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The ecology of an exploited population of the commercially important molluscan species, Pachymelania byronensis (Wood, 1828) was studied (January-December, 2018) in the lower Cross River, Nigeria, using density [number per hectare (N. ha-1)] as measure of stock abundance. The results revealed that the river supports a considerable stock of the gastropod (density range: Drange = 508000 – 12510000 N. ha-1; mean: Dmean = 4849833N.ha-1). The density decreased by 12002N. ha-1 (i.e. 10001667N. ha-1 mo-1) between January and December, a reflection of the increasing human exploitation as the year progressed. However, the monthly density changes scored low stochasticity (randomness), a product of the resilience of the population to human exploitation. The monthly densities were significantly correlated with river limnological parameters, including surface temperature, discharge, water level, transparency, dissolved oxygen concentration and hydrogen ion concentration. The coefficients of determination showed the decreasing order of theimportance of these parameters as: transparency (67.8%), water level (57.0%), surface temperature (43.5%), pH (40.5%), dissolved oxygen concentration (36.1%) and discharge (34.3%). The monthly values of biotic potential (rmax) were used to show trends in the population dynamics. Major density decreases were noted in February (rmax = -5.456) and December (rmax = -2.931) whereas notable density increases were recorded in January (rmax = + 3.204) and November (rmax = + 3.052). The value of the annual mean biotic potential (mean: rmax(mean) = -0.191) portrayed the general effect of heavy human exploitation on the mollusc. Hence, the gastropod total mortality rate was high (Z = -3.204 yr-1) The river carrying capacity of the gastropod was estimated at 12510000N ha-1. The monthly biotic potential correlated significantly with habitat temperature and dissolved oxygen concentration, two important life support parameters. Keywords: Pachymelania byronensis; density; biotic potential; exploitation; Cross River; Nigeria.

Levels of trace metals (Cd, Cr, Cu, Pb and Zn) were quantified in water, sediment and winkles (Pachymelania bryonensis and Pachymelania fusca mutans) in Akani Obio Uruan River, Nigeria during wet and dry seasons using standard procedures. Results revealed that mean levels (mg/l) of the metals in water ranged from 0.016 for Cr to 0.087 for Cd in wet season and 0.010 for Cu to 0.082 for Zn in dry season. In sediment, the metals levels (mg/kg) ranged from 0.002 for Pb to 0.161 for Zn in wet season and 0.001 for Pb to 0.438 for Cu in dry season. In winkles, the metals levels (mg/kg) ranged from 0.002 for Pb to 0.069 for Cd and for Cu in the wet season, and 0.001 for Pb to 0.058 for Cd and for Cu in the dry season. Estimated human health risk from each metal contamination due to consumption of the water, dermal absorption through swimming and consumption of winkles gave each of hazard quotient (HQ) and hazard index (HI) values of less than one (< 1), indicating no risk since the levels of contamination in each case are not likely to cause any adverse health effects in humans.

An assemblage of gastropods from the Thanetian of the Kolosh Formation from the Zakho region in northern Iraq is documented for the first time. The ten species represent the families Campanilidae Douville 1904, Potamididae H. & A. Adams 1854, Batillariidae Thiele 1929, Thiaridae Gill 1871, Pachychilidae Fischer & Crosse 1892, Cerithiidae Fleming 1822 and Pseudolividae de Gregorio 1880, suggesting a littoral to shallow sublittoral depositional environment. Six of the species are new and five are formally described as new species. At least seven species are also known from the Thanetian and/or Early Ypresian of the Ankara region in Turkey. Only a single species occurs also in the Paleocene of the Paris Basin. No relation to Paleocene and Eocene faunas of Pakistan and India is detectable. This points to a considerably bioprovincialism along the northern coast of the Tethys. Consequently we suppose the existence of an Anatolian Province in the Thanetian/Ypresian Mediterranean Region of the Tethys Realm, represented by rather homogeneous mollusc faunas from western Turkey and northern Iraq. Campanile zakhoense nov. sp., Pyrazopsis hexagonpyramidalis nov. sp., Pachymelania islamogluae nov. sp., “Faunus” dominicii nov. sp. and Pseudoaluco mesopotamicus nov. sp. are introduced as new species. Varicipotamides Pacaud & Harzhauser nov. nom. is proposed as the replacement name for Exechestoma Cossmann (1889) non Brandt (1837).

The effect of varying concentrations of petroleum drilling mud additive (Chromelignosulphonate) on three species of periwinkle and their microbial populations was studied. The periwinkles, Pachymelania byronensis. Pachymelania fusca and Tympanotonus fuscatus, were monitored in aquaria with different concentrations of the mud additive – 100, 500, 1000, 1500, 2000 mg/1 for 2 weeks. The bacterial isolates obtained from the molluscs were Micrococcus luteus, Micrococcus varians, Bacillus cereus, Bacillus brevis, Staphylococcus aureus, Corynebactrium, ovis, Vibrio anquillarium and Aeromonas hydrophila while fungal species were Aspergillus niger, Penicillum sp., Fusarium moniliforme, Aspergillus achraceus and Mucor sp. There was a decrease in the microbial biomass with increase in concentration of the mud additive. The mortality rate of the different species increased also with increase in concentration of the mud additive. There was high correlation (r= 0.56) between chromium ingestion and the mortality rate of the periwinkles.