Spermatid and spermatozoon structure in fresh-water nematode Paractinolaimus microdentatus (Nematoda: Dorylaimida: Actinolaimidae)

摘要

The nematode spermatozoa have been studied in many nematode taxa including the order Dorylaimida. However, all information on the dorylamid spermatozoa is based on the representatives of only one genus, Xiphinema (Longidoridae). The structure of spermatids and spermatozoa from male gonads of the fresh-water dorylaimid Paractinolaimus microdentatus (Actinolaimidae) were studied using transmission electron microscopy (TEM). An unusual spindle-shaped complex of nucleus with mitochondria is characteristic for spermatids and immature spermatozoa. The complex contains the nucleus consisting of intertwining threads of chromatin without a nuclear envelope, a monolayer of mitochondria with dense matrix, and a fibre layer which encloses the mitochondria; in P. microdentatus the fibre layer has a distinct annulated structure. The peripheral cytoplasm of the spermatid contains large amount of filamentous matter filling prominent pseudopods. The immature spermatozoa are unpolarised 8-10 mu m long and 2 mu m wide cells with filopodia covering the cell surface. Each spermatozoon contains the central complex of nucleus and mitochondria, which is surrounded by electron-light cytoplasm containing numerous bundles of filaments and microtubule-like fibres 16-18 nm in diameter. No inclusions resembling membranous organelles specific of other nematode spermatozoa were observed in the male germ cells of P. microdentatus. The spermatozoa of the dorylaimids from two families, Longidoridae and Actinolaimidae show close resemblance both in structure and development. The spermatozoa of the dorylaimids studied have very special internal structure, which differentiates them from other nematode spermatozoa and may be considered as the distinct character of the order.