Morphological and Histochemical Characterization of Gill Filaments of the Brazilian Endemic Bivalve Diplodon expansus (Küster, 1856) (Mollusca, Bivalvia, Hyriidae)

Abstract

This study presents the morphological description and histochemical characterization of gill filaments of the Brazilian endemic bivalve Diplodon expansus, aiming to broaden the morphological knowledge of this species and establish the structure of the gills that will serve as control in histopathological studies applied to biomonitoring. The gill filaments are divided into three zones: frontal, intermediate, and abfrontal. In the center of the filament, haemocytes circulate through the haemolymph vessel, which is internally lined by endothelium. The frontal surface of the filament is covered with cilia, the lateral surface exhibits aquifer ducts, and the abfrontal surface presents ciliated and nonciliated cells. The epithelium of the filaments is composed of ciliated cells, nonciliated absorptive cells, and mucocytes. The support of the filaments is made by two specialized structures called skeletal rod and skeletal loop. Based on the obtained information, the gill filaments of the studied species present some peculiar characteristics that are not yet reported in detail in the literature such as the simultaneous presence of skeletal rod and skeletal loop. On the other hand, the general constitution of the filament is similar to that described for both marine and limnic bivalves and seems to be suitable for ecotoxicological studies.

Histological Responses of The Freshwater Clam, Caelatura nilotica (Cailliaud, 1827) to Different Environmental Degrees Of Mixed Pollution

“…Some of the present clams exhibited skeletal tissue instead of the basal lamina in the more polluted site. This result was pointed out by Nogarol et al (2012) who described the presence of this tissue was to support structural maintenance of the gill filaments underneath the epithelia as a protective response to desquamation. Some samples showed cumulated mucous and particles on the filaments` tips.…”

Histopathological effects of the herbicide atrazine on gills of the Brazilian endemic bivalveDiplodon expansus

“…All animals of the control group survived the seven-day experiment and their gill filaments exhibited intact cells and other associated structures ( Figure 1A-E) as described for the species [40]. All animals exposed to different concentrations of atrazine survived the seven-day experiments.…”

“…In bivalve molluscs, the increase in mucus secretions is a very common response to the exposure to a toxic agent [18,23,40]. This response is usually associated with protection or defence mechanisms, as mucus might dilute toxins [42], thus removing toxic agents previously absorbed [50] and creating a barrier to prevent the entrance of toxic agents in damaged cells [24].…”

“…The samples were then dehydrated in a crescent series of acetone, immersed in resin:acetone solution (1:1) for 12 hours, embedded in Epon-araldite resin with catalyser for 24 hours and maintained in an oven at 70ºC for 24 hours for resin polymerisation. The material was sectioned with an ultramicrotome, sections were placed on copper screen and contrasted with uranyl acetate and lead citrate for later examination under electron transmission microscope Philips CM 100, operated at 80 kV [40].…”

Morphological Effects of Pollution on Gill of Common Clam, Tapes decussatus Linnaeus, 1758 (Bivalvia: Veneridae)

“…Several techniques have been used to assess the levels of pollutants in Bivalvia, including gill filaments morphology (Ballan-Dufrançais et al, 1990;Gold-Bouchot et al, 1995;Gregory and George, 2000;David and Fontanetti, 2005;Nogarol et. al., 2012).…”