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Lecture 16 � Bilateria � Acoelomates, Pseudocoelomates

Lecture 16 � Bilateria � Acoelomates, Pseudocoelomates

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Lecture 16 – Bilateria – Acoelomates, Pseudocoelomates Eumetazoa, have tissues. Not all organisms in bilateria are bilateral. Coelom used to be a huge way of grouping organisms but not anymore because of DNA A. Platyhelmithes – only phylum never questioned, they are acoelomate; they are flatworms (a lot of medically important infections are here) - Most primitive level of the bilateria Consists of 3 major groups: 1) Planarians 2) Flukes 3) Tapeworm - They are called flatworms because they are dorsoventrally flattened, elongated, and legless 1. Bilateria (fig. 30-1) 2. Caphalization – have a distinct head area (it is rudimentary, but it is there) - The importance’s of this: 1) We can move forward (have an anterior and posterior) In radial symmetry there is no forward direction 3. Three definite germ layers Triploblastic (everything from here on out if triploblastic) - The importance of this: 1) There are not muscles (can be much more complex) 4. Simple Organ Systems – pharynx, eyespots, brain, reproductive organs - Organ Level: we went from the Porifera (multicellular) Cnidarians (tissue) Platyhelminths (organ level) You have several tissues together that function as a unit - Besides organs, they have simple systems: a) Pharynx: muscular, used for grabbing food and swallowing b) Eyespots: look like eyes not really eyes, just sensory organs c) Brain: ganglia in the head area (a mass of nervous tissue; not complex)
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Planaria has 2 ganglia in the head and two ventral nerve cords (ventral is primitive, d is advanced; one cord is advanced, two cords are primitive) d) Reproductive Organs: very complex (which is why a lot of flatworm infections are widespread 5. Nervous System – brain, nerve cords 6. Excretory Structures – protonephridia (fig. 47-2)
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