This paper describes the morphology of Cucullanus pinnai pinnai parasitizing Pimelodus maculatus in the Guandu River, Brazil, based on differential interference contrast (DIC) microscopy and scanning electron microscopy (SEM), providing new morphological data about this species of parasite. Nematodes were collected between May and October 2012 from specimens of Pimelodus maculatus in the Guandu River (22°48'2"S, 43°37'35"W), in the state of Rio de Janeiro, Brazil. Some characteristics of specimens of Cucullanus in this study fall within the range of morphological variations of previously studied C. pinnai pinnai. Most of the specimens studied here had excretory pore and deirids located at the posterior end of the oesophagus, a feature not recorded in previous studies of this species. In addition, the size of the gubernaculum was larger than the other specimens previously studied. The SEM and DIC analyses of C. pinnai revealed several morphological details of the cephalic region and the tail papillae. With regard to the polymorphism of C. pinnai, morphological and genetic studies of this cucullanid nematode are needed, involving large numbers of host species and a wide geographical distribution.

The presence of cyathostomin larvae is directly associated to climatic conditions of each region. This study aimed to evaluate the ecology of infective larvae on Brachiaria humidicola during the dry and rainy seasons from October 2007 to September 2008 in a tropical region, Rio de Janeiro state, southeastern Brazil. Stools were collected from the rectum of horses naturally infected with cyathostomins at the beginning of the rainy season (October to March) and dry season (April to September). They were divided into four samples of 500 g and deposited on a grass patch of B. humidicola. Seven days later and every 15 days thereafter samples of feces and grass were collected and processed by the Baermann technique. The mean number of larvae recovered from the grass varied according to the season, with greater recovery of larvae during the peak of the dry season (14,700 L 3 .kg -1 DM). There was a statistically significant difference between L 3 recovered from feces and grass, but not between L 3 recovered from the grass base and apex. These results show that the region's climate favors the development and survival of infective cyathostomin larvae throughout the year, with a greater number of larvae during the dry season.Keywords: Infective larvae, wet and dry seasons, Brachiaria humidicola, cyathostomin. ResumoA disponibilidade de larvas de ciatostomíneos está diretamente relacionada com as condições climáticas de cada região. Para avaliar o comportamento das larvas infectantes nos períodos seco e chuvoso em gramínea Brachiaria humidicola, realizou-se um estudo, no período de outubro/2007 a setembro/2008, na região da Baixada Fluminense, RJ, de clima tropical. Amostras de fezes foram coletadas diretamente do reto de equinos naturalmente infectados por ciatostomíneos, no início do período chuvoso (outubro a março) e seco (abril a setembro), divididas em quatro amostras de 500 g e depositadas em um canteiro formado por gramínea B. humidicola. Sete dias após o depósito e, posteriormente, a cada 15 dias, amostras de fezes e gramíneas, foram coletadas às 8 horas e processadas pela técnica de Baermann. O número médio de larvas recuperadas da gramínea variou conforme os períodos, ocorrendo maior recuperação no ápice do período seco (14.700 L 3 .kg -1 . MS). Diferença significativa ocorreu entre a contagem de L 3 recuperadas das fezes e gramínea e não significativa entre as de L 3 recuperadas nas duas alturas da gramínea. Concluiu-se que as condições climáticas da região favorecem o desenvolvimento e a sobrevivência de larvas infectantes de ciatostomíneos durante todo o ano, com maior disponibilidade no período seco.Palavras-chave: Larvas infectantes, períodos chuvoso e seco, Brachiaria humidicola, ciatostomíneos.