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Spermatozoal morphology of the anomuran crab Cervimunida johni was investigated using scanning and transmission electron microscopy. The spermatozoon has an elongate shape and exhibits a total length of 22.7 mu m with a maximum width of 4.4 mu m. Three parts can be distinguished: (1) the elongate-ovoid acrosome located anteriorly, measuring 7.7 mu m in length and 2.7 mu m in width; (2) the cytoplasmic region, 3.0 mu m in length and 1.5 mu m in width; and (3) the nuclear region measuring 11.9 mu m in length and 4.4 mu m in width. The acrosome is composed of a thick electron-dense wall and a less electron-dense subacrosomal space showing actin-like filaments. The cytoplasmic region connects the acrosome with the nucleus, and three arms filled with microtubules arise from this region. The cytoplasm contains irregular mitochondria. The elongate nucleus has uncondensed DNA, its outer surface is highly folded and shows three principal longitudinal grooves. The microtubular arms are located in these three nuclear grooves when the spermatozoa are inside the spermatophore, and extend laterally when they are placed in seawater. The spermatozoon of C. johni follows the general pattern described for other anomuran decapods.