Notes for Chapter 25: Chordates

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Chapter 25 Assignment: All RQ-25: 1-4, 6-8, 10
Also, see
Ch. 24: 486 (Cladogram of Deuterostomes)
Next: Ch. 26: 507-528; RQ-26: 3, 5-7, 13, 15-17
Then: Ch. 27: 538-548, 556-557; RQ-27: 1-3, 8-9, 12
Then:
Ch. 28: 559-571, 576-579; RQ-28: 2-5, 7, 10, 16-17
Then: Ch. 30: 609-621, 624-626, 634-639;
     RQ-30: 1-2, 6-8, 11, 15-16 (last two lectures)

Introduction: It's a Long Way from Amphioxus


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Featured Animal: Branchiostoma spp. (lancelet or "amphioxus")
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The following outline of lecture notes does not follow Ch. 25 headings.

Also note, the text cladogram figures have some problems. Here are more details.

I. Chordates:

Deuterostomia
  Unnamed clade 1
     Echinodermata (see Ch. 23)
     Hemichordata (see Ch. 24)
        Enteropneusta (acorn worms)
        Pterobranchia (pterobranchs)
  Chordata
     Urochordata (tunicates)
     Unnamed clade 2
        Cephalochordata (lancelets)
        Craniata (craniates)
           Myxini (hagfish)
           Vertebrata

 

The above classification reflects new views based on DNA sequence comparisons. Conventionally, hemichordates are sister taxon of chordates, not as sister taxon of echinoderms as above and in the cladogram below. This cladogram, from Billie Swalla, shows the current relationships, whereas Fig. 24-7 (p. 486) in text shows the conventional view. Swalla and colleagues have additionally proposed to separate urochordates from chordates as a separate phylum. This seems unnecessary and has not been followed here. Instead, they are treated, as is conventional, as a subgroup of chordates. So the "Chordates" label needs to be moved down to the node with the tadpole larva.


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Key Terms: gill slits, dorsal hollow nerve cord, notochord, postanal tail, endostyle, thyroxin, tunic, pharyngeal basket, larvacean, salp, lancelet, ammocoete larva (lampreys), Pikaia


Outline:
I. Overview of Chordate Relationships
     Chordate Classification Handout
II. Chordate Synapomorphies
III. Urochordates (sea squirts)
IV. Cephalochordates (lancelets)
V. Craniates (hagfish + vertebrates)

 

 

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This page created 11/4/01 © D.J. Eernisse, Last Modified 11/04/01, Links Last Completely Checked 11/04/01