Ultrastructure of Cochlosoma anatis Kotlán, 1923 and taxonomic position of the family Cochlosomatidae (Parabasala: Trichomonadida)

Abstract

Summary The fine structure of Cochlosoma anatis is described from scanning and transmission electron microscopy. These flagellates are asymmetrical and uninucleate, with a conspicuous adhesive disc formed from the modified pelta. Six flagella arise from the anterior end. Four of them emerge anterolaterally from the lateral groove. The fifth flagellum is recurrent and adheres to the cell body by a well developed undulating membrane, formed by a cytoplasmic fold with the marginal lamella. The kinetosome of the recurrent flagellum is situated at an angle to the kinetosomes of the anterior flagella. This kinetosomal complex is associated with fibrillar appendages characteristic of a trichomonad mastigont. The kinetosome of the sixth flagellum is located outside the complex of the other kinetosomes, on the dorsal side of the protozoan body. The undulating membrane is supported by the prominent costa with Type B periodicity and passes throughout the lateral groove extending to the end of the parasite’s body. There is a parabasal apparatus composed of a Golgi complex and a single parabasal fiber. The axostyle, formed from a single layer of microtubules, passes through the body, protruding caudally in a short projection. Anteriorly it overlaps the inside of the pelta. An extranuclear mitotic spindle is formed during the nuclear division. The cytoplasm contains double membrane bound organelles similar to hydrogenosomes. These observations show high degree of homology of Cochlosoma with Trichomonadida Kirby, 1947 warranting inclusion of the family Cochlosomatidae Tyzzer, 1930 into this order.