Tunicate

Abstract: The study of development and comparisons of the adult structures of the several groups of protochordate animals reveals something of their interrelationships and origin. The hemichordates are perhaps closer to the echinoderms than to the chordates, but these groups appear to have been derived from a bilaterally symmetrical dipleurula ancestor, not from a sessile pterobranch-like form. The origin of the chordates is speculative but the idea of a prototunicate stage is rejected. The tunicate is viewed as a highly modified end product, with fewer similarities to the ancestral form than amphioxus. Amphioxus is quite suggestive of the vertebrate, yet it is more like the tunicate in the details of its embryology and along with that rather extreme peripheral group is best thought of as constituting a subphylum, the Acraniata. The idea of the early vertebrate as a filter feeder must be rejected since it is assumed here that perfection of that function led to a sessile or inactive way of life (as in the acraniates or lamprey larva) and failed to lead to the active creature with highly developed sensory, neural, and locomotor systems identified here as the protovertebrate. Further, the muscular plastic pharynx and moveable mouth of the protovertebrate suggest feeding on larger organisms, predation, and the abandonment of ciliary water-current feeding.

Abstract: Ascidians (sea squirts) may defend themselves from predators, biofouling competitors, and bacterial infection by producing secondary metabolites or sequestering acid, but many species also accumulate heavy metals, most notably vanadium. The defensive functions of heavy metals in ascidians remain unclear, and to this end, the solitary Caribbean tunicate, Phallusia nigra, was studied to localize vanadium in its tissues and to assess the defensive properties of vanadium-containing compounds. As determined by flame atomic absorption spectroscopy, the internal tissues and blood contained the highest vanadium concentrations (mean values of 2280 and 1886 ppm dry mass, respectively), followed by the tunic surface (871 ppm dry mass). Results of laboratory feeding assays with the bluehead wrasse, Thalassoma bifasciatum, confirmed outcomes of past studies that demonstrated that vanadyl sulfate (VOSO4.6H20) and sodium vanadate (Na3VO4) were unpalatable to fish, although these salts do not accurately reflect the chelation environment or oxidation state of vanadium in living tunicates. Fresh preparations of whole tunic, internal tissues, and blood were unpalatable to fish, but freezing and thawing of internal tissues and blood rendered them palatable. Crude organic extracts of whole tunic and internal tissues contained vanadium metabolites (225 and 750 ppm dry mass, respectively) and were palatable to T. bifasciatum; crude extracts also exhibited no antimicrobial effects against a panel of four marine bacteria known to be pathogens of marine invertebrates (Vibrio parahaemolyticus, Vibrio harveyi, Leucothrix mucor, and Deleya marina). Nonacidic vanadium (+3) complexes neither deterred predation nor inhibited microbial growth, whereas acidic aqua vanadium (+3 and +4) complexes were unpalatable to 7 bifasciatum and exhibited antimicrobial activity. Difficulties in decoupling low pH from oxidation state and chelation environment of vanadium prevent definitive conclusions about the importance of some vanadium metabolites, but low pH appears to be the principal agent of chemical defense for P. nigra.

Abstract: The ascidian Cystodytes dellechiajei (Della Valle, 1877) (phylum Chordata, class Ascidiacea, family Polycitoridae) is a colonial tunicate that inhabits benthic rock environments in the Atlantic, Pacific and Indian Oceans, as well as the Mediterranean Sea. Its life cycle has two phases, the adult sessile colony and the free-living larva. Both adult zooids and larvae are surrounded by a protective tunic that contains several eukaryotic cell lines, is composed mainly of acidic mucopolysacharides associated with collagen and elastin-like proteins, and is covered by a thin cuticle. The microbiota associated with the tunic tissues of adult colonies and larva of C. dellechiajei has been examined by optical, confocal and electron microscopy and by fluorescence in situ hybridization (FISH), denaturing gradient gel electrophoresis (DGGE), and 16S rRNA gene clone library analysis. Microscopy analyses indicated the presence inside the tunic, both for the adult and the larva, of a dense community of Bacteria while only the external surface of colony cuticle was colonized by diatoms, rodophyte algae and prokaryotic-like epiphytes. Transmission electron microscopy showed tunic eukaryotic cells that were engulfing and lysing bacteria. 16S rRNA gene analyses (DGGE and clone libraries) and FISH indicated that the community inside the tunic tissues of the adults and larvae was dominated by Alphaproteobacteria. Bacteria belonging to the phyla Gammaproteobacteria and Bacteroidetes were also detected in the adults. Many of the 16S rRNA gene sequences in the tunic tissues were related to known aerobic anoxygenic phototrophs (AAP), like Roseobacter sp. and Erythrobacter sp. In order to check whether the gene pufM, coding for the M subunit of the reaction centre complex of aerobic anoxygenic photosynthesis, was being expressed inside the ascidian tissues, two libraries, one for an adult colony and one for larva, of cDNA from the expressed pufM gene were also constructed. The sequences most frequently (64% for colony and 67% for larva) retrieved from these libraries presented > 90% aa identity with the pufM gene product of the Roseobacter-like group, a cluster of AAP widely detected in marine planktonic environments.

Abstract: This report summarizes procedures that can be used to obtain high-quality reactivated motility of sperm flagella demembranated with Triton X-100. Although for years I have been reactivating sea urchin sperm flagella without exposing them to cyclic adenosine monophosphate (CAMP), the failure of these techniques to work with Ciona spermatozoa has led to the development of techniques involving incubation of demembranated spermatozoa with CAMP. This has led to the development of improved procedures for reactivating sea urchin spermatozoa, which give beat frequencies comparable to those of live spermatozoa. With both species, conditions can be found where a brief incubation with CAMP determines whether the spermatozoa are quiescent or fully motile when they are suspended in reactivation solution.