Evidence of antiparallel sperm bundles and limited sperm production in adult males of Phaleria testacea Say, 1824 (Tenebrionidae, Diaperinae).

In this study, we investigated the male reproductive system and sperm morphology of Phaleria testacea using both light and transmission electron microscopy. Our findings revealed important testicular features, such as the antiparallel arrangement of sperm in the testicular cysts, limited sperm prodution in adult males, defective spermatozoa, and bodies of cellular membranes in deterioration. We also observed more spermatids per cyst than in most Tenebrionoidea. The presence of vesicular bodies and defective spermatozoa may be linked to the species' environmental factors. Ultrastructurally, P. testacea spermatozoa display, in cross-section, rounded accessory bodies and a flattened nucleus and acrosome, the latter with two layers, and the flagellar elements like other tenebrionids. This study provides valuable information for understanding the reproductive biology of P. testacea and the sperm morphology in Tenebrionidae, along with their phylogenetic implications.