141. Jamieson, B.G.M. and Koehler, L. 1994k.
The
ultrastructure of the spermatozoon of the Northern Water Snake, Nerodia
sipedon (Colubridae, Serpentes), with phylogenetic considerations. Canadian
Journal of Zoology 72, 1648-1652.
The ultrastructure of the spermatozoon of Nerodia
sipedon conforms closely to that of other described snake sperm: it
is
filiform; the acrosome vesicle is in the form of a hollow,
concentrically zoned
cone that basally overlies a subacrosomal cone which invests the
tapered anterior
end of the nucleus; the putative perforatorium is a slender rod
extending
anteriorly from the subacrosomal cone; the midpiece contains dense
bodies and
mitochondria; the axonemal fibrous sheath extends anteriorly into the
midpiece
(squamate autapomorphy); 9 peripheral dense fibres surround the distal
centriole and the axoneme in the midpiece, of which fibres adjacent to
3 and 8
are enlarged; and the endpiece lacks peripheral fibres and the fibrous
sheath.
The midpiece is very long (a synapomorphy of the Serpentes) and is
surrounded
by a multilaminar membrane (an autapomorphy).
In the squamates, only snakes, including N.
sipedon,
retain microtubules external to the plasma membrane of the mature
spermatozoon.
Helically arranged zigzag mitochondria are shared (probably
homoplasically)
with iguanid sperm. A poorly developed "stopperlike" putative
perforatorial base plate in N. sipedon, unknown in other
snakes, is
questionably homologous with that of gekkonids. An electron-lucent
space caps
the nuclear point, as in the snakes Boiga irregularis and Stegonotus
cucullatus and in some other squamate orders.