Chapter 25 - Chordates

Notes for Chapter 25: Chordates

Click link to return to Lecture Schedule
or back to Chapter 23
or ahead to Chapter 26

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

Source of Images

Featured Animal: Branchiostoma spp. (lancelet or "amphioxus")
More Links: 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8

Click link to return to Lecture Schedule
or back to Chapter 20
or ahead to Chapter 25 (not yet available)

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.

View source of image

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)

Click link to return to Lecture Schedule
or back to Chapter 23
or ahead to Chapter 26