Two malaria parasites (Apicomplexa : Plasmodiidae) of the Australian skinkEgernia stokesii

The Australian skink Egernia stokesii is parasitized uncommonly by Plasmodi um circularis n. sp, and by Plasmodium mackerrasae. Plasmodium circularis i s distinguished from all other plasmodiids by immature schizonts that encir cle host cell nuclei, forming an unbroken ring from apparent fusion of the attenuated ends. Mature schizonts contract into halteridial or dumbbell-sha ped forms 15.6 x 4.3 mu m, LW 66.2 mu m(2), with 19-52 nuclei. Rounded or o val gametocytes are 9.0 x 7.3 mu m, LW 66.9 mu m(2), and L/W 1.24. Gametocy te LW is 2.63x host erythrocyte nucleus size and 1.79x uninfected erythrocy te nuclei. Plasmodium mackerrasae occurs in high prevalence and often massi ve parasitemia in E. stokesii. Schizonts, often oblong, elongate. or oval. are 5.1 x 3.7 mu m, LW 19.8 mu m(2), with 7.2 merozoites. Immature gametocy tes, elongate with terminal nucleus, may produce multiple infections of 6 o r more parasites. Mature gametocytes, usually rounded, are 5.8 x 4.6 mu m, LW 26.7 mu m(2), and L/W 1.29. Gametocyte size is 0.98x host erythrocyte nu cleus size and 1.03x uninfected erythrocyte nuclei. Phanerozoites, in endot helium or connective tissue of most organs, may appear in large numbers in circulating blood as seemingly intact bodies of regular form, similar to or larger than phanerozoites seen in sections. Previously unreported phenomen a for hemosporidian parasites include extremely large, highly irregular exo erythrocytic schizonts, in circulating blood, perhaps torn from endothelial lining of blood vessels and sinuses, and a visible flooding of free merozo ites into the blood stream.