Fine structure of scorpion spermatozoa (Buthus occitanus; buthidae, scorpiones)

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Abstract
The mature spermatozoa of Buthus occitanus are threadlike in shape and divided into sperm head, middle piece, and end piece. The sperm head is corkscrew shaped anteriorly and in this region bears an unusual acrosomal complex consisting of a ring‐shaped acrosomal vacuole associated with a subacrosomal filament and a perinuclear amorphous component. The subacrosomal filament extends posteriorly into a tube‐like invagination of the elongated nucleus. The middle piece is characterized by elongated mitochondria which spiral around the anterior part of the flagellum in an extended collar separated from the flagellum by an extracellular cleft, termed the central flagellar tunnel. In addition to the usual 9 × 2 + 2 axonemal pattern in flagella, 9 × 2 + 1 and 9 × 2 + 3 patterns also were observed. The end piece is represented by the free flagellum. Similarities and diversities of scorpionid spermatozoa are discussed with respect to systematic relationships.