Abstract
An ultrastructural investigation of the porcellanid crabs, Aliaporcellana suluensis and Pisidia longicornis reveals that they possess small, spherical to ovoid, pedunculate spermatophores containing a few extremely elongate spermatozoa wound spirally inside the ampulla. In each species the ampulla is divided into two halves which join at a structurally complex, thickened lateral ridge. The spermatozoa of both species have small complex acrosomal vesicles with a perforate operculum and complex, concentric acrosome zonation. Several of these internal acrosome zones are autapomorphic characters for the spermatozoa of the Porcellanidae, when compared with previously studied anomuran spermatozoa. The elongate spermatozoa have a long tail-region composed of a central core of microtubules (autapomorphy) which has a collar of cytoplasm proximally and distally a nuclear sleeve. This central microtubular core splits distally to produce more than four external microtubular arms. The elongate, almost "flagellate", appearance of the spermatozoa of Aliaporcellana and Pisidia is unique for the investigated Decapoda.
