1. Phylum Hemichordata (85 species) Class Pterobranchia (Sea Angels)
Class Enteropneusta (acorn worms)
Small group of marine worms that show similarities
to Echinoderms and Chordates

2. Tornaria of Acorn Worms Auricularia of Sea Cucumbers
Has a deuterostome embryology and resembles in ciliation
feeding mechanism (opposed band) and general appearance an auricularia larva of sea cucumbers
Also shares with echinoderms:
- Adult axial complex similarity (hemal –excretory system)
- Tripartite coelom

3. Adult Characteristics of Acorn Worms
3 partite coelom like echinoderms
Proboscis for digging (protocoel)
Stomochord first considered a notochord
Collar with mouth (mesocoel)
Main body is the trunk (metacoel)
Up to 100 pair of pharyngeal slits
N.S. An epidermal net…. Like the echinoderm nervous system but.. in some a dorsal hollow nerve cord

4. C H E Ch Hemi Echino Conflicting views of Deuterostome phylogeny
From Bromham and Degnan, 1999
Traditional Hemi + echino
C H E
Ch Hemi Echino
Pharynx
DNC
larvae
Axial
complex
Proto”D”
Proto”D”

5. C E H Conflicting views of Deuterostome phylogeny Fossil Stylophoran
From Bromham and Degnan, 1999
Fossil
Stylophoran
(Calcichordate)
C E H
Proto”D”
Hemichordate
Echinoderms

6. C H E C E H C H E Conflicting views of Deuterostome phylogeny
From Bromham and Degnan, 1999
Traditional Hemi + echino Calcichordate
C H E
C E H
C H E
Pharynx
DNC
larvae
Axial
complex
Fossil stylophoran
Proto”D”
Proto”D”
Proto”D”
-- Mitochondrial and 18s r-RNA sequence analysis strongly supports the Hemichordate-echinoderm (lineage Ambulacraria) relationship to the exclusion of the chordate clade.

7. C H E How is this possible??
Conflicting views of Deuterostome phylogeny
From Bromham and Degnan, 1999
Hemi + echino (Ambulacraria)
-- Hemichordates, Fossil Stylophorans, and Chordates all have pharyngeal slits and a dorasal nerve chord, but Echinoderms do not, yet Hemichordates are the sister group of Echinoderms and not of Chordates, and Stylophorans are more related to echinoderms then they are to chordates.
C H E
larvae
Axial
complex
Proto”D”
How is this possible??

8. 2008
Genesis 46:
Xenoturbella

9. Is not a basal deuterostome but rather the sister group of “Ambulacraria”