Acanthocephala (thorny-headed worms) is a phylum of endoparasites of vertebrates and arthropods, included among the most phylogenetically basal tripoblastic pseudocoelomates. The phylum is divided into three classes: Archiacanthocephala, Palaeacanthocephala, and Eoacanthocephala. These classes are distinguished by morphological characters such as location of lacunar canals, persistence of ligament sacs in females, number and type of cement glands in males, number and size of proboscis hooks, host taxonomy, and ecology. To understand better the phylogenetic relationships within Acanthocephala, and between Acanthocephala and Rotifera, we sequenced the nearly complete 18S rRNA genes of nine species from the three classes of Acanthocephala and four species of Rotifera from the classes Bdelloidea and Monogononta. Phylogenetic relationships were inferred by maximum-likelihood analyses of these new sequences and others previously determined. The analyses showed that Acanthocephala is the sister group to a clade including Eoacanthocephala and Palaeacanthocephala. Archiacanthocephala exhibited a slower rate of evolution at the nucleotide level, as evidenced by shorter branch lengths for the group. We found statistically significant support for the monophyly of Rotifera, represented in our analysis by species from the clade Eurotatoria, which includes the classes Bdelloidea and Monogononta. Eurotatoria also appears as the sister group to Acanthocephala.

The Combined Effects of Food and Temperature on the Life History Parameters of Brachionus patulus MULLER (Rotifera) key worda: Rotifera, Brachionw patulus, food, temperature, life history parameters AbstractThe combined effects of different levels of temperature (15". 25" and 35 "C) and food Chlorella (1,2 and 4 x 106 cells/ml) on the life history parameters (lifespan, life expectancy, net reproductive rate, intrinsic rate of increase, developmental time, and generation time) of a laboratory population of the rotifer Brachionus patulua were investigated. Both food and temperature, independently and in interaction, significantly influenced nearly all the parameters. The reproductive performance was a direct function of the food level, but the magnitude of food effect was temperature-dependent. The observed temperature x food interaction effects are explained in terms of the energetics of resource apportionment between metabolism and reproduction. 252 226 226 229 231 231 232 235 235 237 238 238

Correspondence: J. Flores-BurgosIn the present work we tested the effect of Chlorella vulgaris and Scenedesmus acutus in different proportions on the population growth of Brachionus calyciflorus, Brachionus patulus, Ceriodaphnia dubia, and Moina macrocopa. In general, both rotifer species grew well on either type of algae. Regardless of algal mixture, B. calyciflorus had a shorter initial phase, while B. patulus needed more than a week to begin the exponential phase of growth. Both the rotifer species showed consistently better population growth with Chlorella than on Scenedesmus, or the mixture. At any given algal combination, B. patulus had higher peak values than B. calyciflorus.The rate of population increase (r) for both the rotifers varied from 0.18 to 0.48 d -1 depending on the algal type and combination. Regardless of algal type and combination, B. calyciflorus had a much higher value of r than B. patulus. Both C. dubia and M. macrocopa grew on the algal types, whether offered separately or in mixture. Regardless of the treatment type, C. dubia needed a longer period (about 2 weeks) than M. macrocopa to reach peak abundances. Thus, our study did not support the view that Scenedesmus is consistently superior to Chlorella as a basic diet to the tested species of zooplankton. Populationswachstum von Zooplanktern (Rotatorien und Cladoceren) bei Ernährung mit Chlorella vulgaris und Scenedesmus acutus in unterschiedlichen Anteilen Untersucht wird der Einfluss von Chlorella vulgaris und

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The combined effects of sublethal levels of DDT (0, 15, 30, 45, and 60 µg •1 -1 ) and food (Chlorella at 1 and 3 x 10 6 cells ml -1 ) on the demography of the rotifer Brachionus patulus were studied . The average lifespan, life expectancy, net reproductive rate (R 0 ) and intrinsic rate of increase (r) were significantly greater at the higher food level, but declined with increasing DDT concentration . A significant DDT food interaction was manifested in the toxicity-mitigating action of the higher food density at higher DDT levels . The r values were negative at DDT levels 30 µg .1 -1 and above, only when food density was low. The effective DDT concentration at which a given parameter value was reduced to 50% of that in the controls (EC50) was lower at lower food levels for both survivorship and reproduction, and lower for reproduction than for survivorship at either food level .