Abstract
Ph.D. (Zoology)
D. ranarum was sampled from the Limpopo River System. It was studied
morphologically by means of light microscopy of whole mounts and
scanning electron microscopy. The histology of this organism was also
studied. As this parasite was described in 1891, a comprehensive
description of the species was done by means of scanning electron
microscopy. Graphic reconstructions of the genital systems were done
in order to verify and elucidate its morphology. Various areas of said
systems were histologically characterised and deductions made concerning
the functions of the various cell-types and structures. Two
glands, i.e. a digestive- and a spermatophoric gland were identified
and described from the carapace of the male. Eggs sampled in the
laboratory were studied with reference to hatching times and larvae
were described morphologically. It was found from the aforegoing that
larvae are parasitic directly after hatching. A histological study of
host-damage by the parasite was done and it was found that infestation
by ranarum causes loss of epithelial tissue, oedema and haemorrhage.
The shape of the lesions were correlated with the shape and
orientation of the adhesive appendages of the parasite. As significant
confusion exists concerning the terminology used in the study of this
group of animals, a list of such terms was compiled in order to
delineate this. The role of environmental temperature as a factor
influencing the limited geographical distribution of D. ranarum in
Africa is discussed and the theory of continental drift is proposed as
a possible explanation for the global distribution of this group.