ABSTRACT
The gummy shark, Mustelus antarcticus, is an example of an animal with minimal histotrophy. Storrie (2004) studied histological and ultrastructural changes in the uterus of females throughout gestation. The gummy shark has several characteristics associated with placental sharks. Foremost is the development of uterine compartments. The uterus does not possess villi as is seen in some of the animals with incipient histotrophy but surface area available to each embryo is provided by individual uterine compartments. Another feature shared with placental
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species is a persistent tertiary egg envelope that is present throughout gestation. The oviducal gland is virtually identical both at the gross, light
microscopic and ultrastructural levels to that in the placental, M. canis (Hamlett eta/. 2002). The average total dry weight of multiple ova samples was 2.267 g. Average embryo total dry weight at approximately midgestation was 8.55 g representing an increase in dry mass of 377.21 '1\,. Term samples weighed an average of 17.775 g or a 784.19% increase over the egg. ln early to mid-gestation the uterine epithelium is stratified and
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416 Reproductive Biology and Phylogeny of Chondrichthyes
is dominated by high mucous secretory activity (Figs 13.7 A, B). By near term the uterine mucosa has undergone a striking morphological mo,d.ification. The epithelium thins to simple squamous and mucous seq·etion dissipates and disappears. Vessels proliferate, dilate (Figs 13.7C, D) alild are in intimate contact with the basal lamina of the epithelium (Fig .. ll7C). A prominent feature is the presence of extensively dilated spaces (Fig. 13.70). We conclude that abundant mucous secretion augments yolk stores in early and mid-gestation and water and mineral trapsfer primarily occur in later gestation. This accounts for the substantial dry weight gain over species like Pristiophorus.
