Class Pterobranchia Sea Angels Class Enteropneusta acorn worms Small group of marine worms that show similarities to Echinoderms and Chordates Tornaria of Acorn Worms Auricularia ID: 927379
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Slide1
Phylum Hemichordata (85 species) Class Pterobranchia (Sea Angels) Class Enteropneusta (acorn worms)
Small group of marine worms that show similaritiesto Echinoderms and Chordates
Slide2Tornaria of Acorn Worms Auricularia ofSea Cucumbers
Has a deuterostome embryology and resembles in ciliation feeding mechanism (opposed band) and general appearance an auricularia larva of sea cucumbersAlso shares with echinoderms: - Adult axial complex similarity (hemal –excretory system) - Tripartite coelom
Slide3Adult Characteristics of Acorn Worms
3 partite coelom like echinodermsProboscis for digging (protocoel)
Collar with mouth (
mesocoel
)
Stomochord
first considered a notochord
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
Slide4C
h
H
emi
E
chino
C H E
Conflicting views of
Deuterostome
phylogeny
Pharynx
DNC
larvae
Axial
complex
From
Bromham
and
Degnan, 1999
Traditional Hemi +
echino
Proto
”
D
”
Proto
”
D
”
Slide5C
E H
Conflicting views of Deuterostome phylogeny
From Bromham and Degnan, 1999
Proto
”
D
”
Hemichordate
Echinoderms
Fossil
Stylophoran
(
Calcichordate
)
Slide6C H E
C H E
Conflicting views of
Deuterostome
phylogeny
C E H
Pharynx
DNC
larvae
Axial
complex
Fossil
stylophoran
From
Bromham
and
Degnan
, 1999
Traditional Hemi + echino Calcichordate
--
Mitochondrial and 18s r-RNA sequence analysis strongly supports the Hemichordate-echinoderm
(lineage
Ambulacraria
) relationship
to the exclusion of the chordate clade
.
Proto
”
D
”
Proto
”
D
”
Proto
”
D
”
Slide7C H E
Conflicting views of
Deuterostome
phylogeny
larvae
Axial
complex
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.
Proto
”
D
”
How is this possible??
Slide8Xenoturbella
2008
Genesis 46:580-586
Slide9Is not a basal deuterostome but rather the sister group of
“Ambulacraria”