Spermatozoan ultrastructure in the trigonioid bivalveNeotrigonia margaritacea Lamarck (Mollusca): Comparison with other bivalves, especially Trigonioida and Unionoida

Abstract

Spermatozoa of the trigonioid bivalve Neotrigonia margaritacea (Lamarck) (Trigoniidae, Trigonioida) are examined ultrastructurally. A cluster of discoidal, proacrosomal vesicles (between 9 to 15 in number) constitutes the acrosomal complex at the nuclear apex. The nucleus is short {2.4-2.6 ~m long, maximum diameter 2.2 ~tm), blunt-conical in shape, and exhibits irregular lacunae within its contents. Five or sometimes four round mitochondria are impressed into shallow depressions in the base of the nucleus as is a discrete centriolar fossa. The mitochondria surround two orthogonally arranged centrioles to form, collectively, the midpiece region. The distal centriole, anchored by nine satellite fibres to the plasma membrane, acts as a basal body to the sperm flagellum. The presence of numerous proacrosomal vesicles instead of a single, conical acrosomal vesicle sets Neotrigonia (and the Trigonioida) apart from other bivalves, with the exception of the Unionoida which are also known to exhibit this multivesicular condition. Spermatozoa of N. margaritacea are very similar to those of the related species Neotrigonia bednalli (Verco) with the exception that the proacrosomal vesicles of N. margalqtacea are noticeably larger than those of N. bednalli.

Sperm ultrastructure in Hemidonax pictus (Hemidonacidae, Bivalvia, Mollusca): comparison with other heterodonts, especially Cardiidae, Donacidae and Crassatelloidea

“…A number of species of Cardiidae ( sensu Schneider, 1992, 1995; now inclusive of Tridacnidae as subfamily Tridacninae) have been examined for sperm ultrastructure (Popham, 1979; Sousa & Azevedo, 1988; Healy, 1995b; Sousa et al ., 1998; Keys & Healy, 1999, 2000; Drozdov et al ., 2001; present study) and even though many genera and even some subfamilies await investigation, enough is known to provide a meaningful comparison with Hemidonax pictus (see Figs 8, 9). Sperm morphology in the Cardiidae varies widely between taxa, to such an extent in fact that no distinctive, family‐defining characters are yet apparent.…”

“…Comparative studies of bivalve sperm ultrastructure have shed new light onto higher relationships within the class (Popham, 1979; Healy, 1996a) and the systematics or phylogeny of several important taxa (e.g. Mytiloidea –Hodgson & Bernard, 1986; Kafanov & Drozdov, 1998; Palaeoheterodonta –Healy, 1989, 1996a, b; Pteriomorphia –Healy, Keys & Daddow, 2000; Crassatelloidea –Healy, 1995a, b; Galeommatoidea –Jespersen, Lützen & Morton, 2002; Veneroidea –Gharagozlou‐Van Ginneken & Pochon‐Masson, 1971; Healy, 1995b; Healy, Mikkelsen & Bieler, 2006). With this in mind, we have carried out a sperm ultrastructural study of a representative species of Hemidonax [using the type species H. pictus (Tryon, 1870)] in order to clarify the relationships of the genus to other Veneroida.…”

Umbonal musculature and relationships of the Late Triassic filibranch unionoid bivalves

“…The close affinity of the marine Neotrigonia and freshwater unionoids is generally accepted (Waller, 1998; Graf & Ó Foighil, 2000; Hoeh, Bogan & Heard, 2001; Giribet & Wheeler, 2002). This is supported by: the hinge structure and shell musculature (Newell & Boyd, 1975); the ultrastructure of sperm, with unique, multiple, unfused proacrosomal vesicles in mature spermatozoa (Healy, 1996); and molecular phylogenetic evidence (Hoeh et al ., 1998). Among plesiomorphic aspects of the trigonioids, the byssal organ in juveniles (Gould, 1969), their aragonitic nacreous shell, free mantle margins, and striated teeth of the hinge were inherited by the unionoids (Graf & Cummings, 2006).…”

Ultrastructural aspects of spermatogenesis in Calyptogena pacifica Dall 1891 (Vesicomyidae; Bivalvia)

“…The midpiece of spermatozoa in C. pacifica contains four or rarely five mitochondria. The varying number of mitochondria is a frequently occurring phenomenon in bivalves (e.g., Gladyshev & Drozdov, 2002;Healy, 1996;Introíni et al, 2013;Keys & Healy, 1999) and in Venerida species (supplementary online material, Table S1). Four or five mitochondria were found in Coecella chinensis (Kim & Lee, 2019), Pitar rudis (Erkan & Sousa, 2002), Paphia philippiana (as P. exarata) (Chen et al, 2006), Arctica islandica, and N. sublaevigatum (Healy et al, 2020).…”