Embryotoxic effects of organotin compounds on Styela plicata (Tunicata; Ascidiacea)

In order to clarify the interaction mechanism between organotin compounds and organisms, the effects of these compounds on the development of a benthonic filter-feeding invertebrate were studied. Embryos of the ascidian Styela plicata were obtained in laboratory by cross-fertilization and their development was followed in vivo after incubation with 0.1, 1, and 10 \u3bcM organotin compounds for various exposure times. Moreover, embryos selected at opportune stages after incubation with 10 \u3bcM tributyltin (TBT) or triphenyltin (TPT) for 1 hr were observed at the electron microscope to recognize cell alterations. Results indicate that organotins significantly affect all stages of ascidian development in a dose- and time-dependent manner and the most sensitive stages are gastrula and neurula. These compounds are able to block development, giving rise to anomalous embryos with irreversibile effects. The order of inhibition appears to be strongly dependent on the organotin liposolubility: TBT > dibutyltin (DBT) > monobutyltin (MBT) and TPT > tricyclohexyltin (TCHT). The mitosis block of blastomeres in the early stages may be related to an inhibition of the microtubule polymerization. Observations with light and electron microscopes reveal globeshaped blastomeres with large intercellular spaces in the morula and gastrula stages, suggesting a toxic damage with alteration of the cytoskeleton. Moreover, the occurrence of electron-dense precipitates of organotins in the inner membrane of mitochondria and morphological changes of their cristae suggest an inhibitory effect on oxidative phosphorylation which is conspicuous in the gastrula stage. In this stage, the size of the electron-dense aggregates grow from 50\u201370 to 110\u2013170 nm, while at the same time the alteration of the cristae increases

Paired gill slits in a fossil with a calcite skeleton

The chordates, hemichordates (such as acorn worms) and echinoderms (such as starfish) comprise the group Deuterostomia, well established as monophyletic 1,2. Among extant deuterostomes, a skeleton in which each plate has the crystallographic structure of a single crystal of calcite is characteristic of echinoderms and is always associated with radial symmetry and never with gill slits. Among fossils, however, such a skeleton sometimes occurs without radial symmetry. This is true of Jaekelocarpus oklahomensis, from the Upper Carboniferous of Oklahoma, USA, which, being externally almost bilaterally symmetrical, is traditionally placed in the group Mitrata (Ordovician to Carboniferous periods, 530–280 million years ago), by contrast with the bizarrely asymmetrical Cornuta (Cambrian to Ordovician periods, 540 to 440 million years ago). Using computer X-ray microtomography, we describe the anatomy of Jaekelocarpus in greater detail than formerly possible, reveal evidence of paired gill slits internally and interpret its functional anatomy. On this basis we suggest its phylogenetic position within the deuterostomes