness and monogonont community structure from 10 aquatic systems comprising four habitat types—springs, rock pools (tinajas), former cattle tanks, and artificial ponds—in Big Bend National Park (Texas, USA). Planktonic, littoral, and benthic samples were collected from all sites at about the same date for each of five summers (2001–2005). Our survey yielded 15 monogonont families including 30 genera and 84 species. Two bdelloid taxa also were designated. Species richness varied widely among these four habitats: range, 1–32; mean (±1 SD), 11.2 ± 8.0. Total Species richness in the habitats also varied considerably: springs (54 taxa) > artificial ponds (35 taxa) > tinajas (19 taxa) > cattle tanks (15 taxa). Sessile species comprised ≈13% of the taxa in our samples. Species turnover indices (STI) of these systems indicate low overall relatedness: mean (±1 S.D.) = 85.2 ± 7.1%. The relative frequency of encounter of most taxa in the four systems was low, with 79 taxa (≈92%) having values ≤2.0%. Singleton rates were quite high, ranging from 46.7 to 71.4%, with an overall mean ≈65.1%. Most importantly, we found that both species richness and STI varied considerably among habitat type. Species richness varied by 2–10× between consecutive years and STI ranged from 64 to 89% over the entire study. Our results indicate that rotifer community composition fluctuates greatly over time, and that rotifer community structure may be more labile than is generally believed. Species richness and thus biodiversity may be dramatically underestimated using single sampling or short-term strategies that are often employed in studies of zooplankton community structure.

Encompassing >2000 species, rotifers are microscopic zooplankton with short (∼1 to a few weeks) lifespans. In the ecosystem, they transfer energy from their prey (e.g., bacteria, algae, protists, and other rotifers) to their predators (e.g., larval fish), thereby linking the microbial loop with the classic food web. Cryptic speciation and diversity of life history strategies, including asexual, sexual, and cyclically parthenogenetic reproduction, recommends their use for studying basic ecological themes such as the basis for discriminating species, and the interplay of dispersal and biogeography. Rotifers inhabit a range of systems unified by the presence of water, but even in temporarily dried or frozen regimes rotifers can persist as dormant stages. Molecular tools and sequencing are resolving decades-old debates of the phylogenetic position of Rotifera and even of species within the phylum, complementing classic approaches of morphological-based species identification. From a practical standpoint, rotifers are important in aquaculture and ecotoxicological studies.

Colonies of the freshwater colonial rotifer Sinantherina socialis (Monogononta, Flosculariidae) have been shown to be unpalatable to a variety of small-mouthed, zooplanktivorous fishes. To test whether invertebrate predators ingest the rotifer S. socialis, we conducted two types of experiments: (1) Microcosm experiments—in separate experiments, four invertebrate predators (i.e., dragonfly nymphs, damselfly nymphs, notonectids, and Hydra) were offered prey either singly or in combination. Prey were comprised of S. socialis; Epiphanes senta, a solitary, free-swimming rotifer; and Daphnia magna, a microcrustacean. In each experiment, the percent of prey surviving after 12, 18, and 24 h was recorded. (2) Paired-feeding experiments—in separate experiments, predators were offered prey in a pairwise fashion, in which members of D. magna were alternated with a rotifer, either S. socialis or E. senta. The results of the microcosm experiments showed that, after 24 h, 60–100% prey items of S. socialis survived the predators, but significantly fewer individuals of E. senta (6–89%) and D. magna (

We investigated the phylogenetic relationships of Family Asplanchnidae using both morphological and molecular data. The morphological database, comprising 23 characters from 19 taxa (15 Asplanchnidae and 4 outgroups), was compiled from a survey of the literature and our own observations; the molecular data (ITS and V4 region nuclear regions and mitochondrial cox1) was sequenced from specimens that we collected. Our analysis of the morphological data set (maximum parsimony) yielded 12 most-parsimonious trees with a tree length of 27 steps. From this analysis we conclude (1) Asplanchnidae is a monophyletic group as are the three genera comprising it, (2) there is no compelling support for the argument that Asplanchna should be separated into two discrete genera, and (3) there is some support for the proposal that Asplanchnidae and Synchaetidae are sister groups. Our analysis of the molecular data set supports the first two of these conclusions while the sister group of the family varied depending on the gene region analyzed and families and genera included. Current understanding of the phylogeny of Asplanchnidae is hampered by the need for additional informative morphological characters and a lack of molecular data for the genus Harringia and several other members of the Asplanchnidae.

Floscularia ringens is a cosmopolitan, sessile rotifer (class Monogononta) that lives inside a tube it constructs from numerous small, rounded pellets. Adults of F. ringens produce parthenogenetic eggs that are retained within the tube. Upon hatching, juveniles remain within the maternal tube for a short time completing their development before swimming away. The free-swimming juvenile has a conical body, short foot, small corona, and mastax with trophi, but appears unable to feed. After a short time (

To resolve several taxonomic problems within the family Conochilidae (Rotifera, Monogononta, Flosculariacea), we initiated a comparative study of the morphology in this and related taxa using samples collected from widely separated geographical regions. As part of this study, we paid special attention to trophal morphology using scanning electron microscopy. We also constructed and analysed a data matrix comprising 19 morphological characters of 11 taxa using cladistic methods to uncover all most-parsimonious trees. The results indicate that Conochilidae share a body form with Flosculariidae, but they possess a trophal structure which clearly differentiates them from all other Flosculariacea; thus, the diagnosis of the family Conochilidae is amended to incorporate morphological characters of the trophi. The analysis of our data matrix yielded a single, most-parsimonious tree. From the topology of that tree and our scanning electron microscopy observations, we propose the following: (1) the status of Conochilidae as a separate suborder of Flosculariacea is rejected; (2) taxonomic separation of Conochilus and Conochiloides as subgenera of Conochilus is confirmed; and (3) Lacinularia causeyae Vidrine, Mclaughlin & Willis, 1985 is reallocated to a new genus within the family Conochilide, Conochilopsis gen. nov., as Conochilopsis causeyae (Vidrine et al.) comb. nov.

The presence of galls on species of Vaucheria was investigated both seasonally and in a number of locations in North America. These galls are induced by the rotifer, Proales werneckii . In an Ohio stream, Vaucheria bursata and V. geminata were found to have galls throughout their growing season; September to January. Galls were most abundant in October and ranged in size from 90–260 μm in width and 140–790 μm in length. New records of Vaucheria with galls from locations in Alabama, California, Georgia, Louisiana, North Carolina, Ohio and Tennessee are reported. Three of the five taxa collected were not previously known to contain galls. In addition, worldwide literature on the distribution of these associated taxa was reviewed.

The genus Notholca has been subjected to taxonomic analysis, using cluster analysis and ordination by principal coordinates analysis, based on 67 phenetic characters. All analyses converge on essentially identical groupings, but fail to inject new hypotheses to remedy the confusing and overlapping taxonomy of the genus. This shortcoming is ascribed to the incompleteness of the character set which currently lacks biochemical and genetic parameters. We suggest to invalidate the subspecies' of N. striata into a single species and consider the pros and cons combining N. haueri and N. latistyla.

Following ICZN (1999) Article 79 Chapter 17 http://www.nhm.ac.uk/hosted-sites/iczn/code/), we, with the full support of the international community of rotifer researchers as expressed during subsequent international Rotifera symposia, developed a Candidate Part of the List of Available Names for species and genera of Rotifera from the start of zoological nomenclature to the year 2000.

Many, mostly older, names of animal species are nomenclaturally problematic, either because their orthography is unstable, or they cannot be linked reliably to a taxonomic identity, due to the lack of recognisable descriptions and/or types. Yet, they represent available (sensu International Code of Zoological Nomenclature) names and must be taken into account in zoological works. This situation, with available senior, yet dubious names confounding nomenclature, is undesirable. It creates uncertainties at a time when molecular approaches are revolutionizing our concepts of species diversity, and fails us when the current extinction crisis calls for efficient, accurate, and constructive approaches to document, monitor, and conserve biodiversity. The International Code of Zoological Nomenclature (The Code) provides a means to address this issue by restricting availability, application and orthography of names to those included in the List of Available Names in Zoology (LAN). The Code (Art. 79) allows an international body of zoologists in consultation with the Commission to propose a candidate part of the LAN for a major taxonomic field. We explore this possibility for 3570 species-group names of Phylum Rotifera (of which 665 are problematic), by presenting such a candidate Rotifera part of the LAN. The web site of the International Commission on Zoological Nomenclature (http://www.iczn.org) will hold both the candidate list and a forum to facilitate consultation on the candidate list, while the list itself also can already be freely downloaded from three other Internet sites: http://fada.biodiversity. be, http://rotifer.ansp.org/LAN, and www.hausdernatur.at/rotifera. We give here an overview of the general approach and procedures applied in preparation of the candidate list, and anticipate that our effort will promote the process as well as result in a standard list of names for use in taxonomy, the Global Names Architecture and other biodiversity information initiatives.

Many, mostly older, names of animal species are nomenclaturally problematic, either because their orthography is unstable, or they cannot be linked reliably to a taxonomic identity, due to lack of recognisable descriptions and/or types. Yet, they represent available (sensu International Code of Zoological Nomenclature; The Code) names and must be taken into account. This situation is undesirable: available senior, yet dubious names confounding nomenclature. It creates uncertainties at a time when molecular approaches are revolutionizing concepts of species diversity, and fails us when the current extinction crisis calls for efficient, accurate, and constructive approaches to document, monitor, and conserve biodiversity. The Code provides a means to address this issue by restricting availability, application, and orthography of names to those included in the List of Available Names in Zoology (LAN). As allowed by The Code (Art. 79), the international assembly of rotiferologists at the 12th Rotifera Symposium (Berlin, 2009) mandated us to propose to the Commission, a candidate part of the LAN for Phylum Rotifera. We explored this possibility for 3570 species-group names of Phylum Rotifera (of which 665 are problematic), by presenting such a candidate Rotifera part of the LAN; the list is now open for discussion on the web site of the International Commission on Zoological Nomenclature (http://www.iczn.org). This site holds both the candidate list and a forum to facilitate discussion. The list itself also can be freely downloaded from three other Internet sites: http://fada.biodiversity.be, http://rotifer.ansp.org/LAN, and www.hausdernatur.at/rotifera. Here we provide an overview of the general approach and procedures applied in preparation of the candidate list and update the present status of the candidate part of the LAN. We further illustrate how our effort can contribute to a standard list of names for use in taxonomy, the Global Names Architecture and other biodiversity information initiatives.

Here we describe an on-going study of the rotifers inhabiting a sampling of springs (seeps), streams, ponds, tanks (diked ephemeral streams), and huecos and tinajas (small and large rock pools) of Big Bend National Park, a 3.23 × 105 ha region of the northern Chihuahuan Desert located in southwestern Texas (USA). We collected samples from planktonic, littoral, and benthic habitats comprising 92 sites representing 23 different aquatic systems. We documented 19 rotifer families (17 monongonont; 2 bdelloid) comprising 32 genera and 94 taxa. Of these, 70 were identified to species; 24 taxa (14 monogononts and 10 bdelloids) remain unidentified; several may be new to science. Redundancy Analysis revealed significant associations between environmental parameters and species distributions among water sources. Highest species richness was found in more permanent habitats such as ponds and springs while species associated with rock pools were associated with high conductivity and temperature.

The unusual parasitic association between Proales werneckii (Ehrenberg, 1834) (Ploimida: Proalidae) and the psychrophilic, coenocytic, filamentous alga, Vaucheria De Candolle, 1801 (Xanthophyceae: Vaucheriales), is documented using light and electron microscopy. A young female rotifer colonizes a Vaucheria filament (ca. 80 µm × 10 cm) by gaining entrance to the cell at a growing region where the wall has not yet matured. After achieving access to the cell, it disrupts development of either a gametophore or an apical tip by inducing cell hypertrophy and formation of an excrescent gall (ca. 80–120 × 140–1500 µm). Remaining within the vacuole of the gall for the rest of her life, the female deposits her eggs after feeding on the rich food supply furnished by the alga’s organelles which continue to translocate within the cytoplasm. This abundant nourishment provides the adult rotifer with energy sufficient to permit an enormous reproductive potential (e.g. galls with >80 subitaneous eggs have been seen). Upon hatching, some offspring emigrate to other immature gametophores or growing tips within the same filament, while others may leave to colonize new filaments. Here, we present the life history of this parasitic relationship, highlighting previously unknown aspects of the association as well as noting differences among the accounts of previous authors. To our knowledge, this is the first description of this parasitic relationship to include electron photomicrographs.

Correlations of egg and body volumes of 65 species of oviparous Rotifera from the three families of sessile rotifers (Atrochidae, Collothecidae, Flosculariidae) were determined from size measurements documented in the literature and from unpublished data (RLW). While egg volume (EV) of amictic (subitaneous) eggs increased as a function of body volume (BV) in these families, relative egg volume (REV) decreased with increasing BV indicating that relative investment per offspring is less in larger-bodied species. Regression coefficients for REV as a function of BV for these families were significantly different from each other and that of the strictly planktonic species studied by Walz et al. (1995). Thus, our statistical analysis indicates that relative investment per offspring was greatest in planktonic species, intermediate in Flosculariidae, and lowest in Collothecidae. These results suggest that the sessile families do not follow the standard pattern of EV predicted for planktotrophic and lecithotrophic larvae as is found in many marine benthic invertebrates.

We investigated phylogenetic relationships of phylum Rotifera using cladistic analysis to uncover all most-parsimonious trees from a data set comprising 60 morphological characters of nine taxa: one Acanthocephala, six Rotifera, and two outgroups (Turbellaria, Gnathostomulida). Analysis of our matrix yielded a single most-parsimonious tree. From our analysis we conclude the following: (1) Class Digononta is paraphyletic; (2) it is still premature to reject rotiferan monophyly; (3) the classification hierarchy that best conforms to this morphologically based, cladistic analysis is similar to several traditional schemes. In spite of these results, it is significant that this analysis yielded a tree that is incongruent with those trees developed from molecular data or by using the principles of evolutionary taxonomy.

Rotifers have attracted the attention of biologists for well over 200 years. Interest in these exquisite animals rests in their diverse morphology, short generation time resulting in high growth rates, ability to withstand desiccation, and wide distribution, coupled with evidence of cryptic speciation. Moreover, three modes of reproduction are present in the phylum: obligatory sexuality, cyclical parthenogenesis, and obligatory ameiotic parthenogenesis. Thus, this phylum offers a rich field of study. Recognizing the need to share advances in knowledge, a triennial meeting, the International Rotifer Symposium (IRS), was begun in 1976. The most recent symposium (13(th) IRS) was held at Shillong (India) from 18-24, November 2012. In this commentary we considered the development of rotifer research as viewed through the lens of more than 35 years of IRS. Initially papers presented at the IRS focused on ecology, morphology, and pure taxonomic problems, with little applied work being reported. However, after more than three decades, the emphasis has swung to a balance of both basic (e.g., aging, ecology, genetics, and taxonomy) and applied (aquaculture and ecotoxicology) research.

By rotating on a short, flexible, pedal stalk, Cupelopagis vorax captures prey that traverse the substratum to which this sessile rotifer attaches. Microvideographic analysis (including slow motion and freeze-frame) permitted us to examine some of the details of Cupelopagis foraging behavior. When undisturbed, Cupelopagis usually faces forward in a resting or neutral position (NP) with its unciliated infundibulum (corona) directed parallel to the surface of the substratum. However, vibrations produced by artificial means (fine pins) or small prey (protists) evoke unique behaviors in Cupelopagis. Our analysis of Cupelopagis foraging on two protozoan prey (Paramecium bursaria and a small, unidentified flagellate, SUF) indicates that this predator possesses a 360 ° encounter field (EF) biased towards the NP Size of the EF appears to be a function of both predator and prey size, but it extends at least 650 µm, as measured from the point of attachment of the predator's pedal stalk to the substratum. When a prey comes close to Cupelopagis, this predator can lean toward the organism, stretching forward on its pedal stalk and extending its corona over the prey in a swift motion (< 0.5 s). Probability of capture after attack was a function of prey type (61.6% for P. bursaria and 41.5% for the SUF). Analysis of prey capture by Cupelopagis indicates that this predator has a handling time ranging from a few seconds to several minutes: 24.6 ± 16.8 s for P. bursaria (n= 274) and 34.6 ± 25.4 s for the SUF (n=111). Occasionally Cupelopagis sweeps part of the EF by retracting its corona, turning to the right or left (mean angle subtended ≈ 63 ° ± 42 °), unfolding the corona, and slowly returning to the original resting position. This behavior, termed surveillance, occurs in the presence or absence of prey. While not unique in its ability to detect water movements, Cupelopagis is the only rotifer known to exhibit specific behaviors to vibrations produced by potential prey.

The Harbor Science and Arts Charter School is a small, public elementary school with children in grades 1 through 7 located in the East Harlem section of New York City. A hallmark of our curriculum is that we encourage students to work on group projects and to make many oral presentations of the results of their work. We noticed that when children were engaged in group work and oral presentations, it was often difficult to understand everything that was said. One of our fourth grade teachers had a friend who was an acoustical designer who arranged a sound analysis of the teacher’s room that confirmed that our high ceilings, concrete block walls, and window air conditioners were creating some of the problems we were experiencing. Using the room as a test case, Armstrong Industries donated materials for modifications to the room. They subsidized lowering the ceiling with acoustical tiles. We installed new bulletin boards and purchased new air conditioners. The results were extraordinary. Students and teache...

We investigated possible relationships among pseudocoelomates (aschelminths) by using cladistic analysis to uncover all most-parsimonious trees from a data set comprising 45 morphological characters of 11 phyla (3 acoelomate, 7 pseudocoelomate, and 1 coelomate). Analysis of our matrix yielded 2 most-parsimonious trees, differing only in relative placement of 3 taxa (Kinorhyncha, Loricifera, and Priapulida). Tree topology suggests that the pseudocoel either evolved twice, or that it evolved once and was then independently lost in Gastrotricha and in Gnathostomulida. Tree topology also is consistent with derivation of the pseudocoel from a coelom. From our analysis and that of other morphologically-based studies, we conclude that there are 2 main lines of pseudocoelomate evolution: (1) a minor clade (Acanthocephala + Rotifera) defined principally by a syncytial epidermis, intracytoplasmic lamina, and sperms with anterior flagella; (2) a major clade (the 5 remaining phyla), defined primarily by a cuticle that is molted. Within the major clade are 2 subclades (Nematoda + Nematomorpha; Kinorhyncha + Loricifera + Priapulida). Using morphological data, the chief issues remaining to be resolved are placement of Gastrotricha and Gnathostomulida, and evolution of the pseudocoel. No analysis based solely on morphological data has so far produced a tree congruent with those based on molecular data. Nevertheless, there is a general consensus that (1) the pseudocoel is of little phylogenetic significance and (2) the pseudocoelomates are probably polyphyletic. Additional key words: evolution, phylogeny "In the face of this bewildering array of conflicting opinions about the interrelationships of the aschelminth phyla, it is impossible to form a coherent picture of the evolution of the animals." (Clark 1964) Does Clark's observation made some 30 years ago still offer a realistic view of our understanding of pseudocoelomate (aschelminth) phylogeny? Clearly, these vermiform taxa share interesting similarities. However, they also possess some striking differences, which have led many authors to choose not to include them in a single phylum, the Aschelminthes (e.g., Clark 1964; Anderson 1983; Inglis 1985; Pearse et al. 1987; Brusca & Brusca 1990; Kozloff 1990; Willmer 1990; Ruppert & Barnes 1994). In fact, for Inglis (1985) there is no common history at all, just completely independent solutions to similar evolutionary pressures. Further complicating the matter is Ruppert's (1991) view that calls into question the significance of 2 traditional characters that link the pseudocoelomates: pseudocoel and cuticle (see also Brusca & Brusca 1990). The alternative position, of course, argues for at least a loose relationship among some of these taxa (e.g., Hyman 1951; Boaden 1985; Lorenzen 1985; Sterrer et al. 1985; Bergstrom 1991; Meglitsch & Schram 1991; Malakhov 1994). The problem is to dissect possible relationships from what appears to be an intractable array of characteristics. However, there is no reason to abandon the logical search for phylogenetic relationships among these taxa. In fact, many workers have explored this field, with phylogenetic analyses that include most or all of the appropriate taxa (e.g., Lorenzen 1985; Meglitsch & Schram 1991; Schram 1991; Eernisse et al. 1992; Conway Morris 1994; Nielsen 1994; 1995; Neuhaus 1994; Winnepenninckx et al. 1995). Here we report our findings from a cladistic analysis of 45 morphological characters and 11 taxa (3 acoelomate, 7 pseudocoelomate, and 1 coelomate). We also compared trees yielded from this study to other published works. Thus, the purposes of this study were to assemble a useful set of light microscopical, ultrastructural, and biochemical characters on the pseudocoelomate taxa and to develop parsimonious cladograms (hypotheses) from those data. Such work may provide a useful foundation for the molecular data that are now forthcoming (e.g., Lake 1990; Brandl et al. 1992; This content downloaded from 157.55.39.30 on Wed, 20 Jul 2016 06:18:46 UTC All use subject to http://about.jstor.org/terms Phylogeny of pseudocoelomates Smothers et al. 1994; Garey et al. 1995; Winnepenninckx et al. 1995). A combination of morphological and molecular data may eventually lead to a comprehensive phylogeny of these taxa (cf. Hillis 1987; Patterson et al. 1993).

Colonies of Sinantherina socialis (phylum Rotifera) form conspicuous masses that should make them extremely vulnerable to fishes capable of ingesting small live prey (

We examined the nature and adaptive significance of substrate selection by larvae of the sessile rotifer Collotheca gracilipes. In a small artificial pond the preferred substrate was the anatomical undersurfaces (abaxial) of Elodea canadensis leaves, although four other macrophytes were present (Ceratophyllum demersum, Lemna minor, Myriophyllum spicatum, and Nymphaea odorata). Density of adults on Elodea at times reached >6 individuals/mm2, with >98% attached to abaxial surfaces. However, larvae offered plants in pairwise combinations selected substrates in the following order: Lemna > Elodea > Myriophyllum > Nymphaea. No larval loyalty to parental substrate was exhibited. Larvae preferentially selected abaxial over adaxial surfaces of Elodea leaves (91% on abaxial) in continuous illumination experiments, but the larvae did not discriminate between the two surfaces in total darkness (48% on abaxial). In the absence of a plant substrate, cell debris from any one of four aquatic and two terrestrial plant species induced larval settlement on the bottom of plastic well-depressions. Activity could not be attributed to carbohydrate, lipid, nucleic acid, or protein moieties within these extracts. However, alpha-amylase induced rapid larval settlement in the depressions. In the presence of this calcium chelator, larvae did not distinguish between ad- and abaxial leaf surfaces to the same degree as without the enzyme. Phospholipase-C and EDTA induced similar effects. Larval preference for abaxial surfaces could be reduced slightly when pH was stabilized at < 7.0. Because living Elodea in neutral-to-alkaline water can remove Ca+2 from beneath its leaves and release it from adaxial surfaces while photosyn- thesizing, we hypothesized that larvae initiate substrate selection activities on any surface when they are in microhabitats having ambient Ca+2 concentrations below a threshold concentration. Short- term, in vitro growth experiments showed that rotifers attached to abaxial surfaces of Elodea leaves grew significantly taller and produced more eggs per female than those which had been induced to settle on adaxial surfaces.

Larvae of the sessile rotifer Ptygura beauchampi begin substrate selection activities when they chemotactually sense a stimulus associated with the glandular tfichomes which cover their preferred substrate, the trap door region of the largest, prey capturing organs of the carnivorous aquatic plant, Utricularia vulgaris. Four other co-occurring congeneric species (U. gibba, U. inflata minor, U. intermedia, and U. purpurea) and 2 smaller, morphologically distinct, trap types of U. vulgaris were not colonized. All of these Utricularia traps (except U. purpurea) have glandular trichomes which are nearly indistinguishable from one another. The stimulus appears to be chemical in nature, arising from the terminal head cells of trichomes as they develop. The chemical stimulus (an allelochemic agent) may be the utricularian prey-lure first proposed by Cohn in 1875. This symbiotic relationship should be termed commensal because rotifers colonize, but do not feed on the plant or its prey, and because the plant is apparently not affected by the colonization.

A new approach to transducer design is introduced in which a transducer is viewed as a continuum of infinitesimal, locally reacting elements. The transducer response is the coherent sum of the responses of the infinitesimal elements. Hence variations in transducer response characteristics will be produced by variations in the relative contribution of each element. It is thus possible to produce designed transducer characteristics through selection of a suitable local sensitivity shading function. This new approach is used to design a foil electret acoustic antenna which achieves with a single transducer direction characteristics similar to these of a linear microphone array. Five methods for accomplishing sensitivity variation in the electret microphone have been identified: variation of active width, variation of charge density, variation of actual airgap, variation of foil thickness, and variation of effective airgap. It is shown that compared to a linear microphone array, the single transducer acoustic...

A new touch actuator is described that consists of a single metalized foil electret, a number of independent metal backplate sections aligned with the holes of a front cover, and air gaps separating electret and backplate sections. The metal layer of the foil forms a transducer with capacitance C a with each backplate section. The actuator is operated by touching the foil electret through one of the front-cover holes. For a trapezoidal displacement (duration 2T ) of the foil electret, the electrical output signal across a terminating resistor R consists of a pair of oppositely poled spikes with duration comparable to RC a , if RC a is smaller than T . If RC a is larger than T , the electrical output approximates the displacement. For an electret with a charge density of 10^{-8} C/cm^{2} , the measured pulse amplitudes due to touching are of the order of 0.3 to over 100 V depending on the applied force, and on the resistive and capacitive loading. The touch actuator is mechanically simple, reliable to use, inexpensive to produce, and can be made with an overall thickness of less than 0.5 cm. Apart from its potential use in telephone dials, it may also find applications as a key transducer in digital devices.

Clearance rates of three sessile and four free-swimming rotifer species from a small acid bog-pond were measured using in situ techniques. Three radioactively labeled cell types, an alga (Chlamydomonas), a bacterium (Enterobacter = Aerobacter), and a yeast (Rhodotorula) were used as tracers. Clearance rates (using yeast) ranged from 250 µ1 • animal-1 • h-1 depending on species. Ptygura crystallina, Ptygura pilula, Floscularia conifera, and an unidentified bdelloid ingested all three foods with substantial variation in clearance rates among species and cell type. There was an insignificant error (

Coloniality in the phylum Rotifera is defined and reviewed. Only two families of rotifers contain truly colonial forms: Flosculariidae and Conochilidae (order Gnesiotrocha, suborder Flosculariacea). Most species form intraspecific colonies ranging in size from a few to about 200 individuals, but species that produce enormous colonies (> 1 000 individuals) are also known. All seven genera of the Flosculariidae contain species that form colonies to widely varying degrees (Beauchampia, Floscularia, Lacinularia, Limnias, Octotrocha, Ptygura, Sinantherina). All four species of the monogenetic Conochilidae (Conochilus) are colonial, but two species form colonies of only an adult and a few young. At least one other family (Philodinidae; Bdelloida) contains a species that exhibits a form of coloniality (Philodina megalotrocha). Two hypotheses that attempt to explain the adaptive significance of coloniality (Energetic Advantage and Predatory Avoidance) are reviewed and new information concerning the former is presented. Evolution of coloniality is discussed briefly.

We investigated evolutionary relationships among orders in phylum Rotifera and among species in genus Notholca (Rotifera) by computing parsimonious cladograms. All of the most-parsimonious cladograms generated for the ordinal level confirm the view that class Monogononta, superclass Eurotatoria, and phylum Rotifera are monophyletic. Species within the genus Notholca were separated into six groups (clades), but some species have been defined based on highly variable characters not reliably studied using cladistics. Therefore, phenetic studies are warranted, especially for species possessing caudal processes.

The sessile rotifers are taxonomically defined as all the individuals belonging to the families Flosculariidae, Conochilidae (Order Flosculariaceae), and Collothecidae (Order Collothecaceae) (Edmondson, 1940, 1944). Freeswimming species are, however, found in each family. The Conochilidae are totally planktonic. Although most of my remarks in this review will concern those species which as adults are permanently attached to surfaces, complete understanding of the evolution of this group is not possible without considering the planktonic forms.

An acoustic transducer for producing highly directional characteristics comprises a metalized backplate (130) facing the flat surface (134) of an electrostatically charged electret foil (132). The thickness of the electret foil varies along the length thereof according to a predetermined relationship. The sensitivity of the electret transducer varies directly with the thickness of the electret foil.

The overall sensitivity of foil electret microphones has been shown to be independent of area [see G. M. Sessler and J. E. West, J. Acoust. Soc. Am. 40, 1433–1440 (1966)]. However, recent theoretical and experimental investigations have shown that within a single electret transducer, the sensitivity can be varied to affect directional response. Using sensitivity control, arrays of microphones can be replaced by a single transducer. In general, the single transducer is less affected by small errors in construction than its array counterpart.

An electret transducer for producing a directional response, electret foil (92) and a backplate (94) with the actual air gap thickness therebetween varying in accordance with a predetermined relationship. The sensitivity of the electret transducer varies inversely as the actual air gap thickness. In one embodiment the actual air gap thickness is realized by a plurality of posts (90) having heights varying according to the aforesaid relationship. In another embodiment, the actual air gap thickness is realized by varying the thickness of the aforesaid backplate.

A directional electret transducer comprises an electret foil and a metalized backplate the effective air gap thickness therebetween varying according to a predetermined relationship. The sensitivity of the electret transducer is directly proportional to the effective air gap thickness. The effective air gap thickness is realized in three ways: first, a plurality of equal diameter holes are drilled to varying depths in the aforesaid backplate; second, a plurality of holes of varying diameters are drilled through the aforesaid backplate; third, a plurality of equal diameter holes are drilled through the aforesaid backplate, the density of the holes varying. In each of the aforesaid three ways, the variation is according to the predetermined relationship.

ELECTRET TRANSDUCER WITH A SELECTIVELY METALIZED BACKPLATE Abstract An electret transducer comprises an electrostatically charged electret foil superimposed directly over a selectively metalized rough surface of a backplate. Selective metalization is realized by depositing a thin metal layer, the contour of which is defined by a predetermined relationship, over the rough surface. The sensitivity of the electret transducer at any point thereon is directly proportional to the width of the metal layer on the backplate. The response characteristic of the electret transducer comprises a main lobe and a plurality of sidelobes below a preselected threshold.

An electret transducer for producting a highly directional response characteristic comprises a backplate (18) and, superimposed thereon, an electrostatically charged electret foil (10). The electrostatic charge varies according to a predetermined relationship. The sensitivity of the electret transducer, at any point thereon, is directly proportional to the electrostatic charge on the electret foil at that point.

Background In spite of considerable efforts over past decades we still know relatively little regarding the biogeography of rotifers of inland waters in México. To help rectify this we undertook an extensive survey of the rotifer fauna of 48 water bodies in the Chihuahuan Desert of México. Results Of the sites surveyed, 21 had salinities ≥ 2000 μS cm-1 and in these we found 57 species of monogonont rotifers and several bdelloids. Species richness in the saline sites varied widely, with a range in species richness of 1 to 27 and a mean (± 1SD) = 8.8 (± 6.2). Collectively all sites possess relatively high percent single- and doubletons, 33.3 and 21.7%, respectively. Simpson's Asymmetric Index indicated that similarity in rotifer species composition varied widely among a set of 10 sites. These were selected because they were sampled more frequently or represent unusual habitats. These SAI values ranged from 0.00 (complete dissimilarity) to 1.00 (complete similarity). The Jaccard Index varied between 0.00 and 0.35. This observation probably reflects similarities and differences in water chemistry among these sites. Inland saline systems differed in their chemical composition by region. Conductivity was related to hardness and alkalinity. In addition, hardness was positively associated with chloride and sulfate. RDA showed that several species were positively associated with chloride concentration. Other factors that were significantly associated with rotifer species included the presence of macrophytes, nitrate content, oxygen concentration, TDS, latitude and whether the habitat was a large lake or reservoir. Conclusion This study illustrates the diversity of the rotiferan fauna of inland saline systems and the uniqueness among waterbodies. Conservation of these systems is needed to preserve these unique sources of biodiversity that include rotifers and the other endemic species found in association with them.

The main aim of this study was to investigate rotifer assemblages in the littoral zone of shallow lakes in two different climate zones in Europe and Asia, temperate and semiarid, respectively. To analyze the rotifer community structure, 4 shallow lakes in Croatia (45°57′37″ N, 15°50′63″ E) and 3 shallow lakes in Iran (3708'30'' N, 4513'26'' E) were compared along gradients of vegetation cover, trophic level and antrophogenic influence. We recorded higher rotifer diversity in temperate lakes, contrary to the lower diversity in the semiarid waters. In both climate zones, rotifer diversity increased with enhanced macrophyte coverage and decreased at higher trophic levels. Rotifer density positively correlated with trophic levels in both areas, as well as with elevated salinities in the semiarid waters. Remarkablely higher rotifer densities at increased salinity of semiarid climate were mirrored in domination of few species. According to the feeding guilds, microphagous species prevailed in all the investigated waters. Results of our study confirm that Brachionus rotifers are well-adapted to salinization and could be considered as susceptible indicators of environmental changes..It was also clarified that ecological drivers of rotifer diversity and density can have similar impacts even in distinct and independent ecosystems.

The intention of this study was to analyze rotifers contribution in lotic meiofauna of bryophytic habitats in karst running waters along the longitudinal profile of Plitvice Lakes (Croatia). We choose three hydromorphologically different sampling stretches: 1) a channel with low inclination ; 2) small cascade with low inclination and 3) a channel with cascades and sharp inclination. On each stretch we distinguished two microhabitats, fast and slow flow velocity. Rotifers, particularly bdelloids, and nematodes were established as most abundant meiofaunal groups in bryophytic microhabitats. The results of our study suggest that flow velocity, as main stressor of lotic habitats governed the differences of monogonont and bdelloid rotifers assemblage among the lotic stretches and between microhabitats. The positive correlation between bdelloid density and flow velocity explains their statistically significant higher density at high water currents. Food supplies, expressed through the ultra fine particulated organic matter, positively influenced on rotifers density as well on increasing population of other meiofaunal groups, i.e. nematodes. We connected bdelloids rheophilic tendency to their food preferences for ultra fine organic particles providing flourescent beads experiments. The results also indicate that bdelloids occupy bryophytic microhabitats with higher flow velocity as long bryophytes represent suitable surfaces and ensure constant inflow of higher food concentration.