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<title="chordatesandhemichordata"> <!stamp="chordatesandhemichordata-imp.jar 691231 19:00:00"> <s="Remaining Deuterostomes"> I will now finish the deuterostomes, beginning with the chordates, in which I include these groups: Craniata, Cephalochordata, and Urochordata. I will conclude with the hemichordates, which seem most likely to be more closely related to the echinoderms. <ss="Chordata = Urochordata , Cephalochordata, and Craniata"> <!slideid="100002"> These are the synapomorphies of the chordates. The Notochord is a support device. In some groups, like ours and the urochordates, the notochord is significantly reduced or lost. Chordates also have a particular nerve chord that is dorsally located and tubular. Chordates have gill slits. Like the notochord, these slits may be lost as the animal develops. The ancestral function of the gill slits were to filter water for feeding. Last but not least, chordates have a post anal tail. Chordates have tissue beyond their anus. This feature is also lost in some chordates. <ss="Urochordata (Tunicata) - ‘tailed’ chordates"> <!slideid="100003"> The first group I will talk about are the urochordates. These are often called tunicates because their bodies are covered by a jacket-like structure that resembles a tunic. Pictured in the upper right are examples of other tunic-wearing organisms. The strange thing about this tunic is that it is made up of connective tissue, yet it is external to the animal. Very strange. There are three classes of urochordates: The Ascideacea, the Thaliacea, and the Appendicularia. <ss="Ascideacea">
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<!slideid="100004"> ascidians look a bit like water pitchers. They can be solitary or live in colonies. Colonies in some ways resemble hydrozoan or anthozoan colonies. They are made up of individual zooids, but they are connected by tunic. Sometimes they share tunic. ascidians have a few well- developed organs, but most of their space is taken up by the pharyngeal basket, which is derived from the ancestral gill slits. Water is pumped in by cilia through the incurrent siphon at the top, it passes through the basket, food is trapped by mucus, and the water flows out the excurrent siphon, which looks like the pouring spout on the pitcher.
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