Characteristics of chordata1

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1. CHORDATES AND PROTOCHORDATES PRESENTED BY- HARI OM MSc. ZOOLOGY SEM-1 DEPARTMENT OF ZOOLOGY

2. CHORDATA Most advanced phylum 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

3. Animal belonging to Phylum Chordata are fundamentally characterized by: A notochord A dorsal hollow nerve chord Paired pharyngeal gill slits Post anal tail Presence of endostyle

4. Advancement of Chordata over 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

5. 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

6. Classification of Chordates The phylum 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

7. Hemichordata Hemichordata ( Acronworms )have been shunted 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.

8. Calcichordata The primitive stem-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 .

9. Urochordata “ Oura ” means Tail; Chor da 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

10. Continued…………….. Body is generally 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

11. Cephalochordata “ Cephalos ” means Head ; 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

12. 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

13. Reference Biology of Chordates Dr. Harish C. Nigam Modern Text Book of Zoology Prof. R. L . Kotpal www.biomentorsonline.com