The vanadium, iron, and manganese contents of 15 species of solitary ascidians belonging to the suborders Phlebobranchia and Stolidobranchia were determined by thermal neutron activation analysis. Vanadium was detectable in all species examined. In general, the vanadium content in various tissues of the Phlebobranchia was considerably higher than the iron and manganese contents. The blood cells especially contained a large amount of vanadium. The highest value (21 µg vanadium/mg dry weight) was obtained from blood corpuscles of Ascidia ahodori. Species in the suborder Stolidobranchia, on the other hand, had smaller quantities of vanadium in comparison with those in the suborder Phlebobranchia. The iron and manganese contents did not differ greatly between the two suborders. The data are considered in the light of physiological roles of these transition metals in ascidians.

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Ascidian blood cells contain a level of vanadium ion much higher than that in seawater. Blood cells are generally classified into six to nine types based on their morphology. On the basis of a Ficoll gradient for cell fractionation, neutron activation analysis of vanadium ion, and ESR spectra of oxovanadium ion in blood cells, the signet ring cells are the most likely

The Otx gene encodes a homeodomain transcription factor that has a highly conserved role in brain formation of both flies and vertebrates. To deduce evolutionary relationship of the chordate central nervous system to the larval or adult nervous system of nonchordate deuterostomes, we characterized the expression of the Otx gene (Sj-Otx) throughout the entire embryonic and larval development of the sea cucumber Stichopus japonicus. Sj-Otx transcripts were detected in fertilized eggs and in the posterior part of the archenteron of gastrulae. However, the expression was downregulated as embryos developed into auricularia larvae. Sj-Otx was expressed again in the ciliary bands of late auricularia larvae, just before metamorphosis to doliolaria larvae. The expression domain corresponded to the domains moving to the mouth during metamorphosis and sinking into the buccal cavity, but not to the five transverse ciliary bands of the doliolaria. The expression gradually disappeared during further development and was not detected in juveniles. These results indicate that the gene responsible for chordate brain formation is expressed in the ciliary bands of auricularia larvae.