Phylum chordata and protochordates

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PRESENTED AND PREPARED BY

• SADIA KHURSHID
• LECTURER ZOOLOGY DEPARTMENT
• DA COLLEGE FOR WOMEN,PHASE VIII
  

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PHYLUM CHORDATA (Protochordates)

• INTRODUCTION, CLASSIFICATION AND GENERAL
  CHARACTERS OF CHORDATES AND PROTOCHORDATES

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OUTLINE

• Definition
• Fundamental characters
• General characters
• Classification of chordata
• Group Acraniata
• UROCHORDATA
• More details
• Systems
• CEPHALOCHORDATA
• SYSTEM

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DEFINATION

• The name of this phylum is derived from two
  Greek words, the chorde meaning a string or cord,
  and ata meaning bearing, group or forms.
• Thus chordates are animals having a
  cord , i.e., notochord.

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CHORDATES

• They include about 45000species including many
  animals of major economic importance.
• Phylum Chordata includes the most highly evolved
  animals, the vertebrates, as well as the marine
  invertebrate cephalochordate, amphioxus and
  tunicates.

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FUNDAMENTAL CHARACTERISTICS OF CHORDATES

• All chordates shows all or at least any one of
  the following three fundamental characteristics
• Notochord
• Nerve cord
• Pharyngeal gill slits

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1-NOTOCHORD(chorda dorsalis)

• DEFINATION
• The notochord is an elongated, flexible
  cartilaginous rod-like, skeletal structure lies
  dorsal to the gut tube and ventral to the nerve
  cord.

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DIAGRAM OF NOTOCHORD
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Fates of notochord

• In most adult chordates the notochord disappears
  or becomes highly modified, or it is surrounded
  and replaced by a vertebral column.
• In some non-vertebrate chordates and fishes the
  notochord persists as a laterally flexible but
  incompressible skeletal rod.

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FIGURE 1 A generalized chordate showing
fundamental chordate characters
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2-NERVE CORD

• DEFINATION
• The nerve cord of chordates develops dorsally
  in the body as longitudinal, a fluid filled
  hollow tube, lying just above the notochord and
  extending lengthwise in the body.

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Fates of nerve cord

• In most species it differentiates in
  embryogeny into the brain anteriorly and spinal
  cord that runs through the trunk and tail.
  Together the brain and spinal cord are the
  central nervous system to which peripheral
  sensory and motor nerves connect.

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3-PHARYNGEAL GILL SLITS

• DEFINATION
• In all chordates, at some stages of their life
  history, a series of paired lateral gill cleft or
  gill slits perforate through the pharyngeal wall
  of the gut behind the mouth. These are variously
  termed as branchial, visceral or pharyngeal cleft
  or pouches.
• The soft and skeletal tissues between
  adjacent clefts are the visceral arches. (FIGURE.
  1)

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Function of gill cleft

• Gill cleft serve primarily for the passage of
  water from the pharynx to outside , thus bathing
  the gills for respiration.
• The water current secondarily aid in filter
  feeding by retaining food particles in the
  pharynx.

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Embryonic fate of the clefts

• Non-vertebrate chordates The clefts and
  arches are elaborated as straining devices
  concerned with capture of small food particles
  from water and are function throughout life.
• Fish-like vertebrates and juvenile amphibians
  The walls of the pharyngeal clefts develop
  into gills that are organs of gas exchange
  between the water and blood.
• Adult amphibians and the amniotes tetrapods
  The anterior most cleft transforms into the
  auditory tube and middle ear chamber, whereas the
  other clefts disappear after making some
  important contributions to glands lymphatic
  tissue in the throat region.

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GENERAL CHARACTERISTICS OF CHORDATES

• Chordates in general have following
  characteristics
• Bilateral symmetry
• Triploblastic
• Deuterostome
• Complete digestive tract
• Well developed coelom
• Internal organs are suspended in the coelomic
  cavity by a thin membranous tissue called
  mesentery
• Sexual reproduction
• Post anal tail

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CLASSIFICATION OF CHORDATES
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1-Group ACRANIATA (Protochordata)

• They are the simple or first chordates in which
  brain box (cranium) is absent and hence brain is
  not prominent.
• Notochord does not transform into vertebral
  column.
• Group acraniata is divided into two sub
  phylum
• Urochordata (notochord in the tail)
• Sub-phylum cepalochordata (notochord from head to
  tail)

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1-SUB-PHYLUM UROCHORDATA (Tunicata)

• Urochordates have a notochord that extends from
  just behind the head to the tail (rather than
  from head to tail Urochordata means
  "tail-cord").
• Urochordates are also called tunicate because
  their body is enclosed in a sac called tunic or
  test composed largely of tunicine, similar to
  cellulose. (FIGURE-2) Tunicate includes about
  2,000 fixed and nearly 100 pelagic species.

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FIGURE 2 Tunicates sea squirts
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More about Urochordates

• DIGESTIVE SYSTEMThey are all marine and sessile.
  Most tunicates feed by filtering sea water
  through pharyngeal slits.Tunicates are suspension
  feeders. They have two openings in their body
  cavity, an in-current and an ex-current siphon.
  The in-current siphon is used to intake food and
  water, and the ex-current siphon expels waste and
  water.
• The tunicate's primary food source is plankton.
  Plankton gets entangled in the mucus secreted
  from the endostyle.The tunicate's pharynx is
  covered by miniature hairs called ciliate cells
  which allow the consumed plankton to pass down
  through to the esophagus. Their gut is U-shaped,
  and their anuses empty directly to the outside
  environment. They have complete digestive
  tract.(FIGURE-3)

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Figure 3 Internal organs of adult ascidians
(sea squirt). Large arrows show water flow
through the animal small arrows, the path food
trapped by the pharyngeal gill slits takes
through the animal.
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RESPIRATION, EXCRETION AND COELOM

• RESPIRATION They have two to seven pairs of gill
  slits. Respiration through test and gill slits.
• EXCRETION Tunicates lack the kidney-like
  metanephridial organs. They have neural gland,
  pyloric gland and nephrocytes.
• COELOM The original coelom body-cavity develops
  into a pericardial cavity and gonads.

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What the Urohordates have?

• Like other chordates, tunicates have a
  notochord during their early development, but
  lack myomeric segmentation throughout the body
  and tail as adults.
• Blood vascular systemBlood vascular system is
  of open type. Heart is simple, ventral and
  tubular. Tunicate blood contains high
  concentrations of the metal vanadium
  ,vanadium-associated proteins as well as lithium.
  

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REPRODUCTION

• Most tunicates are hermaphrodites. Tunicates
  begin life in a mobile larval stage that
  resembles a tadpole, and exhibit chordates
  characters. It contains a nerve cord and a short
  notochord in its tail only .
• As the larva reaches maturity it attaches to the
  sea bottom and undergoes retrogressive
  metamorphosis by losing its tail and most of the
  chordate characters.only gill slits persist.
  Later, it develops into a barrel-like and usually
  sedentary adult form. (FIGURE-4)
• IN PAKISTAN
• Many species of Herdmania are fond in our
  seas.

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FIGURE 4 LARVAL AND ADULT ASCIDIAN
Ascidian Larvae
Older Ascidian Larvae
Young Ascidian Larvae
Adult Ascidian
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2-SUB-PHYLUM CEPHALOCHORDATA

• DEFINATION
• Cephalochordates are small, eel-like animals
  that spend much of their time buried in sand.
  They have notochord and nerve cord extends from
  head up to the tail, and persists throughout life.

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Chordates features

• Cephalochordates have all the typical chordate
  features.
• dorsal nerve cord
• notochord.
• pharyngeal slits (100 )which are used to strain
  food particles out of the water.
• The musculature of the body is divided up into
  V-shaped blocks, or myomeres.
• post-anal tail.
• On the other hand, cephalochordates lack features
  found in most or all true vertebrates, small
  brain and poorly developed sense organs and no
  true vertebrae.
• (FIGURE-5)

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FIGURE 5 AMPHIOXOUS
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DIGESTIVE SYSTEM

• Digestive tract is complete. Pharynx is large
  perforated by numerous gill slits. They are
  filter feeder.
• A pouch or hepatic caecum secretes digestive
  enzymes, and actual digestion takes place in a
  specialized part of the intestine known as the
  iliocolonic ring. (FIGURE -6)

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FIGURE 6 AMPHIOXOUS INTERNAL STRUCTURE
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More about cephalochordates

• RESPIRATION Respiration through the general body
  surface. No special organ for respiration.
• CIRCULATORY SYSTEM Cephalochordates also have a
  well-developed circulatory system.
• EXCRETORY SYSTEM Simple excretory system
  composed of paired nephridia.

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REPRDUCTION

• Reproduction is sexual. The sexes are
  separate, and both males and females have
  multiple paired gonads. Eggs are fertilized
  externally, and develop into free-swimming,
  fishlike larvae. No asexual reproduction.
  Development is indirect.

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SPECIES NUMBERS

• Cephalochordates comprises about 30 species.
• IN PAKISTAN
• Out of only two genera found around the world,
  Branchiostoma is found on our coast.

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REFERENCES

• WEBSITE USED
• www.wikipedia.com
• www.youtube.com
• www.google.com
• www.glossary.com
• www.answer.com
• BOOKS
• Elements of Chordate Anatomy by Charles K.
  Weichert
• Modern Text Book of Zoology, Vertebrates. R.L.
  Kotpal

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• Thank you