AN ULTRASTRUCTURAL INVESTIGATION OF HRABEIELLA PIZL-AND-CHALUPSKY, 1984 (ANNELIDA) .2. THE SPERMATOZOON

The mature spermatozoa of the terrestrial non-clitellate annelid Hrabe iella periglandulata Pizl & Chalupsky, 1984 s.l. were examined using l ight and electron microscopy. They are about 150 mu m long, filiform a nd extremely slender (maximum diameter, 450-475 nm). The acrosome is v ery elongate (about 25 mu m), tapering and conical. Its transverse sec tion is circular apically but shows an evident six-rayed symmetry in i ts basal region. The nucleus appears convex at both ends; apically, it extends laterally into the acrosome, and basally, it plugs into the c entriolar region. The nucleus is about 23 mu m long and has a rounded, tri-to pentalobed, slightly helical profile, The midpiece contains on e elongate, free (paraxonemal) mitochondrion, 27 accessory tubules, wh ich are slightly larger and more opaque than the axonemal microtubules ; and seven electron-dense, non-membrane-bounded rods distributed arou nd the axoneme. The flagellum tapers rapidly posteriorly. None of the observed similarities to the sperm (introsperm) of questids, protodril ids or other polychaetes seems to represent an immediate synapomorphy. None of the spermatozoal autapomorphies of the Euclitellata is shared by Hrabeiella.