African Zoology - Volume 34, Issue 4, October 1999

Sitala jenynsi snails from the University and Wazo populations of Dar es Salaam, Tanzania, were released on grass, and on forest terrain, in both regions during the dry (February, March) and the rainy seasons (April). Snail dispersion was assessed as weekly quadratic means and as the overall Diffusion Coefficient 0.423 m�/week. The coefficient was enhanced by grassy habitats, continuous vegetation cover, absence of edible plants and rainy weather: conversely, dispersion was retarded by shrubs, vegetation discontinuities, presence of edible plants and dry weather. There were differences in the rate of dispersion between populations. snails from the University Campus being faster. In each release a broadly unidirectional dispersion was recorded. The populations in question, seasons and the direction of origin of the snails seemed immaterial to directionality of dispersion. The dispersion rates of Sitala jenynsi exceeded those of the helicids Cepaea nemoralis and Theba pisana and of the partulid Parlula taeniata. While observed dispersion rates of S. jenynsi may warrant the mixing of individuals in a population. they seem insufficient to facilitate appreciable migration of snails between neighboring populations.

The habitats and patterns of vertical migration of the shell banding morphs of the snail Sitala jenynsi (Pfeiffer) were studied in Dar es Salaam and Wazo regions of central coastal Tanzania Both dimorphic and trimorphic populations were arboreal throughout the year. The snails occurred randomly within mid-heights 180 to 360 cm. without apparent morph differences in micro-distribution. The pattern of circadial vertical distribution consisted of upward migrations during mornings and downward shifts during late evenings. These oscillations regressed negatively on relative humidity (RH), a unit advance in RH representing an eight-fold descent of snails on daytime height. Variations in RH accounted for much of the total variance in the mean vertical distance. During high RH, however, temperature and mating behaviour probably exerted major influences on snail micro-distribution. The effects of arboreality on snail survival and initiation of differentiating subpopulations are proposed.

The Cape clawless otter (Aonyx capensis) is one of the few species of mammals that occur in both freshwater and marine habitats, and it therefore must be able to tolerate the high rates of water flux typical of aquatic animals as well as the desiccating effects of seawater. The clawless otter has paired, discrete multirenculate kidneys (total mass = 172 g) comprised of both unipapillary and bipapillary renculi weighing an average of 2.6 and 3.2 g, respectively. The average thickness of the cortex is 2.3 mm, and thicknesses of the outer and inner medulla are 2.4 and 6.4 mm. respectively. These measurements and the overall structure of the kidney of the Cape clawless otter are intermediate between those of freshwater and marine mammals.

Reports the results of an investigation into the metabolic rate of individuals and clusters of Miniopterus schreibersii, conducted to assess their thermoregulatory capabilities, the effect of clustering on their thermoregulation, and the implications of roost microclimate for metabolism and hibernation in the species. Illustrates with graphs.

Three species of the rocky-shore inhabiting mite genus Amhyadesia Fain and Ganning 1979 (Acari: Astigmata: Hyadesiidae) were present In collections made across the extent of the southern African sub-continent, from Elandsbaai on the west coast to Inhambane (Mozambique) on the east coast. Two are new species, A austafricana spec. nov. and A elizabethensis spec. nov., and are descriptionbed herein. The third species, A heterophallus, collected from the east coast only, is widely-distributed throughout the Indo-Pacific region.

Spatial aggregations of organisms are common in nature. Aggregations have often been thought to play important roles in mate-finding, predator avoidance, reduction of water loss, or the acquisition of food and other resources, yet few empirical studies have been done on the processes that lead to aggregation We studied aggregations of the giant isopod Tylos granulatus, which lives as a scavenger in the intertidal zone of sandy beaches on the west coast of South Africa. Individuals emerge with the receding tide leaving exit holes, then forage for about two hours before returning to the vicinity of the high-water mark where they aggregate to bury themselves, leaving behind cone-shaped mounds. Our observations showed there was no correlation between aggregations and the availability of food, and that manipulating the position offood had no effect on the aggregations. Reproduction, which is seasonal and synchronous. also seems unlikely to explain the year-round aggregations. Experiments showed T. granulatus preferentially burrows in existing holes or mounds rather than creating new ones. The advantages of this are analysed in terms of energy conservation, and as a means of reducing risks of exposure to predators or being swept away by the Incoming tide. Whatever the benefit, the preferential use of existing holes can incidentally lead to aggregation, which may not itself have any adaptive function.

In-situ observations and photographs of an unusual and spectacular red and white striped, mobile anemone, which appears to feed on gorgonians on sublittoral habitats on the south and east coasts of South Africa, prompted a closer examination of two preserved specimens. The specimens are identical with Condylactis natalensis Carlgren. 1938. which was descriptionbed from a single preserved specimen and has not since been reported. The redescriptionption of the species indicates that a new genus, Korsaranthus, is required to accommodate it within the family Actiniidae. Most significant characteristics of K. natalensis are the lack of p-mastigophares in its cnidome and the folded, distal-most part of its actinopharynx, features that compare with members of order Ptychodactiaria, which are predators of octocorals, too.

Reports the results of a study dealing with the fine anatomy of the prostate of the Subantarctic fur seal at Gough Island, conducted to determine if there are any changes in the micro-anatomy of the male seal prostate over the study period, which might correlate with the reproductive state, and how the size and histology of the prostate change with increasing age.