New ultrastructural aspects of the spermatozoon of Aplysia depilans (Gastropoda, Opisthobranchia).
The spermatozoon of the sea hare Aplysia depilans was studied under scanning (SEM) and transmission electron microscopy (TEM). Previous descriptions of this sperm and related species, both from light and electron microscopy, were inconsistent with each other. These descriptions include A. depilans, A. punctata, A. fasciata, A. kurodai and Bursatella leachiplei. Several detailed micrographs provide a new ultrastructural model and reveal new aspects such as the presence of acrosome and the absence of a glycogen piece, therefore the modified dense ring is the terminal structure. Results also show that previous models are incorrect in many aspects. The spermatozoon is a long slender uniflagellated cell with a complex helical structure and a length of approximately 165 microm. Observed in SEM the spermatozoon has an undifferentiated head and tail. The nucleus is cord-shaped and helically intertwined with the axoneme/mitochondrial derivative complex. The mitochondrial derivative has only one glycogen helix. Glycogen presence was demonstrated by Thiéry's method. Typical heterobranchia spermatozoa features are recognised. From bibliographic analysis, a high degree of similarity was found with the sperm of Pleurobranchea maculata (Notaspidea).
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Department of Cell Biology, Institute of Biomedical Sciences, and Center of Marine and Environmental Research, University of Oporto, Portugal.
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Azevedo
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D000177:Acrosome / Q000648:ultrastructure; D000818:Animals; D001048:Aplysia / Q000502:physiology / Q000648:ultrastructure*; D002467:Cell Nucleus / Q000648:ultrastructure; D008297:Male; D008855:Microscopy, Electron, Scanning; D015388:Organelles / Q000648:ultrastructure; D013094:Spermatozoa / Q000648:ultrastructure*