Scheltinga, D.M., Wilkinson, M.,
Jamieson, B.G.M. and
Oommen V.O. 2003. Ultrastructure of the mature spermatozoa of
caecilians (Amphibia: Gymnophiona). Journal of Morphology 258: 179-192.
The spermatozoa of
Gymnophiona show the
following autapomorphies: 1) penetration of the distal centriole by the
axial
fiber; 2) presence of an acrosomal baseplate; 3) presence of an
acrosome seat
(flattened apical end of nucleus); and 4) absence of juxta-axonemal
fibers. The
wide separation of the plasma membrane bounding the undulating membrane
is here
also considered to be apomorphic. Three plesiomorphic spermatozoal
characters
are recognized that are not seen in other Amphibia but occur in basal
amniotes:
1) presence of mitochondria with a delicate array of concentric cristae
(concentric cristae of salamander spermatozoa differ in lacking the
delicate
array); 2) presence of peripheral dense fibers associated with the
triplets of
the distal centriole; and 3) presence of a simple annulus (a highly
modified,
elongate annulus is present in salamander sperm). The presence of an
endo-nuclear canal containing a perforatorium is a plesiomorphic
feature of
caecilian spermatozoa that is shared with urodeles, some basal anurans,
sarcopterygian fish, and some amniotes. Spermatozoal synapomorphies are
identified for 1) the Uraeotyphlidae and Ichthyophiidae, and 2) the
Caeciliidae
and Typhlonectidae, suggesting that the members of each pair of
families are
more closely related to each other than to other caecilians. Although
caecilian
spermatozoa exhibit the clear amphibian synapomorphy of the unilateral
location
of the undulating membrane and its axial fiber, they have no apomorphic
characters that suggest a closer relationship to either the Urodela or
Anura.