Species of the cnidarian genus Henneguya Thélohan, 1892 (Myxosporea: Myxobolidae) are histozoic parasites commonly found in freshwater and, more rarely, in marine fish. The development of these parasites in fish tissues includes the formation of plasmodia within which occurs the sporogony originating spores with two caudal processes, which are usually randomly distributed within the plasmodia. In this report the authors present some cases of non-random distribution of the spores of six species of Henneguya within their plasmodia. Two different patterns of non-random distribution were found based on a literature survey. These patterns and their origin are discussed. Apparently this non-random distribution of the spores is due to both internal and external factors.

Departamento de Biologia Animal Instituto de Biologia Universidade Estadual de Campinas Brasil

Departamento de Biologia Faculdade de Ciencias Universidade do Porto Portugal; Centro Interdisciplinar de Investigacao Marinha e Ambiental Matosinhos Portugal

Departamento de Ecologia e Biologia Evolutiva Universidade Federal de Sao Paulo Diadema Sao Paulo Brasil

Institute for Veterinary Medical Research Centre for Agricultural Research Hungary; Hungarian Academy of Sciences Budapest Hungary

Laboratorio de Engenharia Matematica Instituto Superior de Engenharia do Porto Portugal

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Solving the Myxidium rhodei (Myxozoa) puzzle: insights into its phylogeny and host specificity in Cypriniformes