Intraspecific variability of Brachionus plicatilis

An extensive study of frontal margins of the lorica of Brachionus plicatilis was undertaken in an attempt to define its variability within this species. Specimens from mass cultures and from the natural environment were examined.     

Occurrence of Rotifera in the field user natural and intentionally-changed conditions. II. Lake Numasawa

Seasonal and vertical occurrences of representative rotifer species were recorded together with such taxa as Cyanophycea, Phytomastigophorea, Bacillariophycea, Protozoa, Rotifera and Crustacea, from 1982 to 1986 at two sites S1 (natural) and S2 (nearby water circulated since 1952). 1) The following species were observed from S1: K. hiemalis, C. ovalis, N. labis, L. patella and Anuraeopsis sp., from S2: B. urceolaris and A. ecaudis, 2) P. hudsoni appeared in 1984 as a successor to P. truncatum, 3) K. longispina was negatively associated with P. t. vulgaris, 4) Synchaeta spp suddenly appeared at both sites in 1985, 5) K. cochlearis, B. calyciflorus, Proalides sp., Diurella sp., N. labis, B. urceolaris and bdelloids did not appear until 1986, 6) The following species decreased or disappeared: A. p. herricki and Collotheca sp. since 1982, C. coenobasis, C. hippocrepis and K. hiemalis since 1984, 7) A complicated relation was observed between rotifer population density and other plankton. 8) Occurrence of Rotifera seemed to be affected by circulation of an electric power plant.     

Comments on the antarctic Rotifera

The Southern and Western water of L. Kyoga is characterised by low mean alkalinities, 1.23±0.08 m eq 1^-1; conductivities, 106±5 µS cm^-1; pH, 7.2±0.2 and high transparencies, 1.7±0.3 m. In the east, comparatively high alkalinities, 1.96±0.34 m eq 1^-1; conductivities, 168±21 µS cm^-1; pH of 7.4±0.2 and low transparencies, 0.8±0.2 m are encountered. Hardness varies as closely as alkalinity from 0.6±0.1 m eq 1^-1 in the west to 1.0±0.2 m eq 1^-1 in the east. SiO₃·Si and SO₄·S decrease westwards from the eastern lake arms, while NO₃·N and PO₄·P vary seasonally in the lake, which is mostly saturated with oxygen (86–120%) from the surface to the bottom. Some evidence of polymixis was encountered.A rich plytoplankton flora occurred with the major groups well represented. Chlorophyceae (37%), Bacillariophyceae (36%) and Cyanophyceae (26%). Synedra spp. (20%). Anabeana spp. (16°10), Nitzschia spp. (10%) were the dominant species groups during July–August 1981. The macrophyte genera Vallisneria, Potamogeton, Nymphaea, Ceratophyllum, Hydrilla occur prominently in the clearer southern lake water. Rotifers and Crustacean Zooplankters found are also recorded. Meroplanktonic crustaceans, chironomids and insects often occur in large numbers.     

Occurrence of Rotifera in the field under natural and intentionally-changed conditions

A comparison of population dynamics of rotifers under natural conditions with those under intentionally-changed ones was carried out at one Lake and five outdoor pools. In Lake Numasawa, dominant rotifers under natural conditions for the past two years were Polyarthra trigla vulgaris, Kellicottia longispina, Ploesoma truncatum, Asplanchna priodonta and Filinia longiseta. Keratella hiemalis, K. cochlearis, K. valga tropica, Brachionus caudatus and Ascomorpha saltans appeared sporadically. Three months after the start of circulation of part of the lake water by a water power plant no remarkable changes were observed as far as the seasonal and vertical distribution of dominant rotifers are concerned. In five pools with different kinds and ratios of covering by such macrophytes as Eichornia and Lemna or reed screen, three types of rotifer communities were found. Type I: Liliferotrocha sp., Brachionus calyciflorus, (B. budapestinensis), B. angularis, K. valga tropica, etc., in which both densities and frequencies were generally reduced in proportion to the ratio of covering either with macrophytes or reed screens. Type II: Filinia longiseta, Polyarthra trigla vulgaris, Asplanchnella sieboldi, etc. in which densities and frequencies were increased by covering either with macrophytes or reed screens. Type III: Trichocerca pusilla, B. quadridentatus, B. leydigi rotundus, Scaridium longicaudum, Euchlanis dilatata, Dicranophorus sp., etc, in which no precise correlation was found between occurrences of the Rotifers and ratio of covering.     

Notholca dongtingensis (Rotifera: Monogononta: Brachionidae), a new species from Dongting Lake,China

Notholca dongtingensis n.sp. was found in the second largest lake of China, Dongting Lake. It is related to Notholca labis Gosse, 1887 and N. kozhovi Vassilijewa & Kutikova, 1969. Its main distinguishing taxonomic features are a square-oval lorica, very short anterior spines, anterior lateral spines curving outwards and protrusile posterior margin of the ventral plate. This revised version was published online in July 2006 with corrections to the Cover Date.