Characteristics of chordata1

Characteristics of chordata1

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  PRESENTED BY- HARI OM MSc.ZOOLOGY SEM-1 DEPARTMENT OF ZOOLOGY
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  CHORDATA  Most advancedphylum  Have around 48100 species  Humans are intelligent & dominating animal of chordata  Phylum chordata created by Balfour (1880)  Chorda means Cord; refers to presence of a stiff rod like structure called “Notochord”  Notes means Back ;Chorda means Cord
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  Animal belonging toPhylum Chordata are fundamentally characterized by:  A notochord  A dorsal hollow nerve chord  Paired pharyngeal gill slits  Post anal tail  Presence of endostyle
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  Advancement of Chordataover Non- Chordata  Living endoskeleton which grow with the body  More efficient respiratory organs (Gills/lungs)  More efficient circulatory system with well developed heart having cardiac muscles  Direction of blood flow first flows forward ventrally,then dorsally and backwords  Better sense organs and tubular nervous system  Endocrine glands for efficient chemical coordination
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  All Chordata are Triploblastic  Only two paired appendages  Bilateral symmetry  Deuterostomes  Coelomate  Organ system level of organization  Segmented body  Presence of Endostyle (Thyroid gland)  Ventral contractile heart
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  Classification of Chordates Thephylum Chordata is divided in to two subphyla :- Protochordata/Acraniata Vertebrata/Craniata Protochordata  Primitive Chordates  Exclusively marine  Vertebrae and paired appendages absent  On the basis of location of Notochord,divided in to four groups:- Hemichordata Calcichordata Urochordata Cephalochordata
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  Hemichordata  Hemichordata(Acronworms)have beenshunted from Non-Chordata or Chordates and vice-versa  In fact they should be placed as a phylum of Non-Chordata  Every effort to homologize a peculiar forword extension of the gut in to the proboscis of Hemichordates wiyh the notochord has failed to satisfy the modern zoologists Characteristic Features of Phylum Hemichordata  Hemichordata is bilaterally symmetrical and triploblastic animal.  They are exclusively marine animals.  They can be solitary or in colonies.  Hemichordata have a true body cavity or coelom.  The digestive tract is complete with an anus and can be in the form of a U shaped tube or straight.  A buccal diverticulum is present in the proboscis.  Body is divided into three regions – Proboscis, Collar and Trunk.  Circulatory system in open type.  Respiration occurs through gills.  The proboscis has a glomerulus, which is the excretory organ.  A primitive nervous system is present.  Sexes are separate or united.
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  Calcichordata  The primitivestem-chordates establishing a link between Echinoderms and the Chordates  All are fossils  They had a skeleton of calcite plates,like Echinoderms  A notochord ran the length of the pleated tail  In a groove above the notochord,a nerve cord was also present  Gill slits were present  Example:- Cothurnocystis & Mitrocystella.
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  Urochordata  “Oura” meansTail;Chorda means Cord  Notochord only present only in tail region of larva  Commonly called “Sea Squirt” or “Tunicates”  Exclusively marine ;solitary or colonial  Mostly sessile/fixed  Filter feeding  Nerve cord present in larva but replaced by a dorsal ganglion in adults  The pharyngeal slits are numerous ,persists in adults open in to an ectoderm lined cavity called “Atrium”  There are no gills  Retrogressive metamorphosis
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  Continued……………..  Body isgenerally covered or enclosed in a leathery bag like structure called “Tunic” or “Test”  Tunic composed of tunicin (similar to cellulose)  These animals are also known as Tunicata  Larva is more developed as compare to adult  Larva called tadpole (undergo retrogressive metamorphosis)  The Ascidian largest class of tunicates  Examples:- Herdmania ,Ascidia,Pyrosoma,Oikopleura
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  Cephalochordata  “Cephalos” meansHead ; Chorda means Cord  Members are commonly known as Lancelets  Only Cephalochordates having all four Chordate characters  Exclusively marine  Filter feeding  Notochord extends from head to tail region  Notochord persistent throughout their life but no brain formation  Numerous pharyngeal gill slits; persist in adults; open in to an Atrium instead of exterior  Tail persists throughout life
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  Continued………………  Small body(upto 5 cm ); elongated & laterally flattened  Nearly transparent tadpole creatures  Do not possess true heart ; major vessels pump blood  Dioecious; having numerous gonads  No asexual reproduction  Free swimming larva Examples:- Branchiostoma(Amphioxus/Lancelets)  Present in shallow Sea water  Long trunk , short tail  Tail bear caudal fin
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  Reference  Biology ofChordates Dr. Harish C. Nigam  Modern Text Book of Zoology Prof. R. L. Kotpal  www.biomentorsonline.com