What are protochordata?
Why are protochordata are primitive vertebrate
Shree jana Bomjan
Pema Tshojay
Kichu Lhaden
Protochordata( Acrania)
Vertebrata (Craniata)
1) Enteropneusta 1) Larvacea
2) Pterobranchia 2) Ascidiacea
3) Thaliacea
The name Protochordates literally means 'the first chordates’.
Protochordata - a heterogeneous group of animals of
phylum Chordata, related to the vertebrates, which they
resemble in possessing gill slits, noto-chord, and dorsal hollow
nerve cord, or at least traces of these.
Protochordates are marine animals
Why are protochordates not classified as true
• Like the remaining subphylum of the chordates, the Vertebrata, the
protochordates have a hollow dorsal nerve cord, gill slits, and a stiff
supporting rod, the notochord, the forerunner of the backbone.
The protochordates differ chiefly from the vertebrates in not having
a backbone.
Recent protochordates are thought to have evolved from the same
ancestral stock as that which gave rise to the vertebrates.
General characteristics of protochordata
• Exclusively marine.
• Relatively small sized animals
• Cranium or brain box, jaws, vertebral column and paired
appendages are absent.
• Dorsal tubular nerve cord, gill slits and notochord are usually
• Sexes may be separate or united.
• Solitary, colonial, free living, pelagic, burrowing or tube like
living forms
(A manual of practical zoology Chordates by P. S. Verma)
1) Hemichordata
The name Hemichordata refers to the presence of a short
notochord, reduced to half the size (hemi – half; chorde –
cord). This structure is present in the anterior region of
the animal, the proboscis
They include two groups;
1. Enteropneusta
2. Pterobranchia
General Characteristics of
 Exclusively marine and soft-bodied forms
 Body is divisible into proboscis, collar and trunk
 Notochord occurs only in the anterior end of the body.
 Numerous paired gill slits are present.
 Nervous tissues lie embedded in the epidermis and occur both on
the dorsal and ventral surfaces.
 Coelom is divided into three regions namely protocoel, mesocoel
and metacoel.
 Fertilization is external.
Class I- Enteropneusta
• Solitary and burrowing worm-like marine forms commonly
known as acorn or tongue worms.
• vegetation; filter-feeders
• They have well-developed gill slits
• Epidermis is ciliated and glandular.
• Alimentary canal is straight with a terminal anus.
• Two rows of caecae are present in the middle of the trunk.
• They have a dorsal strand of nerve cells
( A manual of Practical Zoology Chordates by P.S Verma)
Examples of Enteropneusta
Class II- Pterobranchia
 Sedentary, solitary or colonial and marine forms.
 Bears a ciliated tentacles to produce a Ciliary feeding currents
of water.
 One pair of gill slits or none.
 There is no trace of dorsal nerve cord or notochord
 Alimentary canal is U-shape with dorsal anus situated near the
 Gonads are few in numbers.
 Reproduction by budding.
( A manual of Practical Zoology Chordates by P.S Verma)
2) Urochordata
 Urochordata is the term used to refer to the presence of a
notochord in the tail region, (uro=a tail; chorde=cord).
 The notochord is restricted to the tail region of the larval forms
of urochordates and is absent in the adults.
 Tunicata is the other name of this subphylum Urochordata, due
to the presence of an outer leathery covering called tunic or
test in the adult (tunica – outer covering).
General characteristics of Urochordata
 Exclusively marine and commonly known as sea squirts.
 Solitary or colonial
 Body is covered by a cuticular tunics or test in adult stage.
 Notochord is present in larval stages and absent in adults.
 Dorsal tubular nerve cord is present in the larval forms while
degenerates in the form of small ganglion in adults.
 A numerous gill slits are present.
 Sexes are united that is hermaphrodite.
 Heart is ventral, simple and tubular.
Class I- larvacea
 Free swimming pelagic forms
 Neotenic forms which retain the larval form throughout adult
 Posterior part of the body takes the form of a large locomotory
appendage, the tail.
 Single pair of gill slits are present
 Anus opens ventrally on the surface of the body
 Hermaphrodite
 No metamorphosis.
( A manual of Practical Zoology Chordates by P.S Verma)
Examples of Urochordata
Class II- Ascidiacea
 Fixed or free swimming marine forms
 Simple or compound, solitary or colonial.
 Locomotory appendage or tail are absent in adults
 No traces of notochord
 Branchial sac is large and well developed with its walls
perforated by numerous gill slits.
 Reproduction is both asexual and sexual
( A manual of Practical Zoology Chordates by P.S Verma)
Class III- Thaliacea
 Free swimming pelagic forms.
 Solitary or colonial
 Musculature of the body wall is in the form of circular bands.
 Branchial sac has either two large or many small gill slits.
 Tail and notochord are absent in adult.
 Life history exhibits an alternation of generations.
( A manual of Practical Zoology Chordates by P.S Verma)
• The term Cephalochordata refers to the notochord that extends
the entire length of the body up to the head region (cephalon –
head; chorde – cord).
• The notochord lies on the mid dorsal region just above the
alimentary canal and below the nerve cord.
General characteristics
• Exclusively marine and solitary forms
• Notochord and nerve cord extend the entire length of the body.
• Notochord, nerve cord and pharyngeal gill slits remain
throughout life of the animal.
• Limbs or paired fins are absent.
• Mouth is ventral and anterior, while anus is ventral and posterior.
• No distinct head but tail present; mouth surrounded by
• Exoskeleton, head, brain, auditory organs and jaws are absent.
• Sexes are separate.
( A manual of Practical Zoology Chordates by P.S Verma)
Why are the protochordates so primitive
Chordates showing primitive features are collectively
grouped as protochordates.
• have a notochord, which is an elongate, stiff, fleshy structure
running down the length of the body, giving structure to the
body, enough so that muscles can fire down the body
enechelon to form the familiar "wiggly" swimming motion of
• The notochord is modified into the vertebral column in
vertebrate chordates.
• The nervous system is of a primitive nature, lying beneath the body
wall. Including a dorsal (toward the top of the body) nerve cord,
which is known as the spinal cord.
•Formed in the embryo by an invagination of surface ectoderm whose
original function was probably sensory reception.
•The ancestor was a fishlike deuterostome ( appears to form a natural
evolutionary line in which there are common features as well as
similarity in embryonic development) that swam using alternating
contractions of right and left longitudinal axial muscles to create
undulations of the body.
•Paired pharyngeal gill slits connect the lumen of the pharynx with
the exterior and originally functioned in suspension feeding with
respiration being added later.
Reference list
P.S. Verma. (1984). A Manual of Practical Zoology Chordates. New
Delhi: S. Chand and Company LTD.
Retrieved on 10th of May, 2011 from

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