Abstract
During development of the spermatid, two free flagella are transported distally from the main spermatid mass by elongation of the shaft. They rotate back towards the shaft and lie parallel with it prior to fusion in a distal-proximal direction. This process conforms to that found in other free-living platyhelminths that have fused or adjoined axonemes in their sperm (Acoela, Kalyptorhynchia, Polycladida). It is basically different from the process of fusion in the majority of neodermatan species (major groups of parasitic platyhelminths), where the attachment of axonemes remains near the main spermatid body, a median process grows out between them, the nucleus and mitochondria migrate into this process and axonemes then fuse with it in a proximal-distal manner.Pterastericola astropectinis also differs from the Neodermata in the presence of dense bodies in the sperm. The ultrastructure of the sperm, spermiogenesis and protonephridia does not support the view of a close affinity between Pterastericolidae and Neodermata.
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Watson, N.A., Rohde, K. & Jondelius, U. Ultrastructure of sperm and spermiogenesis ofPterastericola astropectinis (Platyhelminthes, Rhabdocoela, Pterastericolidae). Parasitol Res 79, 322–328 (1993). https://doi.org/10.1007/BF00932189
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DOI: https://doi.org/10.1007/BF00932189