Description of the male reproductive apparatus of the hermit crab <i>Calcinus tubularis</i> (Decapoda: Anomura: Diogenidae)

Abstract

We describe for the first time the male reproductive apparatus, spermatophore and sperm of Calcinus tubularis, analysing them under interference phase microscopy, scanning electron microscopy and transmission electron microscopy. The testes merge into a tubular duct made up of four zones. In the proximal zone, the ampulla of the spermatophore starts to be formed. In the medial zone, the ampulla is completed, the stalk lengthens and the foot develops. The two halves making up the ampulla meet at the lateral ridge, which shows a mostly fibrillar ultrastructure. Spermatozoa are composed of an almost spherical acrosomal vesicle, capped by a conical operculum, a cytoplasm, a nucleus and three microtubular arms. The acrosomal vesicle is posteriorly penetrated by the perforatorial chamber and shows an inner acrosome zone, a thick ray zone and an electron dense outer acrosomal zone. The great importance of paguroid male reproductive apparatus morphology and ultrastructure for phylogenetic analysis is confirmed.