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Branchiostoma lanceolatum: Amphioxus, the
‘lancelet’, subphylum Cephalochordata
And the invertebrate origins of the vertebrates:
Hemichordata & Urochordata
Protochordates
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Parazoa No tissues Porifera
Eumatazoa Radiata Diploblastic
Cnidaria/Ctenophora
Bilateria Triploblastic
Acoelomates Platyhelminthes/Nemertea
Pseudocoelomates Nematoda/Rotifera
Coelomates Protostomes Lophophorates/Mollusca/Annelida/Athropoda
Deuterostomes Chaetognatha/Echinodermata/Chordata
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Determinate-Spiral as in
Protostomes
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Blastopore
becomes anus, not
mouth
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Starfish embryos:
egg – zygote –
cleavage – blastula
– gastrula –
bipinnaria.
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mouth
anus
Echinoderm
bipinnaria larva
links them to
protochordates &
us!
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Eumetazoa: Bilateria: Eucoelomata-Deuterostomes cont’d
Phylum Hemichordata
Phylum Chordata:
Subphylum Urochordata
Subphylum Cephalochordata
Subphylum Vertebrata
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Pro
tos
tom
es
Ec
hin
od
erm
ata
‘Hem
ich
ord
ata
’
Uro
ch
ord
ata
Cep
halo
ch
ord
ata
Ag
na
tha
Cra
nia
ta
Deuterostomes
Protochordates Vertebrates
Branchial slits,
Dorsal Hollow Nerve
Cord, Notochord
Lower
Jaw
Chordata
No Lo.Jaw
Indeterminate, Radial
Cleavage
A simple Phylogeny of
Deuterostomes
No sessile adult
Head & vertebrae
2008: DNA sequences showed
Urochordates closer to Vertebrates
than Cephalochordates
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Subphylum Hemichordata: Balanoglossus
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Hemichordata: Balanoglossus:
acorn worm-LS of “Head”
DHNC
Pharyngeal gill slits
collar
? ‘Notochord’/stomochord
Heart
proboscis
glomerulus
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Halocynthia pyriformis
Subphylum Urochordata
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In Larvaceae : gonads &
no sessile stage
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Molgula occidentalis
46
Ant
ENDOSTYLE
Tentacular Filters
around Incurrent
Siphon
Esophagus
6 pairs of
Branchial Pleats
Cut Edge of
Mantle,tunic
removed
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R
L
Renal SacR. Ovary
R. Testes
Food Filled
Intestine
L. Gonads
Molgula
occidentalis:
sandy tunic
removed, organs
show through
‘mantle’
Hemal
vessels
Hermaphrodite=a
pair of ovaries &
testes
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Finger print-like pattern of
stigmata in Molgula’s
Pharyngeal Gill Slits
Filtering
Tentacles
Around
incurrent
siphon
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Didemnum candidum: A colonial Ascidian; an encruster
spicules
5 mm
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Gut
(intestine)
Gonads & ducts
endostyle
atrium
tunic
Blood vessel in ‘pedicle’
Ganglion or ‘brain’
Anus & sperm duct pore
esophagus
Pharynx w/ Gill SlitsEctinascidea sp.
stomach
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Clavelina picta
Distaplia sp.
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Tunicate larva
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(Tunicate)
Larvaceae:
‘Oikopleura’?
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Tunicate larva
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Tunicate larva
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Urochordata: Thaliacea: Salpa or Doliolum sp., ~1 mm
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‘Salp’- Doliolum sp. in plankton tow net
~1mm – Thaliacea(Urochordata)
gonad
Muscular
ringsEndostyle
Buccal
siphon
Atrial
siphon
gut
tunic
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Illustrations of burrowing lifestyle of
adults in sediment, filter feeding for
plankton, from internet
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Pikaia gracilens was the oldest
known ancestor
cephalochordate from the 520
Ma middle Cambrian - Burgess
Shale of B.C. Canada
Artist’s rendition
fossil
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Cilia in pharyngeal slits
Amphioxus
notochord
Branchiostoma floridae.: Larva in marine
plankton tow off Sarasota, FL
‘eye’
spot
mbl
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Pigment (‘eye’)
spotDHNC
ocelli
notochordpharynx
Pharyngeal, Visceral or
Branchial Barintestine
Myosepta between
Myomeres (‘Myotomes’)
Oral cirri
Oral Hood
Wheel
organ
Velum &
velar pore
Branchial
(Visceral,
Pharyngeal) Slit –
exits to
surrounding
Atrium
Endostyle
Digestive
Ceacum or’liver’
Atrial pore or
atriopore
Anus
Fin-ray box
Hatschek’s groove & pit
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Male w/ Testes
Female w/
Ovaries
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notochord
Cilia in gill slit
Larval amphioxus in Sarasota,
FL plankton net tow~1mm
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‘Caecum’, ‘Liver’ or midgut cecum
gut
Atrial pore (water exiting slits,
leaves atrium here)
Anusintestine
R L
Path of water through mouth, pharynx, slits
& atrium to pore
Ileocolic ring, a concentration of
intestinal cilia, because there is
no smooth muscle
Post anal
tail &
caudal fin
Dorsal fin
DHNC
Notochord
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Metapleural folds
Wheel organs - ciliated
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Aperture in velar
muscle wall
Ocelli
Wheel organ w/
ciliaOral hood
Ciliated oral cirri
Pigment spot
Dorsal hollow nerve
cordFin-ray boxes
NotochordVelar
tentacles
Hatschek’s pit & groove (ant.
Pituitary?)
Fin
Myomeres
No
cephalization
![Page 41: Protochordates - Mikrogeo · 2019-09-23 · Wheel organ Velum & velar pore Branchial (Visceral, ... of the Amphioxus Nuclei of. Willey, 1894 Area of next slide. caecum. Iliocolic](https://reader033.vdocuments.us/reader033/viewer/2022043001/5f78d7d2431846464d2c90f2/html5/thumbnails/41.jpg)
Branchial BAR
Branchial SLIT
Myosepta between Myomeres
Fin-ray
boxes
notochord
velum
![Page 42: Protochordates - Mikrogeo · 2019-09-23 · Wheel organ Velum & velar pore Branchial (Visceral, ... of the Amphioxus Nuclei of. Willey, 1894 Area of next slide. caecum. Iliocolic](https://reader033.vdocuments.us/reader033/viewer/2022043001/5f78d7d2431846464d2c90f2/html5/thumbnails/42.jpg)
Light sensitive receptors above notochord & in
center of to DHNC: OCELLI
Side view, optical section
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OCELLI
Cross section
Dorsal, hollow nerve cord
notochord
Horizontal muscle fibers in notochord
maintain hydrostatic pressure and thus
firmness of notochord
notochord
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Cilia on
Bars
Blood
vessels
coelom
Pharynx
Skeletal rod
ovary
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Caecum
Dorsal fin
Endostyle
Epibranchial groove
Food particles brought in through the oral hood and ‘mouth’ adhere to the endostylar
mucus and the mucus-food bolus is passed by the cilia upwards to the epibranchial
groove by the cilia of the branchial bars; hence backward to the ciliated gut.
Meanwhile the oxygenated water passes through the slits the atria and out the atrial
pore (atriopore). The caecum is believed to produce enzymes for digestion.
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Sections of
male (testes)
Left & female
(ovaries)
Right, section
is posterior
part of
branchial slits
and anterior
digestive
caecum”liver”
testesovary
Atrium
Pharynx
N
DHNC
endostyle
Epibranchial
groove
®
digestive
caecum”liver”
digestive
caecum”liver”
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Doral Aorta branch to
‘glomerulus’ ®
Solenocyte =
Podocyte
Bar
PHARYNX
Atria
SOENOCYTES (Podocytes)
the ‘flame cells’ or nephridia
of the Amphioxus
Nuclei of
![Page 48: Protochordates - Mikrogeo · 2019-09-23 · Wheel organ Velum & velar pore Branchial (Visceral, ... of the Amphioxus Nuclei of. Willey, 1894 Area of next slide. caecum. Iliocolic](https://reader033.vdocuments.us/reader033/viewer/2022043001/5f78d7d2431846464d2c90f2/html5/thumbnails/48.jpg)
Area of next slideWilley, 1894
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caecum
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Iliocolic band of concentrated cilia to
move digestive bolus to anus, because the
‘intestine‘ has no muscle for peristalsis;
note bolus in center.
atria
intestine
Cephalic Caudal
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Buccal Cirri
Oral hood
Fin-ray
box
DHNC
Notoch-
ord
Epidermis
Dermis
Hatschek’s
groove
Myomeres
Myosepta
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coelom
mesoderm Neural fold & tube
blastula
invagination
blastopore
archenteron
notochord
After Cerfontaine & Hatschek, from Kellicott, 1913
See next
page
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