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Onychophoran‐euclitellate relationships: evidence from spermatozoa l ultrastructure
Author(s) -
JAMIESON BARRIE G. M.
Publication year - 1986
Publication title -
zoologica scripta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.204
H-Index - 64
eISSN - 1463-6409
pISSN - 0300-3256
DOI - 10.1111/j.1463-6409.1986.tb00217.x
Subject(s) - axoneme , biology , autapomorphy , acrosome , anatomy , centriole , sperm , ultrastructure , annulus (botany) , clitellata , flagellum , microbiology and biotechnology , phylogenetics , paleontology , genetics , botany , semen , bacteria , gene
Onychophoran sperm share striking apomorphies with sperm of oligcchaetes: the elongate, cylindrical, strongly condensed nucleus with (enchytraeid oligochaetes only) spiral keel(s); interpolation of mitochondria, which are spiral as in some microdriles, between nucleus and axoneme (autapomorphy); presence of postmitochondrial annulus; occurrence of a basal cylinder at the anterior end of the two central singlets (autapomorphy). Onychophoran sperm differ notably from oligochaete sperm: in possessing periacrosomal material; in the helical coiling, reduction, or absence of the acrosome vesicle (though acrosomal coiling occurs in leeches); in the conical subacrosomal structure contrasting with the characteristic acrosome tube of euclitellates; in the absence of a perforatorium (though these two features could be consequent on the reduction of the acrosome); in lacking a distinct padlike thickening of the anterior nuclear envelope; in possessing (external to the mutual 9 + 2 axoneme) 9 peripheral singlets and a subplasmalemmal microtubular manchette (also present in questid annelids); and in the scattered, rather than regularly arranged, peripheral glycogen of the axoneme; they also lack two additional fibres which give the characteristic tetragon of the oligochaete axoneme; and, although the centriolar triplets are disrupted, having a more complete distal centriole than in euclitellates. The remarkable similarities to euclitellate sperm, coupled with embryological similarities between Onychophora and Euclitellata, suggest that the onychophoran‐euclitellate assemblage is a monophyletic group and the sister‐group of the myriapod‐hexapod assemblage. Wider phylogenetic implications of these findings are discussed.