AN ULTRASTRUCTURAL STUDY OF SPERMATOZOA OF HELIX ASPERSA AND HELIX POMATIA (GASTROPODA, PULMONATA)

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Abstract
Spermatozoa of the pulmonates Helix aspersa Müller and H. pomatia Linnaeus are examined in detail using transmission electron microscopy (TEM). Important features such as the acrosome, perinuclear sheath, nucleus and terminal region of the midpiece are described for the first time. Also presented are the first ultrastructural observations on spermatozoa from spermatophores in any pulmonate gastropod (H. aspersa). No morphological differences could be found between sperm taken from spermatophores and those within the hermaphrodite duct in H. aspersa. Spermatozoa of H. aspersa and H. pomatia snow all the characteristics of euthyneuran spermatozoa, namely: a helically-keeled nucleus; distinctive arrangement of acrosomal components (apical vesicle, acrosomal pedestal), and extremely elongate midpiece (axoneme and glycogen helix enclosed by matrix and paracrystalline layers). The sperm nucleus of both species is short, and the midpiece also forms the terminal portion of the spermatozoon (glycogen piece absent). The extraordinary positioning of the acrosome in H. aspersa—reflected backwards from the nuclear apex—is not observed in H. pomatia, though a perinuclear sheath (possibly another acrosomal component) is present in sperm of both species. Helix spermatozoa are compared with other euthyneuran sperm and briefly discussed from the systematic viewpoint.