Phylogeny I Chordate Origins

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Phylogeny I Chordate Origins
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Protochordates
Vertebrae
All four chordate characteristics retained
throughout lifetime
Notochord
Tadpole like larvae with post-anal tail
Dorsal Hollow Nerve Chord
Gill Slits
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Chordate characters
1- gill slits in pharynx
pharynx
gill bars
gill basket or pharyngeal basket
gill slits
gill bars
The pharynx is housed inside an atrium.
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1- gill slits in pharynx
Pharyngeal basket is primitively a feeding
structure
Used in filter feeding
Water enters mouth
Flows between gill bars
Food catches on gill bars
Water exits from pharynx via atriopore
Food is moved dorsally and ventrally by cilia,
then posteriorly to esophagus
gill basket or pharyngeal basket
gill slits
atriopore
gill bars
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1- gill slits in pharynx
Pharyngeal basket also used for filter feeding in
adult tunicate
Water and food enter incurrent siphon
Water is expelled through excurrent siphon
Food is trapped within pharynx and enters stomach
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Chordate characters
2- dorsal hollow nerve chord
Central part of nervous system
A hollow tube made up of neurons
Extends entire length of amphioxus and jawless
fishes
Always dorsal to notochord
dorsal hollow nerve chord
notochord
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notochord
notochord
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Dorsal hollow nerve chord
-notochord
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Chordate characters
3- post-anal tail
It works with muscles and notochord
To aid in mobility
Post- anal tail
anus
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Chordate characters
4- notochord
Central part of axial skeleton
A solid, stiff cartilage rod
Extend entire length of amphioxus and jawless
fishes
Always ventral to dorsal hollow nerve chord
dorsal hollow nerve chord
notochord
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gill arches
Myomeres (muscle segments)
and
Myosepta (the connective tissue between segments
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Classification of Deuterstomes
Phylum Chaetognatha
Phylum Echinodermata
Phylum Hemichordata
Phylum Chordata
Subphylum Urochordata
Subphylum Cephalochordata
Subphylum Vertebrata
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Phylum Hemichordata
Acorn worm
Have half of chordate characters
Gill slits in pharynx
Dorsal Hollow Nerve Chord
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Phylum Hemichordata
Detail of collar region
Gill slits in pharynx
Live in marine sediments
Dorsal Hollow Nerve Chord
Process sediment like an earth worm
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Subphylum Urochordata
tail chordates
Larvae have notochord restricted to tail
Also called Tunicates
tunic
For the tunic or jacket that covers the adult
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1) gill slits in pharynx
2) dorsal hollow nerve chord
Subphylum Urochordata
3) notochord
Free-swimming larva showing four
chordate characteristics
4) post-anal tail
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Two of four chordate characteristics lost in
tunicates during metamorphosis
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1500 species
Subphylum Urochordata
marine
Solitary tunicates
colonial tunicates
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But a variant (mutation) could have occured
Reproduction normally does not occur in larvae
That caused a timing change
HETEROCHRONY
Such that a larval form would be able to reproduce
Reproduction occurs here
Whats the evolutionary advantage?
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HETEROCHRONY
Different time
Changes in timing of events during
embryology. These are a major contributor to
evolution.
Paedomorphosis
Child-like morphology
Child-like morphology in an otherwise adult
organism Paedomorphosis can occur by two
mechanisms
Neoteny
new retaining
Organisms hold on to morphologies that they had
when they were new, but remaining systems become
adult.
Progenesis
early production
Organisms produce adult features in an otherwise
larval form.
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Subphylum Cephalochordata
-the product of progenesis?
This group retains chordate characters throughout
lifetime.
-named for extension of notochord into the
anterior (head) end
-NOT because it has a head
-cephalization is weakly developed
-no brain,
-no skull
-minimal sense organs
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Phylum Chordata
a monophyletic group
Vertebrae
All four chordate characteristics retained
throughout lifetime
Notochord
Tadpole like larvae with post-anal tail
Dorsal Hollow Nerve Chord
Gill Slits
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Subphylum Vertebrata
Larvae of the most primitive vertebrates,
the Agnatha or jawless fishes,
do not differ in basic body plan from
Amphioxus
or tunicate larvae.
This is the ammocoetes larva
of the lamprey
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Subphylum Vertebrata
-otic vesicle
hearing
Agnathan Larva
-eye
sight
The most significant differences are
-median nostril
smell
1) anterior swelling of DHNC
2) development of sense organs
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Subphylum Vertebrata
Adult Agnathan
(Lamprey)
-has an obvious head
-with additional sense organs
a pineal organ
senses light
a lateral line system
senses pressure and/or movement
Significant development of the head
(Cephalization) suggests alternate to the name
Vertebrata
Craniata