What are protochordata?

Why are protochordata are primitive vertebrate

Presenters;

Shree jana Bomjan

Pema Tshojay

Kichu Lhaden

Phylum-Chordata

SubphylaProtochordata( Acrania)

Subphyla Vertebrata (Craniata)

hemichordata Urochordata Cephalochordata

1) Enteropneusta2) Pterobranchia

1) Larvacea2) Ascidiacea3) Thaliacea

Protochordata

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

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Why are protochordates not classified as true Chordata

• 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.

http://wiki.answers.com/Q/Why_are_protochordates_not_classified_as_true_cho

rdates#ixzz1MathrUsV

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

present.

• 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 hemichordates

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

BalanoglossusSaccoglossus

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 mouth.

Gonads are few in numbers.

Reproduction by budding.

( A manual of Practical Zoology Chordates by P.S Verma)

)

cephalodiscus

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

life.

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

Oikopleura

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)

Ciona

Ascidia

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)

Doliolum

Cephalochordata

• 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 tentacles

• Exoskeleton, head, brain, auditory organs and jaws are absent.

• Sexes are separate.

( A manual of Practical Zoology Chordates by P.S Verma)

amphioxus

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

fish.

• 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.

(http://lander.edu/rsfox/invertebrates/branchiostoma.htm/)

Reference list

P.S. Verma. (1984). A Manual of Practical Zoology Chordates. New

Delhi: S. Chand and Company LTD.

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