Four species of Cystoisospora, C. canis, C. ohioensis, C. neorivolta and C. burrowsi are described from feces of dogs. Of these, the oocysts of C. canis are the largest and easily distinguished from the remaining three species. Oocysts of C. ohioensis, C. neorivolta and C. burrowsi are difficult to distinguish because of overlap in their sizes. However, based on endogenous developmental stages, C. ohioensis is distinct from C. neorivolta and C. burrowsi because its endogenous stages are confined to surface epithelium of intestine whereas endogenous stages of C. neorivolta and C. burrowsi are predominantly in the lamina propria. There are uncertainties regarding the endogenous stages of C. neorivolta and C. burrowsi and there is no way now to determine whether C. burrowsi and C. neorivolta are different parasites; therefore, these are referred as C. ohioensis-like organisms. Additionally, mode of division of asexual stages of coccidia of dogs is largely unknown and ultrastructural studies are lacking. In the present study, development of asexual and sexual stages of a C. ohioensis-like organism in a naturally infected dog is described by light microscopy and by transmission electron microscopy. Merozoites divided by endodyogeny/merogony. Meronts were crescent/merozoite-shaped and contained a maximum of eight nuclei. A distinctive feature of merozoites was the presence of many PAS-positive amylopectin granules that were absent or rare in immature microgamonts making it possible to distinguish them.

A new species of the sabellid genus Pseudobranchiomma is described from 50 cm depth in dock fouling from the southern Gulf of California. Pseudobranchiomma schizogenica sp. nov., belongs to a group of six species characterized by having radiolar serrations extending for most of the radiolar length. The new species is characterized by the presence of a unique set of features related to the covering of the peristomium by lateral collar margins, the shape of the first ventral shield, the size of interramal eyespots, and the width of the hood of thoracic and abdominal spinelike chaetae. Information about live and post-fixed colour, glandular pattern and reproduction is also provided. The new species described here is compared with all species in the former group. The presence of paired patches of cilia without heads (kinocilia-type) on ventral lappets and ventral shields of the collar, thorax and abdomen is documented for the first time in the genus Pseudobranchiomma. Dense aggregations of Pseudobranchiomma schizogenica sp. nov., on docks from the southern Gulf of California are predominantly a result of asexual reproduction taking place during summer, when 82% of the population reproduces by architomy.

In the rodent malarial parasite Plasmodium berghei sexual parasites are produced in a single major wave with maximal numbers between day 7 and day 16. Irrespective of their time of appearance during infection these sexual parasites are equally fertile in vitro. In contrast, in vivo infectivity to the mosquito is maximal at day 3–5 when gametocyte numbers are only 9% of the peak levels seen between days 7 and 16. Up to 96% of natural potential infectivity of gametocytes for the mosquito is therefore suppressed. The suppression is humoral, reversible and correlates with the appearance of an effective host response to the initial rapid increase in asexual parasitaemia. These data are consistent with published evidence which indicates that a reduction in parasitaemia may cause an increase in infectivity of gametocytes to the mosquito vector. Therefore the impact of strategies aiming to control asexual parasites is re-examined. Inefficient strategies might be predicted to increase and not suppress malaria transmission.