Bacciger bacciger (Trematoda, Fellodistomidae) infection in commercial clams Donax trunculus (Bivalvia, Donacidae) from the sandy beaches of the Western Mediterranean

Sporocysts of the Fellodistomidae trematode Bacciger bacciger were embedded in gonadal tissue of the bivalve Donax trunculus from the Mediterranean coast of Spain. The overall prevalence of infection was 8.4 %, increasing with host size to 23 % in D, trunculus from 35 to 36 mm in shell length. Individuals <19 mm long were not infected. No clear seasonality was recognized in prevalence of infection. The proportion of infected individuals of both sexes was similar (6.56% in males and 8.04 % in females), although the highest prevalence was in clams of unknown sex (13.47 %). The proportion of infected clams reduced to virtual castrates of unknown sex reached 28%. The tegument of the sporocyst and shed cercariae was studied by light and electron microscopy. Scanning electron microscopy revealed a smooth surface on the sporocyst tegument, the area of which was greater due to the presence of circumferential infolds and numerous pits. A birth pore on one side of the sporocyst, uniciliate sensory organs and cup-shaped sensory-like structures were present on the tegument. The cercarial body had spines and uniciliate sensory organs. The ventral sucker of the cercariae had 2 rings of uniciliate sensory organs and tegumental spines.