In this study, the sperm morphology of the parasitoids Trichospilus diatraeae and Palmistichus elaeisis (Eulophidae) was investigated using light and transmission electron microscopy. In the two species, the sperm are spiral along their entire length and measure about 130. μm and 195. μm in length, respectively. The head region consists of the acrosome and nucleus. The acrosome is composed of an acrosomal vesicle and, in P. elaeisis, a perforatorium. In both species, an extracellular layer in which several filaments are radiated covers the acrosome and the anterior nuclear region. The nuclei are filled with homogeneous and compact chromatin and measure about 50. μm in length in P. elaeisis and 20. μm in T. diatraeae. The flagellum consists of an axoneme with the 9. +. 9. +. 2 microtubule arrangement spiraled in a long helix, two mitochondrial derivatives coiling around the axoneme and, in P. elaeisis, two accessory bodies. 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