Ultrastructure of penetrated spermatozoa, ovary, and oogenesis ofDactylopodoola baltica(Gastrotricha, Macrodasyida)

Summary Penetrated spermatowa, ovary, and oogenesis of the macrodasyidan gastrotrich Dactylopodola baltica are described by means of transmission electron microscopy. The sperm consists of a rod-like nucleus and an adjacent region where a series of single mitochondria alternate with dark zones where dense bodies are located. Every spermatozoon is surrounded by a sperm enveloping membrane. The paired ovaries he on the left side of the animal. The oocytes are surrounded by an incomplete cover of wall cells. In the fiontal-most oocyte, electron-dense yolk granules and lipid droplets can be found and an egg envelope has developed. More caudally, spermatozoa penetrating into the oocytes are visible. Only the caudal-most bundles of young oocytes are not fertilized.