Protochordates and the Origin of the

Phylum Echinodermata
Chordates • Unique calcium carbonate skeleton
• Secondary radial symmetry in adults
• Bilateral symmetry in early life stages

Phylum
Deuterostomes Echinodermata Sea urchin
Sea daisy

• Ernst Haeckel (1874) proposed a • Unique calcium Starfish

taxonomic classification of deuterostomes carbonate skeleton Sea cucumber Crinoid

• Also known as enterocoelomates because • Secondary radial

their coelom develops through enterocoely symmetry in
adults
• Bilateral
Four extant phyla:
symmetry in early
• Xenoturbellida life stages
• Echinodermata
• Hemichordata Phylum
• Chordata Hemichordata
• Commonly
Protochordates known as acorn Bateson’s
• Closest relatives of vertebrates along with worms considerations
the hagfish • Vermiform placing Phylum
• Provide clues to the invertebrate origin of bottom dwellers Hemichordata under
found in shallow Phylum Chordata
animals with backbones
mud water 1. Collar nerve cord
• Fragile and can is dorsally located
Composed of: with lumen
• Hemichordata reach up to 5 feet
in length 2. Have slits that
• Urochordata open to the exterior
• Cephalochordata • Proposed
classification: in lateral walls of the
• 1870 Gregenbaur foregut
- Enteropneusta 3. Have a
Different Chordate larva stomochord, short
• 1874 Haeckel -
Phylum Chordata diverticulum of the
• 1884 Bateson - foregut findings
Subphylum ultimately showed
Hemichordata that it is not
homologous to the
chordate notochord

Share characters
with both
echinoderms and
chordates
• Pharyngeal slits
(chordates)

Mika Mendoza BSBCHEM

 • Diffuse epidermal system that
nervous system connects with
(echinoderms) series of gill
• Tripartite coelom slits in sides of
(echinoderms) pharynx
• Buccal  Primarily
diverticulum is now ciliary-mucus
believed to be a feeders using
synapomorphy of U- shaped gill
hemichordates only slits
Middorsal vessel
• Sequence analysis expands into a sinus
of the gene encoding and heart vesicle
the small subunit of above the buccal
rRNA supports a diverticulum
deuterostome clade • Blood enters network
• Echinodermata of blood sinuses called
• Hemichordata glomeruli and then
• Chordata through an extensive
system of sinuses to
Class Enteropneusta the gut and body wall
• Wormlike acorn • Nervous system
worms consists mostly of a
• Mucus-covered body subepithelial plexus
• Active proboscis  Dorsal nerve
collects food in cord
mucous strands (neurocord)
• Cilia carry particles formed by an
to groove at the edge invagination of
of the collar, then to ectoderm
the mouth (hollow in
• Thrust proboscis into some species)
mud and ingest mud to  Sexes are
extract the organic separate
matter  Fertilization is
• Buccal diverticulum external
connects protocoel  In some
with a proboscis pore species a
to the outside ciliated
• Contraction of body tornaria larva
musculature forces develops
excess water out similar to that
through the gill slits of echinoderm
 Roll of gill larva
pores is part of  At least one
branchial species
Mika Mendoza BSBCHEM
 undergoes • Marine
asexual chordates
reproduction •
Notochor
d is found
Class Pterobranchia in the
Basic plan similar to locomotiv
that of Enteropneusta e tail of
• Small animals, the free-
usually 1 to 7 mm in living
length larval
• Many individuals stage
may live together in •
collagenous tubes Enclosed
(zooids are not in tunics
connected) • Filter
• Body divided into feeders
three regions: Three
proboscis, collar and classes:
trunk •
• Ciliated grooves on Ascidiace
tentacles and arms a
collect food •
• Both dioecious and Larvacea
monoecious species •
• Asexual Thaliacea
reproduction is by
budding Class Ascidiacea
• Sea squirts are the best known
Similarties between hemichordates and urochordate
echinoderms • Can either be solitary or colonial
1. Bilaterallysymmetricallarvae • Larvae are tiny and have a fleeting
2. Similarincertaindevelopmentalprocesses, existence lasting for a few minutes to a
in muscle proteins, etc. few days and do not feed
3. In addition to the dorsal nerve cord, there • Presence of uninucleated striated
is another one on the ventral surface, as in muscles
invertebrates
4. Deuterostomous development • Respiratory water  mouth 
pharynx  gills  atrium  atriopore
Subphyl • Adhesive papillae attaches the larva
um to a permanent substrate
urochord • Notochord is resorbed and becomes
ate source of nutrients during
NOTOC metamorphosis
HORD!!

Mika Mendoza BSBCHEM

 • Nervous system location is altered Adult sea squirts retain 2 of 5 chordate
and rearrangement of viscera takes features:
place • Pharyngeal slits
• Larval mouth becomes the incurrent • Endostlye
siphon (anterior) while the atriopore • Tadpole larvae have all 5 chordate
becomes the excurrent siphon (dorsal) characteristics
• Called sea squirts because they Class Larvacea
discharge a jet of water when disturbed • Planktons on surface water or deep
sea
Class Ascidiacea • With a long body and a long flat
• Water entering the incurrent siphon locomotive
passes through a ciliated perforated tail supported by a notochord
pharynx with an elaborate basketwork • Retain larval form yet is sexually
• Water flows through slits into atrial mature
cavity and out through excurrent • Resemble the larval stages of other
siphon urochordates
-Surrounded by a thick, delicate hollow
sphere of mucus interlaced with
passages for water entry produced by
the larva
• Phytoplankton and bacteria trapped
on a feeding filter inside the sphere are
drawn into the branchial basket
• Feeding depends on the formation of through pulsating movement
a mucous net that is secrete by the • When filters become clogged with
endostyle wastes, they are left behind and a new
• Cilia on gill bars of pharynx pull sphere is built
mucus into a sheet Class Thaliacea
• Particles trapped in sheet are worked • Free-living (sexual) and colonial
into a rope and carried back to the (asexual) in alternate generations
esophagus and stomach • Resemble adult sea squirts in terms of
• Polyp becomes a filter feeder branchial basket
• Cylindrical in shape with the siphons
 Heart drives blood first in one on both ends of the cylinder
direction, then in reverse • Movement by jet stream from
 Nervous system has one nerve excurrent siphon
ganglion and a plexus of nerves  No notochord has been
on dorsal side of pharynx described
Class Thaliacea
 Subneural gland samples
incoming water and may have
an endocrine function
• Hermaphroditic with a single ovary
and a single testes and fertilization is
external

Mika Mendoza BSBCHEM

 • Food is moved through gut
via cilia concentrated in areas
called the ileocolic ring
Closed circulatory system is
complex but lacks a
Heart
• Blood lacks erythrocytes
and hemoglobin and mainly
transports nutrients
• Hollow nerve cord lies
above the notochord
• Pairs of spinal nerve roots
Subphylum emerge at each trunk
Cephalochordata segment
• Sense organs are simple,
• Generally called amphioxus including an unpaired ocellus
(sharp at both ends) or that functions as a
lancelet (little spear) photoreceptor
• Genera: Branchiostoma and • Anterior nerve cord is not
Asymmetron enlarged, yet is homologous
• Marine forms in sandy to vertebrate brain
beaches
• Filter feeders by burrowing • Sexes are separate
in the sand, making a U-turn • Gametes are set free in the
and having the oral hood atrium and pass
protruded out through atriopore
• Fertilization is external
• Larvae soon hatch and
gradually assume the shape of
adults
• Amphioxus possesses
features that suggest the
vertebrate plan
• Cecum is a diverticulum
resembling the vertebrate
pancreas in secreting
• Water enters the mouth digestive enzymes
directly driven by cilia in • Trunk muscles resemble
the buccal cavity and vertebrate patterns
pharynx • Posses basic circulatory
• Water passes through plan of vertebrates
pharyngeal slits where food
is trapped in mucus secreted Differences with Similarities with
vertebrates vertebrates
by the endostyle
1. Almost no 1. Big five
cephalization
Mika Mendoza BSBCHEM
 and no paired 2. Segmented or
sense organs metameric
2. Novertebral musculature
• Dorsal hollow nerve cord develops as
column 3. Two layered of the amphioxus but with a tripartite
3. Has pharyngeal skin brain
slits in large 4. Blood flow
numbers direction in
• Seven pair of gill slits open to the
4. Brain lacks arterial and exterior for respiration
major craniate venous channels • Skin is multilayered
subdivisions 5. Homologous
5. Segmented homeobox gene
• Body wall musculature provides
musculature clusters locomotion
extends to the • Filter feeders
anterior tip of
the head
6. One-layered • Food particles are trapped in mucus
external produced by the endostyle which is
integument
7. Nomuscular
homologous to the hypobranchial
heart groove of amphioxus
8. Coelomis found • Hypobranchial groove in ammocoetes
in adult forms
only
sink and becomes the subpharyngeal
gland
• Ammocoetes have a solid liver
diverticulum which the amphioxus has a
Subphylum Cephalochordata saccular diverticulum at the same
• Fossil cephalochordates have been found location but are not analogous
in very old rocks, indeed, predating the
origin of the vertebrates The Origin of the Craniates
• Yunnanozoon - earliest known
cephalochordate found in South China
(Early Cambrian) Ostracoderms
• Pikaia - cephalochordate fossil found in
BC, Canada (Middle Cambrian) • Bottom-dwelling organisms from the
• Cathaymyrus - eel-like; earliest known Late Cambrian
chordata fossil somewhat similar to Pikaia • Sucked up organic material from the
sediment like vacuum cleaners
AMMOCOETE LARVA • Most ancient agnathan or jawless fish
 Shows evidence that vertebrates • Extinct by the Devonian because they
share a common ancestor with could not compete with other jawed
protochordates fishes
• Notochord that commence from the
midbrain and continues to the end of
the body (no vertebral column)

Mika Mendoza BSBCHEM

Mika Mendoza BSBCHEM