101. Jamieson, B.G.M. 1989g. Complex spermatozoon of the
live-bearing
half-beak, Hemirhamphodon pogonognathus (Bleeker):
ultrastructural
description (Euteleostei, Atherinomorpha, Beloniformes).
Gamete Research
24, 247-259.
The spermatozoon of H. pogonognathus shows modifications
that are frequent though not obligate in internally fertilizing sperm,
notably elongation of the nucelus and extension of the mitochondria of
the midpiece as an elongate sheath around the proximal region of the
axoneme.
These similarities to poecilid and jenynsid sperm are considered
homoplasic. As in the mature sperm of all but one investigated
teleost,
an acrosome is absent. The elongate, blade-shaped, electron-dense
nucleus has a mean length of 3.2 um; its
basal implantation fossa, less than one-tenth of the length of the
nucleus,
houses the anterior half of the distal and only centriole (of triplet
construction
with satellite rays), a centriolar plug, and a mass connecting the
centriole
of the wall of the fossa. A unilateral putative centriole adjunct
is present. The anterior region of the axoneme is surrounded by a
mitochondrial
sleeve, and internal to this, separated by a cisterna, by a
submitochondrial
sleeve. The mitochondrial sleeve units posteriorly with the
submitochondrial
sleeve. Between the submitochondrial sleeve and the axoneme is a space,
the cytoplasmic canal, that is open to the exterior posteriorly.
The discrete, cristate mitochondria, in their sleeve, are unique in
investigated
atherinomorph sperm in being bilateral, grouped on only two opposing
sides
of the axoneme, with an arc-shaped "intermitochondrial link" between.
The
9 + 2 flagellum is unique for the Animalia in having 23 radial
subplasmalemmal
rods, repeated longitudinally (periodicity 0.025 um)
in a quasicrystalline array. Internal fertilization is deduced to have
arisen in the Exocoetoidei independently of that in the
Cyprinidontiformes.
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