Jamieson, B.G.M., Afzelius, B.A. and
1985b. Ultrastructure of the acentriolar, aflagellate spermatozoa and
the eggs of Histriobdella homari and Stratiodrilus
novaehollandiae (Histriobdellidae, Polychaeta). Journal of
Submicroscopic Cytology 17, 363-380.
features of the filiform histriobdellid spermatozoon and late spermatid
are a very long, complex acrosome, with preformed perforatorium; an
elongate nucleus, a long anterior portion of which forms a narrow shaft
surrounded by regularly cristate mitochondria (four in Stratiodrilus,
eight or nine in Histriobdella); anterior invagination of the
tip of the nucleus to form a beaker-shaped pedestal, fenestrated in Histriobdella,
and subdivided into four prongs in Stratiodrilus or eight in Histriobdella,
supporting the base of the acrosome; and posterior narrowing of the
wide elongate hind portion of the nucleus to form the posterior end of
the spermatozoon. The anterior region of the acrosome is composed of
spiral laminae (4 in Stratiodrilus, 6 in Histriobdella).
A flagellum is totally absent at all stages of development and
centrioles are absent from the mature spermatozoon of either species
though transiently present in the spermatid (Stratiodrilus).
The egg envelope consists of the oolemma overlain by a thick vitelline
envelope which is cuticle-like but lacks true epivitelline projections.
Outside this in Stratiodrilus there is a thick reticular layer.
Euspermatozoa have three functions: putative fertilization, and,
on degeneration, contribution to the substance of the egg and formation
of the reticular layer, the latter from the mitochondrial cristae.