THE SPERM MORPHOLOGY OF THE EUPHAUSIID MEGANYCTIPHANES NORVEGICA (CRUSTACEA, EUCARIDA)

The sperm ultrastructure of Meganyctiphanes norvegica was examined wit h the aim of investigating phylogenetic relationships between Euphausi acea and Decapoda. A noticeable feature of the spermatozoon of M. norv egica is the presence of a thick, two-layered capsule that is in close contact with the plasma membrane. The sperm ultrastructure in this sp ecies appears to be similar to that of Euphausia sp., the only other e uphausiid investigated to date. The sperm of both euphausiids resemble those of some species of decapods in that they have a loose central c hromatin surrounded by the cytoplasmic ring and lack an acrosome, nucl ear envelope and radial arms. These features are suggested to represen t eucarid plesiomorphic characters.