Two sperm types in the spermatozeugmata of Tubifex tubifex (annelida, oligochaeta)

The spermatozeugmata (sperm bundles lacking a distinct wall) from the spermathecae of Tubifex tubifex are composed of two different zones: an internal axial cylinder containing conventional spermatozoa and an external cortex composed of modified spermatozoa, tightly packed together. The conventional spermatozoa conform to the classical clitellate scheme: very long and thin with a complex acrosome, a filiform nucleus, small mitochondria, and a flagellum with Y links and β glycogen granules as accessory structures. The modified spermatozoa show “empty” acrosomes, degenerating nuclei, and tails which contain γ glycogen granules. The tails are helically wound around the spermatozeugma and are connected to each other by junctional complexes. The tips of the cortical tails are free and move with a metachronal wave. The presence of two sperm types in tubificids is discussed and a protective function for the modified cortical spermatozoa is proposed.