Sperm ultrastructure of the deep-sea hydrothermal vent octopod Vulcanoctopus hydrothermalis has been carried out by transmission electron microscopy. Spermatozoa of this species have the shortest head observed so far in octopodids. The acrosome possesses a helix with six gyres. The rod-shaped nucleus is short and wide in relation with other octopodids. Noteworthy features along the nucleus are the regularly disposed dense bands of cytoplasm, which have not been observed before in octopodids. The nuclear fossa is very short and wavy. Mitochondrial sheath has 10 elongated mitochondria running parallel to the axoneme-coarse fibers complex. Sperm morphology of V. hydrothermalis resembles that of Enteroctopus dofleini, suggesting a close phylogenetic relationship. J. Morphol. 271:932–936, 2010. © 2010 Wiley-Liss, Inc.