CRASSATELLIDAE, Ferussac, 1822

Healy, John M., Mikkelsen, Paula M. & Bieler, Rüdiger, 2008, Sperm ultrastructure in Hemidonax pictus (Hemidonacidae, Bivalvia, Mollusca): comparison with other heterodonts, especially Cardiidae, Donacidae and Crassatelloidea, Zoological Journal of the Linnean Society 153 (2), pp. 325-347 : 333-335

( CRASSATELLIDAE ), CARDITA MURICATA ( CARDITIDAE )

Acrosomal complex

The acrosomal vesicle is elongate-conical (2.7 ± 0.1 Mm E. cumingii , N = 4; length 1.6 ± 0.1 Mm C. muricata , N = 4), sharply tapered anteriorly and almost completely invaginated ( Fig. 7A, B). The vesicle has a maximum diameter (at base) of approximately 0.35 Mm. Contents of the acrosomal vesicle are differentiated into a dense inner layer enveloped by markedly less dense material. ( Fig. 7B, C) The subacrosomal material is organized as a well-defined ·

axial rod that occupies not only the vesicle invagination but also a shallow apical invagination of the nucleus ( Fig. 7B).

Nucleus

The nucleus is rod-shaped (length 10.0 ± 0.2 Mm E. cumingii ; 7.4 ± 0.2 Mm C. muricata ) (N = 5), tapering (in each species) from a diameter of 1.0 ± 0.1 Mm (N = 6) near the base to 0.4 ± 0.05 Mm (N = 6) at the apex ( Fig. 7A, B, G, E). Aside from the apical invagination (accommodating part of the subacrosomal material), the nucleus exhibits a short invagination for the centriolar rootlet and slight concavities that contact the mitochondria ( Fig. 7E, G). Irregularly shaped electron-lucent lacunae are present throughout, though largest and most conspicuous posteriorly ( Fig. 7G).

Midpiece

The midpiece exhibits eight (occasionally seven or nine) mitochondria tightly packed around a dense rootlet plus distal centriole complex ( Fig. 7D–H). Profiles of the mitochondria are angular in transverse section, with the contacting surfaces of each being flattened. Although the distal centriole shows no modifications, the proximal one has been transformed into a portion of the rootlet attached anteriorly to a shallow indentation at the base of the nucleus and posteriorly to the distal centriole ( Fig. 7E–H). The distal centriole is anchored to the plasma membrane via a radial array of nine satellite fibres ( Fig. 7D), and is continuous with the doublets of the flagellar axoneme ( Fig. 7E). The entire midpiece region (in each species) has a length of approximately 0.65 ± 0.05 Mm (N = 8) and a maximum diameter of 1.7 ± 0.1 Mm (N = 8).

Flagellum

The flagellum consists of a 9 + 2 microtubular configuration axoneme, sheathed by the plasma membrane ( Fig. 7F). From light microscopic observations, flagellar length for both species is 47 ± 3.0 Mm (N = 10 per species).