Larval development of Brachidontes solisianus (Bivalvia, Mytilidae): with notes on differences between its hinge system and that of the mollusk Perna perna

Este trabalho faz parte de um programa de estudo sobre larvas meroplanctônicas que tem como objetivo o reconhecimento mais preciso das larvas no plâncton. Este estudo foi iniciado com a espécie Brachidontes solisianus (Bivalvia - Mytilidae) que é muito abundante nos costões rochosos da região de Cabo Frio. O desenvolvimento larvar foi realizado sob condições controladas durante 26 dias. A alimentação foi feita com Isochrysis galbana e Tetraselmis chui. A temperatura e a salinidade foram mantidas a 26º C e 28 ë , respectivamente. Diariamente, as larvas foram desenhadas em câmara clara e medidas com ocular micrométrica até a fixação. A primeira fase de véliger em forma de "D" ou Prodissoconcha I, mediu em média, 90 µm de comprimento por 70 µm de altura e a última, antes da fase de fixação (Pedivéliger), mediu 273 µm de comprimento e 257 µm de altura. No estudo comparativo das charneiras, duas espécies foram consideradas: Brachidontes solisianus e Perna perna. Observou-se que a espécie B. solisianus apresenta dentes mais evidentes nas extremidades do provinculum, enquanto na espécie P. perna aparecem ao longo de todo o provinculum.

Surface morphology of Mytella falcata gill filaments from three regions of the santos estuary

Bivalves have been extensively used to monitor aquatic habitats because their sedentary filter feeding habit results in the accumulation of elements from the environment. The genus Mytella is of special interest because its habit of burrowing in sediments can provide information about the substrate conditions in estuaries. Gill filaments have a large surface that is in constant contact with the water and therefore are used to monitor aquatic environments. In this study, we used scanning electron microscopy (SEM) to investigate the morphology of Mytella falcata gill filaments and to compare the gill structure in specimens from three sites (A, B and C) of the Santos estuary in southeastern Brazil. Site A presents low levels of pollutants, whereas sites C and B were directly affected by industrial discharges and harbor pollutants. The gill filaments of M. falcata have three types of cilia, namely, lateral cilia, eu-latero-frontal cirri and frontal cilia. Structures joining the inner and outer lamellae were found on the abfrontal surface, in addition to the presence of composite and simple cilia. A comparison of the filaments of bivalves from the three sites revealed no morphological alterations, but there was an accumulation of mucus on the frontal surface of the gill filaments of specimens collected at site B. This mucus may function as a protective barrier against pollutants. Bivalves from site C showed no such alteration, even though this site had the highest levels of pollutants. This lack of alterations may reflect the fact that these specimens were collected from concrete pillars where there would be less contact with pollutants. Our findings may reflect a long-term adaptation of these mollusks to chronic exposure to pollutants.