Spermatozoa of the New Zealand
tuatara, Sphenodon punctatus punctatus (Gray), are
described from
light and electron microscopic observations and compared with
spermatozoa of other living 'reptiles' (Chelonia, Crocodilia,
Squamata), birds and mammals. Mature Sphenodon spermatozoa consist
of an
acrosomal complex (length 4mm),
elongate, helical nucleus (54-56 um), a relatively
short
midpiece (7-8um),
elongate principal piece (74-78um)
and short end piece
(2-4 um).
The acrosomal vesicle and underlying
subacrosomal material form a double, curved, conical sheath around
the nucleus
anteriorly. Two parallel, loosely helical, endonuclear canals
each
containing perforatorial material, extend posteriorly from the apex
of the
nucleus to at least 2.5 um
below the base of the acrosomal complex. Rings of
several spherical mitochondria are stacked around the elongate
distal
centriole to form the mouthpiece. Each mitochondrion has concentric
cristae
surrounding a dense central body. Proximal and distal centrioles,
although differing markedly in length, are similar in having triplets with an
open C tubule. Nine peripheral fibers are intimately associated with
the triplets of the distal centriole. A well developed annulus defines
the posterior extremity of the midpiece. The principal piece consists of
a 9+2 axoneme (accomplished anteriorly by nine peripheral fibers)
surrounded by a highly electron-dense fibrous sheath and the plasma
membrane. Absence of a penis in Sphenodon has not resulted in recognizable
modifications of the spermatozoon. Sphenodon shares many spermatozoal
features here interpreted as plesiomorphies with crocodiles and turtles,
particularly the latter group, but exhibits none of the advanced character
states (apomorphies) diagnostic of the Squamata. These data not only underscore the
primitive status of living tuatara (recently questioned in the
literature) but also militate against a close, sister-group
relationship between the Sphenodontida and Squamata.