ULTRASTRUCTURE OF THE MATURE SPERMATOZOON OF THE KING CRAB LITHODES MAJA (LITHODIDAE, ANOMURA, DECAPODA) - FURTHER CONFIRMATION OF A LITHODID-PAGURID RELATIONSHIP

Ultrastructure of the spermatophore and spermatozoon of the king crab Lithodes maja is described and illustrated, The spermatophore is a ped unculate structure of which the major components are the sperm-filled ampulla, stalk, pedestal, and a smaller accessory ampulla at the base of the main ampulla. Each spermatozoon features a subspherical, concen trically zoned acrosomal vesicle, capped by a centrally perforate oper culum and posteriorly embedded in the cytoplasm, and a large globular nucleus. Three microtubular arms emerge from the cytoplasm below the a crosomal vesicle. The spermatophores and spermatozoa share many featur es with those of their nearest postulated relatives-members of the Pag uridae (the genus Pagurus in particular), Spermatophore characters tha t link L. maja with pagurids are the presence of the accessory ampulla (synapomorphy, also with the parapagurids) and the homogeneous granul ar nature of the spermatophore wall. Sperm characters include the simp le concentric zonation of the acrosomal vesicle, the shape and differe ntiation of the operculum (synapomorphic with Paguridae), the electron -dense plume in the base of the acrosomal chamber (synapomorphy with P agurus), and absence of microvillar projections in this chamber. Sever al features in which L. maja differs from species in the genus Pagurus include the central perforation in the operculum, the absence of reti culated acrosome zones, and indications of an irregular flange in some planes of the acrosomal vesicle (possible autapomorphy).