EFFECTS OF TRIBUTYLTIN(IV) CHLORIDE EXPOSURE ON LARVAE OF CIONA-INTESTINALIS (UROCHORDATA) - AN ULTRASTRUCTURAL-STUDY

The effects of tributyltin(IV) chloride (TBT chloride) have been teste d on embryos of the ascidian Ciona intestinalis, at two different stag es of development: (1) before hatching (coiled larval stage) and (2) 2 h after hatching (swimming larval stage). In vivo observations carrie d out with a light microscope showed that embryos at the coiled larval stage did not hatch following exposure to TBT chloride. Severe anomal ies in the swimming larva, mainly concerning the morphology of the tai l, which appeared twisted and squatter than in the controls, were obse rved. Such anomalies were also found at a functional level, i.e. contr actile movements were poor so that the larvae appeared motionless. Ult rastructural investigations carried out using a transmission electron microscope (TEM) evidenced that the muscle cells of the tail were dama ged. Modifications mainly occurred in mitochondria and myofibrils, i.e . the energetic and enzymic centres. This fact is probably the main ca use of the loss of mobility of the larvae.