Ref ID : 4091
Guy Brugerolle and Jean-Pierre Mignot; [Caracteristiques Ultrastructurales de I'Helioflagelle Tetradimorpha (Hsiung) et leur Interet pour l'Etude Phyletique des Heliozoaires]. J.Protozool. 30(3):473-480, 1983
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This freshwater species of Tetradimorpha has a spherical body with four flagella and radiating axopods; it transforms into a pear-shaped cell that anteriorly has four flagella intercalated between four axopods and posteriorly has six to eight divergent axopods. Ultrastructural study reveals an axopodial cytoskeleton of the centrophelidan type comprising an homogeneous lenticular centroplast which acts as MTOC for axopodial microtubules. A second skeletal element is a microtubular linkage between the kinetosomes and the axonemes of anterior axopods. A microtubule embedded in dense material diverges from near the base of each kinetosomes and parallels the distal portion of the axoneme of each anterior axopod. A microfibrillar envelope around the centroplast links the axopodial bases to the kinetosomes situated just above. Close to the centroplast, microfibrillar strands link the axopodial axonemes to the kinetosomes. Axopodial axonemes are composed of 5 to 30 microtubules irregularly arranged except for some that form equilateral triangles. The nucleus containing a central nucleolus is constrained within a cone formed by the axonemes of the posterior axopods and surrounded by dictyosomes. By the cytoskeletal organization, the structure of kinetocysts, and flagella without tubular mastigonemes, Tetradimorpha differs obviously from Ciliophrys marina. As Davidson (1975) predicted, Tetradimorpha is an intermediate link in the centrohelidan lineage; however, it lacks the characteristics of chrysomonads, the supposed ancestors of Heliozoa. The contribution of this genus to the study of the differentiation and the evolution of the cytoskeleton is also presented and discussed.