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Topic: Urochordates

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	Urochordates
		Urochordates have a notochord that extends from just behind the head to the tail (rather than from head to tail; Urochordata means "tail-cord").
		This endows them both with a form of jet propulsion and a mechanism for filter-feeding (suspended food is removed from the water by the pharyngeal gill slits).
		Larvacians superficially resemble ascidian larvae and are the most specialized of the urochordates.
	cas.bellarmine.edu /tietjen/images/urochordates.htm (434 words)

	M20.htm
		Urochordates are found in a wide variety of body forms, lifestyles, and habitats.
		All are filter feeders, however, some tend to be benthic and sessile (such as the ascidians), others are pelagic and form important components of the zooplankton (the salps and the appendicularians).
		Thaliaceans are usually gelatinous, transparent urochordates, - which are more common in tropical and subtropical waters (however, there are species inhabiting the polar and temperate regions).
	www.meer.org /M20.htm (481 words)

	[Full text] Metaphylogeny of 82 gene families sheds a new light on chordate evolution
		Urochordates have been supposed to be a separate phylum from cephalochordates and vertebrates, but they were also described by some others as constituting a monophyletic group with lancelets (cephalochordates) [6].
		Cephalochordate and urochordate constituted a monophyletic group for 30.6% of the families, and urochordates were the closest relatives to vertebrates for 20.4%.
		The vertebrate genome is supposed to have undergone large-scale duplications, as it was observed in the human and the house mouse genomes [25].
	www.biolsci.org /v02p0032.htm (2817 words)

	Pharyngula::Urochordates and neural crest
		Urochordates are not considered to have anything like a true neural crest, a population of plastic, pluripotent migratory cells that adopt multiple fates in the organism.
		Alternatively, it is conceivable that urochordates are the true sister group of vertebrates and that the migratory cells evolved in their common ancestor after the divergence of amphioxus from the chordate lineage.
		Later in chordate evolution, probably at or near the base of the vertebrate radiation, the primitive migratory cells gained additional functions and/or were joined by other cell types to generate the multiple derivatives characteristic of the neural crest.
	pharyngula.org /index/science/comments/urochordates_and_neural_crest (923 words)

	Abstracts 49(1)
		Maximum parsimony, Neighbor-Joining, Minimum Evolution and Maximum Likelihood analyses of this large urochordate dataset are consistent with a topology in which the urochordates are monophyletic within the deuterostomes and there are four separate clades of urochordates.
		This is important because the tadpole morphology of larvacean and ascidian larvae is the key trait of interest that distinguishes urochordates as chordates.
		Nevertheless, the present data set resolves at least three clades of urochordates and suggests strongly that urochordates form a monophyletic clade within the deuterostomes.
	ag.arizona.edu /systbiol/SSBWeb/issues/49_1/abstracts49_1.html (1868 words)

	:::::: welcome to korean journal of biological sciences ::::::
		Urochordates, the most primitive group in phylum Chordata, are mostly sessile as adults although some are free living.
		Presently, the ancestral stock of urochordates as well as chordates has been the focus of interest and two conflicting hypotheses have been presented.
		To clarify the phylogenetic relationships within the urochordates, 22 urochordates and five others as outgroups were used.
	www.ibiosci.or.kr /kjbs/abstract.php?act=detail&code=KJBS0030403&page=1 (222 words)

	Evaluating Hypotheses of Deuterostome Phylogeny and Chordate Evolution with New LSU and SSU Ribosomal DNA Data -- ...
		White bars represent splits that neither occur in optimal ME trees nor are favored by spectral analyses of the combined data set; however, many of the competing hypotheses of deuterostome phylogeny are found in this category of splits.
		Note that split R represents monophyletic chordates and is to be compared with the split labeled Urochordates + Protostomes at far right, which was the next best alternative grouping for the urochordates.
		Swalla B. J., 2001 Phylogeny of the urochordates: implications for chordate evolution Pp.
	mbe.oxfordjournals.org /cgi/content/full/19/5/762 (6401 words)

	UCMP Glossary: S
		A natural depression in the surface of the land caused by the collapse of the roof of a cavern or subterranean passage, generally occurring in limestone regions.
		In many molluscs, the siphon may be used to expel water forcibly, providing a means of propulsion.
		They are structural components in many sponges, and may serve a protective function in other organisms.
	www.ucmp.berkeley.edu /glossary/glossary_S.html (1318 words)

	EVOLUTION/DEVELOPMENT: ON THE NEURAL CREST
		The neural crest arises at the dorsal aspect of the neural tube and then migrates widely in the embryo, giving rise to a range of derivatives which are distinctly vertebrate, such as the neurons and glia of the peripheral nervous system, melanocytes, and, additionally in the head, cartilage, bone and teeth.
		The results also have serious implications for how we view the relationships between the vertebrates, the cephalochordates, and the urochordates, as they suggest that it is the urochordates that are the true sister group of the vertebrates and not, as is generally accepted, the cephalochordates.
		Ciona has small larvae that exhibit the conventional mode of development; the larvae exist as free swimming members of the plankton, and during metamorphosis, the larval head attaches to the substrate, the tail is lost and the tissues of the head are reorganized into a sessile filter feeder.
	scienceweek.com /2005/sa050218-4.htm (1765 words)

	Interactive Fly, Drosophila
		The presence of a notochord unites urochordates, cephalochordates, and vertebrates, although some authors differentiate the notochord of vertebrates + cephalochordates from the urochord of urochordates.
		The characters that set vertebrates + cephalochordates apart from urochordates are the presence of myotomes in vertebrates + cephalochordates and the presence of the tunic in the urochordates.
		Urochordates are considered members of Chordata because the tadpole larva exhibits the chordate body plan.
	www.sdbonline.org /fly/aimain/tree.htm (555 words)

	Chapter 7 The Early Vertebrates
		Urochordates include tunicates or sea squirts, small boxlike creatures that live as adults in colonies fixed to the seafloor.
		The genome of the sea squirt is entirely compatible with their zoological placement near the base of the chordates.
		Another group of urochordates are the salps, which live in colonies that manage to swim.
	www-geology.ucdavis.edu /~cowen/HistoryofLife/CH07.html (1383 words)

	Tunicate - Wikipedia, the free encyclopedia
		Urochordata (sometimes known as tunicata and commonly called urochordates, tunicates, sea squirts or cunji) is the subphylum of saclike filter feeders with incurrent and excurrent siphons.
		There are also a few exceptions to this plan, like the predatory Megalodicopia hians, looking something like a cross between a jellyfish and a Venus Flytrap.
		Over the past few years, urochordates (notably of the genus Didemnum) have been invading coastal waters in many countries, and are spreading quickly.
	en.wikipedia.org /wiki/Tunicate (684 words)

	urochordate (Site not responding. Last check: )
		Evolution and Maximum Likelihood analyses of this large urochordate dataset are
		consistent with a topology in which the urochordates are monophyletic within the
		deuterostomes and there are four separate clades of urochordates.
	chuma.cas.usf.edu /~garey/urochordate.html (535 words)

	The Larvaceans (Class Larvacea)
		This tail, which contains the notochord is retained all through the animals life, unlike the rest of the Urochordates where it is lost before maturity, or even during embryogenesis.
		This 'house' encases the trunk or body, but not the tail, the tail has muscle cells attached to it and the Larvacean uses it to swim.
		This means that Larvaceans are one of the few animals to feed on the numerous coccolithophorids which abound in the oceans of the world.
	www.earthlife.net /inverts/larvacea.html (623 words)

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	www.essaytown.com /topics/urochordates_essays_papers.html (775 words)

	Molecular Phylogeny and Divergence Times of Deuterostome Animals -- Blair and Hedges 22 (11): 2275 -- Molecular Biology ...
		urochordates has also left evidence in the fossil record for
		urochordates are usually allied as chordates (Chordata) (R. Brusca and G. Brusca 1990
		to suggest a closer relationship between vertebrates and urochordates
	mbe.oxfordjournals.org /cgi/content/full/22/11/2275 (4781 words)

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