Branchiostoma lanceolatum: Amphioxus, the

‘lancelet’, subphylum Cephalochordata

And the invertebrate origins of the vertebrates:

Hemichordata & Urochordata

Protochordates

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

Determinate-Spiral as in

Protostomes

Blastopore

becomes anus, not

mouth

Starfish embryos:

egg – zygote –

cleavage – blastula

– gastrula –

bipinnaria.

mouth

anus

Echinoderm

bipinnaria larva

links them to

protochordates &

us!

Eumetazoa: Bilateria: Eucoelomata-Deuterostomes cont’d

Phylum Hemichordata

Phylum Chordata:

Subphylum Urochordata

Subphylum Cephalochordata

Subphylum Vertebrata

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

Subphylum Hemichordata: Balanoglossus

Hemichordata: Balanoglossus:

acorn worm-LS of “Head”

DHNC

Pharyngeal gill slits

collar

? ‘Notochord’/stomochord

Heart

proboscis

glomerulus

Halocynthia pyriformis

Subphylum Urochordata

In Larvaceae : gonads &

no sessile stage

Molgula occidentalis

46

Ant

ENDOSTYLE

Tentacular Filters

around Incurrent

Siphon

Esophagus

6 pairs of

Branchial Pleats

Cut Edge of

Mantle,tunic

removed

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

Finger print-like pattern of

stigmata in Molgula’s

Pharyngeal Gill Slits

Filtering

Tentacles

Around

incurrent

siphon

Didemnum candidum: A colonial Ascidian; an encruster

spicules

5 mm

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

Clavelina picta

Distaplia sp.

Tunicate larva

(Tunicate)

Larvaceae:

‘Oikopleura’?

Tunicate larva

Tunicate larva

Urochordata: Thaliacea: Salpa or Doliolum sp., ~1 mm

‘Salp’- Doliolum sp. in plankton tow net

~1mm – Thaliacea(Urochordata)

gonad

Muscular

ringsEndostyle

Buccal

siphon

Atrial

siphon

gut

tunic

Illustrations of burrowing lifestyle of

adults in sediment, filter feeding for

plankton, from internet

Pikaia gracilens was the oldest

known ancestor

cephalochordate from the 520

Ma middle Cambrian - Burgess

Shale of B.C. Canada

Artist’s rendition

fossil

Cilia in pharyngeal slits

Amphioxus

notochord

Branchiostoma floridae.: Larva in marine

plankton tow off Sarasota, FL

‘eye’

spot

mbl

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

Male w/ Testes

Female w/

Ovaries

notochord

Cilia in gill slit

Larval amphioxus in Sarasota,

FL plankton net tow~1mm

‘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

Metapleural folds

Wheel organs - ciliated

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

Branchial BAR

Branchial SLIT

Myosepta between Myomeres

Fin-ray

boxes

notochord

velum

Light sensitive receptors above notochord & in

center of to DHNC: OCELLI

Side view, optical section

OCELLI

Cross section

Dorsal, hollow nerve cord

notochord

Horizontal muscle fibers in notochord

maintain hydrostatic pressure and thus

firmness of notochord

notochord

Cilia on

Bars

Blood

vessels

coelom

Pharynx

Skeletal rod

ovary

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.

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”

Doral Aorta branch to

‘glomerulus’ ®

Solenocyte =

Podocyte

Bar

PHARYNX

Atria

SOENOCYTES (Podocytes)

the ‘flame cells’ or nephridia

of the Amphioxus

Nuclei of

Area of next slideWilley, 1894

caecum

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

Buccal Cirri

Oral hood

Fin-ray

box

DHNC

Notoch-

ord

Epidermis

Dermis

Hatschek’s

groove

Myomeres

Myosepta

coelom

mesoderm Neural fold & tube

blastula

invagination

blastopore

archenteron

notochord

After Cerfontaine & Hatschek, from Kellicott, 1913

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