Rotifera from Burundi: the Lepadellidae (Rotifera: Monogononta)

We studied the distribution of Lepadellidae (Rotifera) in freshwater habitats in the floodplain of the River Rusizi in northwest Burundi. Twenty-three species belonging to ColurellaBory de St. Vincent, 1824 (3 species), Lepadella Bory de St. Vincent, 1826 (18 species) and Squatinella Bory de St. Vincent, 1826 (2 species) are recorded, 22 of them are new to Burundi. One of the taxa encountered probably represents an unnamed species. Lepadella arabicaSegers & Dumont, 1993 is recognised as junior subjective synonym of Lepadella eurysterna Myers, 1942 (syn. nov.). Most of the taxa recorded are cosmopolitan or tropicopolitan, two are restricted to the tropical regions of the Old World and Australia, and one, Squatinella lunata Segers, 1993 is an Ethiopian endemic.     

Precopulatory mate guarding in Harpacticella inopinata Sars (Copepoda: Harpacticoida) from Lake Baikal

Precopulatory mate guarding is reported for the first time from a freshwater harpacticoid, Harpacticella inopinata. Adult males were observed grasping onto juvenile females from the third copepodid stage onwards, but most commonly with the fifth copepodid. This behaviour is interpreted as a plesiomorphic trait of the family Harpacticidae.     

Precopulatory and mating behaviour in the tasmanian bettongBettongia gaimardi desmarest (Marsupialia: Potoroidae)

Intersexual interactions in Tasmanian bettongs (Bettongia gaimardi) were observed in dyadic combinations. Several behaviours were associated with agonistic confrontations and occurred in predictable response sequences. There was no evidence of a consort period between males and pre-oestrous females. Overt sexual interactions occurred only on the night of oestrus, coincidentally with the maintenance of close spatial proximity. During copulation, multiple intromissions were regularly achieved but the intervals between successive bouts of these acts generally increased. Males were also observed to engage in regular attempts at social (urogenital) investigation and were apparently able to detect the reproductive state of all resident females, presumably utilising olfactory cues. The brevity of sexual interactions occurring between individuals contrasts with the more complex repertoire of the gregarious large macropodoid marsupials.     

A novel adhering junction in the apical ciliary apparatus of the rotifer Brachionus plicatilis (Rotifera, Monogononta)

Cultures of the rotifer Brachionus plicatilis were examined with regard to their interepithelial junctions after infiltration with the extracellular tracer lanthanum, freeze-fracturing or quick-freeze deepetching. The lateral borders between ciliated cells have an unusual apical adhering junction. This apical part of their intercellular cleft looks desmosome-like, but it is characterized by unusual intramembranous E-face clusters of particles. Deep-etching reveals that these are packed together in short rows which lie parallel to one another in orderly arrays. The true membrane surface in these areas features filaments in the form of short ribbons; these are produced by projections, possibly part of the glycocalyx, emerging from the membranes, between which the electron-dense tracer lanthanum permeates. These projections appear to overlap with each other in the centre of the intercellular cleft; this would provide a particularly flexible adaptation to maintain cell-cell contact and coordination as a consequence. The filamentous ribbons may be held in position by the intramembranous particle arrays since both have a similar size and distribution. These contacts are quite different from desmosomes and appear to represent a distinct new category of adhesive cell-cell junction. Beneath these novel structures, conventional pleated septate junctions are found, exhibiting the undulating intercellular ribbons typical of this junctional type, as well as the usual parallel alignments of intramembranous rows of EF grooves and PF particles. Below these are found gap junctions as close-packed plaques of intramembranous particles on either the P-face or E-face. After freeze-fracturing, the complementary fracture face to the particles shows pits, usually on the P-face, arrayed with a very precise hexagonal pattern.     

Size-related mating and mate guarding in the orb-web spiderNephila clavata (Araneae,Araneidae)

The orb-web spiderNephila clavata satisfies three conditions for assortative mating proposed by Ridley (The Explanation of Organic Diversity. The Comparative Method and Adaptations for Mating, Clarendon, Oxford, 1983); (1) a large male advantage in male-male competition, (2) a correlation between female size and fecundity, and (3) a long pairing duration. To test Ridley's hypothesis, size assortative mating and guarding were examined in the field. When data were pooled over time, assortative mating was found but this was due to temporal covariation of body sizes of males and receptive females. After controlling for the effect of time, size assortative guarding was not detected, although females guarded by males were larger than those not guarded in the early breeding season. Possible reasons for the absence of size assortative guarding were discussed.     

Ultrastructure and function of the mastax in Dicranophorus forcipatus (Rotifera: Monogononta)

Rotifers are characterized by a complex set of cuticularized jaw elements in the pharynx. The fine structure of the jaw elements has been the subject of SEM studies for some time, but only very limited information exists on the ultrastructure of the jaw elements and their function beyond taxonomic considerations. Drawing on SEM and TEM techniques, the present study presents a detailed analysis of the mastax in Dicranophorus forcipatus, a carnivorous monogonont rotifer species from freshwater habitats characterized by an extrusible, grasping jaw apparatus. Based on ultrathin serial sections, the jaw elements are reconstructed and, in total, nine paired and two unpaired muscles identified. Possibly homologous muscles in other rotifer species are discussed and functional considerations of the forcipate mastax are suggested.     

On Lecane tanganyikae new species (Rotifera: Monogononta, Lecanidae)

A new species of rotifer, Lecane tanganyikae n.sp., is described from the littoral of Lake Tanganyika and some water bodies in the plain of the Rusizi river near Lake Tanganyika, Bujumbura Province, Burundi. The affiliation of the new species, especially in relation to L. elsa Hauer, is discussed.     

On a new species of Keratella (Rotifera: Monogononta: Brachionidae)

A new species of planktonic rotifer, Keratella sinensis n.sp.is described from Lake Yaoquan, Heilongjiang, P.R. China. Itprobably also occurs in the Republic of Korea and Japan. The newmorphospecies is characterised by an unusually smooth lorica, andstrongly reduced lateral anterior spines. It is the first exampleof a planktonic freshwater rotifer, endemic to North EastAsia.     

Distribution of Brachionidae (Rotifera,Monogononta) in Inner Mongolian Waters

Two-hundred and fourty-six freshwater and saline-alkaline waters in Inner Mongolia, P.R. China were surveyed for Brachionidae. Twenty-nine brachionid morphospecies (33 taxa) are recorded, four are new to China. Some data on their distribution, and comments on selected taxa are provided. Brachionus asplanchnoides (stat.nov.) is reinstated at the morphospecies level. We suggest that this taxon may be used in aquaculture, considering that, by its large size, it extends the size range of brackish-water Rotifera potentially available as food for fish larvae.     

102+ rotifer species (Rotifera: Monogononta) in Broa reservoir (SP., Brazil) on 26 August 1994, with the description of three new species

The monogonont Rotifera fauna of Lobo (Broa) reservoir (SP., Brazil), present in 12 samples collected on a single date during the cool season (26 August 1994), is listed and commented upon. In total, 102 species could be identified, three of which, Ascomorpha tundisii n.sp., Lecane broaensis n.sp. and Lepadella neglecta n.sp. are new to science. Lecane mitis Harring & Myers and Lepadella elongata Koste are redescribed. A note on the taxonomy of the Ascomorpha saltans-group is added.     

Rhinoglena frontalis (Rotifera,Monogononta): a scanning electron microscopic study

Females and males of Rhinoglena frontalis (Monogononta, Epiphanidae) are observed by SEM and their external morphologies are compared. The two sexes differ in size and shape of the body. The female body is fusiform with a short, conical foot, while the male body is more slender and has a rather long foot. The rotatory apparatus (or corona) of both sexes is similar with only minor differences and consists of rows and tufts of cilia arranged around the mouth opening. The corona is made of two paired lobes lateral to the mouth and of a third prominent dorsal lobe, usually called proboscis. The three lobes are lined externally by dense rows of cilia, which constitute the cingulum, used for swimming. The central surface of the proboscis is covered with numerous longitudinal rows of cilia bent towards the mouth. The lateral lobes show, on their central surfaces, two concentric arcs of cirri (made of tightly packed cilia) bent towards the mouth. The similar organization of the rotatory apparatus of both sexes is related to the fact that the male, in this species, is able to feed and has a developed mastax and digestive system. The trophi of both sexes are illustrated and compared.     

Cryptic speciation in the cosmopolitan <Emphasis Type=Italic>Epiphanes senta</Emphasis> complex (Monogononta,Rotifera) with the description of new species

The phytoplankton species composition and seasonal succession were examined in Lake Kastoria during the period November 1998–October 1999. A total of 67 species and 19 functional groups were identified. Only 4 out of the 67 species, all Cyanobacteria, were dominant (Limnothrix redekei, Microcystis aeruginosa, Cylindrospermopsis raciborskii and Aphanizomenon gracile). Diatoms were rare, not only in terms of species number, but also in terms of biomass (contributing <5% to the total phytoplankton biomass) in relation to the rather low silicon concentrations throughout the year. The functional groups S1, S_N, M and H1 were found dominant in the lake. The species A. gracile (functional group H1) behaved like the species Cylindrospermopsis raciborskii (functional group S_N) which is tolerant to mixing and poor light conditions. The phytoplankton seasonal succession showed similar patterns in all six sampling stations, both at the surface and the bottom water layer, with minor differences during Microcystis aeruginosa dominance. Two steady-state phases were identified within a year lasting for 4 months under relatively stable physical conditions. In these steady-states, the Limnothrix redekei persistent dominance under low light availability and low inorganic nitrogen has been explained by its specific ability such as buoyancy regulation to exploit resources in the water column. Moreover, high population densities over the winter and before the development of daphnids may contribute to the steady-state dominance of Limnothrix. Different niches separated vertically in the water column is one of the explanations for the Limnothrix–Microcystis steady-state when a replacement between the two species was observed in different water layers and areas of the lake. Long lasting steady-states of Cyanobacteria observed in Lake Kastoria and in other Mediterranean and tropical freshwaters may indicate influence of warm climate properties on phytoplankton dynamics. Electronic Supplementary Material Supplementary material is available to authorized users in the online version of this article at http://dx.doi.org/10.1007/s10750-006-0360-4 Handling editor: K. Martens     

The Spermatozoon of Brachionus plicatilis(Rotifera,Monogononta) With Some Notes on Sperm Ultrastructure in Rotifera

The spermatozoon of B. plicatilisis a thread–like cell with an anterior flagellar portion and a posterior cell body. The flagellum has a lateral ‘undulating membrane’, containing a folded longitudinal cisterna and an axoneme. The basal body of the axoneme is at the anterior tip. The axoneme lacks outer dynein arms and extends through the entire flagellar region and most of the cell body. The main portion of the flagellum and of the cell body contains a series of vesicles with tightly packed tubules that may serve as a cytoskeleton. The cell body contains a partly condensed nucleus, several mitochondria and some cytoplasm. Some elongated mitochondria are arranged in the postnuclear region. When the spermatozoon moves, the undulations propagate from the basal body at the flagellar tip. Late spermatids can be recognized by the nucleus and the flagellum being coiled and enclosed within a common cell membrane. As in other rotifers, there are cigar–like cell products (‘rods’) in the testes. The general organization of the cell, including the absence of an evident acrosome, resembles that of the other known monogonont sperm types.     

Acute toxicity tests on three species of the genus Lecane (Rotifera: Monogononta)

Three rotifer species, Lecane hamataL. luna, and L. quadridentata, were submitted to acute toxicity tests to compare their susceptibility to 11 toxicants. In acute tests with 48-h exposure of neonates of less than 24 h old, copper was most toxic with LC₅₀ values in the range of 0.06–0.33 mg l^–1, while acetone was the least toxic with LC₅₀ values in the range of 5000–7000 mg l^–1. Differences in LC₅₀ value of up to 22-fold were found in the susceptibility to lead between the three species. These data indicate large differences in toxicity among members of the same genus, and point out that it is necessary to submit several species to toxicity tests in order to assess the potential effects of toxicants to rotifers. The commonly used Brachionus calyciflorus cannot be considered representative of all freshwater rotifers in this respect.