The sperm morphology of the euphausiidMeganyctiphanes norvegica(Crustacea, Eucarida)

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Abstract
The sperm ultrastructure of Meganyctiphanes norvegica was examined with the aim of investigating phylogenetic relationships between Euphausiacea and Decapoda. A noticeable feature of the spermatozoon of M. norvegica is the presence of a thick, two-layered capsule that is in close contact with the plasma membrane. The sperm ultrastructure in this species appears to be similar to that of Euphausia sp., the only other euphausiid investigated to date. The sperm of both euphausiids resemble those of some species of decapods in that they have a loose central chromatin surrounded by the cytoplasmic ring and lack an acrosome, nuclear envelope and radial arms. These features are suggested to represent eucarid plesiomorphic characters.