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Feb 21-Deuterostomia.docx

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Biology (Sci)
Course Code
BIOL 305
Virginie Millien

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Deuterostomata Phylogeny of deuterstome is quite stable: 2 main clades: Ambulacraria and Chordata Early development of echinoderms and chordates are very similar (embryological  evidence) Gill slits: big deuterostome invention ­ Concentrating ingested organisms that are smaller than you is difficult o you can trap them with a sticky trap with cilia and mucous (eg.  lophophorates) o you can rake them to sort out the larger particles (eg. barnacles) o you can strain them with perforations such that edible bits stay in and  water flows out  GILL SLITS!  Chordates: Tunicata (aka urochordata) ­ Mostly benthic/sessile ­ Colonial with extended individuality (could lead to specialization) ­ Eg. Oikopleura: planktonic with persistent notochord Cephalochordate: perhaps the sister group to chordates ­ Lay half buried in marine sediments ­ Myomered muscle segments to locomotion ­ Operates in a similar way to tunicates o Water goes in through the mouth through the pharynx and out the gill slits Chordates to be continued…. Ambulacraria: Hemichordates: ­ worm­like ­ burrowing or sometimes tube dwelling ­ body is regionated (somewhat “segmented”) o 3 regions that correspond to coelomic compartments ­ Pterobrachia: tube dwelling o Secrete a tube, half­buried o Always colonial o No prominent gill slits as an adult  Feed similarly to lophophorates ­ Enteropneusta: burrowing o 3 regions: proboscis, collar, tail/abdomen o coelom is used to extend the proboscis and as a hydrostatic skeleton Xenoturbellida: no brain, gut, more or less a bag of fluid with gonads and a mouth ­ Was first thought to be highly related to gastropods o Actually eats veliger larvae of welks, such that initial molecular  sequencing got it wrong o Is actually a deuterostome ­ Its phylogenic organization is pretty unknown (sister to echinoderms?) Echinoderms: lost almost all ancestral features that characterize deuterostomes ­ no gill slits ­ pentaradiates, but bilaterally symmetrical early in development ­ Larval development: o Bipinnaria o to brachiolaria (have longer arms that do not correspond to arms of the  adult o  to late brachiolaria (one end develops more and the rest is sloughed off) o at this point become pentaradially symmetrically  Sides of the larvae: Right = oral, left = aboral ­ We often think of the evolution as the process of developing complexity for  increased locomotive ease o Echinoderms have lost all of this complexity  o Bilateral symmetry, segmentation, brain/central nervous system, vascular  system, segmentation, eyes, gill slits, excretory system all lost o They’ve even done their best to lose their reproductive they just excrete  gametes into the sea ­ In exchanges they gained: o Water vascular system o Dermal ossicles ­ All large (smallest is like 1cm), unlike crustaceans o Due to hydrovascular system and dependence on hydraulics o If you get too small it doesn’t work o The larval stage allows it to get big all at
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