PROTOCHORDATES
Hemichordates
Protochordates
Chordates
Cephalochordates
Urochordates
Vertebrates
1) Notochord
Hemichordate—acorn worm
2) Dorsal, hollow nerve cord
3) Pharyngeal slits
4) Postanal tail
5) other
Ciliary Mucous Feeder
(=suspension feeder, filter feeder)
*
*
1
Hemichordate—tornaria larva
Cephalochordate—amphioxus
Hemichordate
Cephalochordate—amphioxus
Cephalochordate—amphioxus
2
Hemichordates
Hemichordates
Cephalochordates
Cephalochordates—amphioxus
Tongue bar
Skeletal rods
Urochordate
“sea squirts”
“tunicates”
Urochordate—larva
3
Urochordate—larva
Urochordate—larva
metamorphosis
Amphioxus related to vertebrates?
Amphioxus
Ammocoetes larvae (Lamprey)
Vertebrate—lamprey
Lamprey larva—ammocoetes
4
Lamprey larva—ammocoetes
Origin of Chordate
Body Plan
Annelids
Origin of Chordate
Body Plan
Hubrecht (1883)
Arthropods
Annelid/arthropod
Annelid
Arthropod
Vertebrate
Patten & Gaskell
5
Echinoderms
Pharyngeal
slits
Larva
(Tornaria)
Larva
Embryology
Symmetry (bilateral)
Garstang
Garstang’s Mechanism
Selective Advantages
If larva gets BIGGER,
Mode of Locomotion
1, 2,
4
1, 4, 16
Cilia
Segmental muscles, notochord
1, 8, 64
Mode of Feeding
Adoral band Î Endostyle
Water Î Pharyngeal slits
Paedomorphosis
But,
Larval stage
Paedomorphosis
Juvenile + form
6
Garstang
Patterning
Genes
Dorsal
Genes
Ventral
Posterior
Anterior
Chordates ! ?
Genes
Dorsal
Genes
Ventral
7
Footnote
Paedomorphosis
8