Some aspects of the reproductive biology of Fusitriton oregonensis (Redfield) (Gastropoda, Prosobranchia)
Date
1976
Authors
Williams, Daphne Eiri
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Abstract
Little is known of t he reproductive biology of the prosobranch Fusitriton oregonensis (Redfield). Therefore this thesis describes the morphology and histology of the male and female reproductive tracts, the spermatogenesis of all types of sperm and their structure.
Both the male and female reproductive systems are in an advanced mesogastropod state, approaching the neogastropod condition. Primitive features of the male system are an open prostate gland and an open sperm groove extending along the phallus. The least advanced feature of the female system is the seminal receptacle which is merely a dilation of the distal portion of the oviduct.
Three types of sperm develop in the testes of F. oregonensis continually throughout the year. Maximum production however, occurs during February, March and April. Two sperm lines develop, (1) the eupyrene or fertilizing sperm and (2) the apyrene anucleate sperm, of which there are two types, the carrier and the lancet. Development of eupyrene sperm is typical but complex; one spermatogonium produces four haploid sperm after two meiotic divisions. In contrast, development of apyrene is atypical and direct; one spermatogonium produces one sperm. The nucleus of the spermatogonium fragments and degenerates within the cell. Cellular differentiation is not complex.
The most numerous and active of all three types are the eupyrene sperm. They are long and filamentous, similar to other gastropod sperm. The acrosome is conical and hollow. A rod extends through the subacrosomal space which also contains a subacrosomal granule. Posterior to the acrosome is a modified centriole from which extends an axoneme of the standard 9+2 pattern. The nucleus is cylindrical, encircling the axoneme distal to the acrosome. Distal to the nucleus is a mitochondrial spiral also encircling the axoneme and further distal is the glycogen region. Grouped glycogen rosettes having a characteristic pattern extend to the end of the tail piece where the axoneme emerges free for a short distance.
The slow-moving carrier apyrene sperm is short and fusiform. Through its centre runs a core of axonemes of standard configuration, each of which extends from an anterior modified centriole. Encircling the core are tightly packed large droplets containing acid mucopolysaccharide complexed with protein. Dispersed amongst these are glycogen rosettes and a few mitochondria. Fifty or more eupyrene sperm attach to one carrier sperm forming a spermatozeugma. Carrier sperm are probably a nutrient source for eupyrene sperm. There may be other less obvious functions for the spermatozeugrnata.
Lancet apyrene sperm are long and so named because of their shape. They are less active than the carrier sperm and eupyrene sperm do not attach to them. Several standard axonemes arise from apically placed modified centrioles and extend beneath the plasmalemma distally to the end of the sperm; single microtubules lie in a similar position between the axonemes. Disposed anteriorly in the cytoplasm are mitochondria and numerous small droplets containing acid mucopolysaccharides complexed with protein. Posterior are several large mucus - containing droplets. Scattered throughout the cytoplasm are glycogen rosettes. The roles of the lancet sperm are less obvious than those of the carrier.
After copulation, the three types of sperm are stored for a short time in the female copulatory bursa. Most eupyrene sperm move to the seminal receptacle for some time prior to fertilization. Apyrene sperm remain in the viscous fluid in the copulatory bursa. Lancet sperm appear to begin degeneration and entrap any other sperm remaining in the bursa, producing plasmodial-like formations. The significance of this is uncertain.