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HEMICHORDATA 2Nd Sem (C3T) HEMICHORDATA 2nd Sem (C3T) Dr. Ranajit Kr. Khalua Assistant Professor Dept. zoology Narajole Raj College Paschim Medinipur GENERAL CHARACTERS 1. Exclusively marine worm like and soft-bodied animals. 2. Body is divisible into proboscis, collar and trunk. 3. Notochord Occurs only in the anterior end of the body. Recently it has been called “buccal diverticulum” due to its doubtful nature. 4. Numerous paired gill slita are present. Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College 5. Nervous tissues lie embedded in the epidermis and occur both on the dorsal and ventral surfaces 6. Coelom is usually divided into three distinct portion corresponding to the three regions. 7. Blood vascular system is simple . 8. Sexes are separate and the development may be direct or indirect. Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College Classification Hemichordata has been divided into following four classes : Class 1. Enteropneusta I. Solitary and burrowing worm-like marine forma commonly known as "acorn” or 'tongue worm . II. Body consists of the usual divisions viz., proboscis Separated by the narrow stalk from the ring Shaped collar, which is succeeded by an engated trunk. III. epidermis is ciliated and glandular. IV. Numerous gill sants and gonads are present. V. Alimentary canal straight with a terminal anus. Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College Example : Saccoglossus and ptychodera Fig : Saccoglossus Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College Class 2. Pterobranchi I. Sedentary, solitary or colonial and marine form. II. Proboscis bears ciliated tentacles to produce ciliary feeding current of water III. Collar bears two or more tentaculated arms . IV. one pair of gill –slits or none V. Gonnads are few in numbers. VI. Reproduction by budding. Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College Order A. cephalodiscida I. Solitary or living in a common gelatinous house. II. Two gill-slits are present. III. Single pair of gonads is present. IV. 4 – 6 tentaculated arms are present Ex: cephalodiscus Order B. rhabdopleuara I. Colonial forms II. Gill-slits are present III. Single gonads arepresent IV. Single pair of tentaculated arms. Ex. rhabdopleura Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College Class 3. Planctosphaeroidea I. These are known only by a round transparent pelagic larva related to tornaria larva II. the larva has branching arborescent ciliated bands on the surface III. The alimentary canal of larva is U shaped. IV. The adult form is yet unknown Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College Class 4. Graptolita I. These are extinct colonial hemichordates. II. These are mainly known from the fossil structures of their tubes. III. Each animal is housed in a zooid. IV. These were abundant in the ordovician and silurian period. Ex : Dendrograplus Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College REPRESENTATIYE TYPES 1. Saccoglossus : Saccoglossus is & soft cylindrical, marine and burrowing animal. Body is divisible into proboscis, collar and a trunk. Proboscies or protosome is excep-tionally elongated. Collar slightly over- hangs the beginning of the trunk. Trunk is differentiated into anterior branchial region and posterior branchial region. Genital ridges are abaent. hepatic caeca are not visible. Alimentary canal is straight and anus is present on the posterior end of the body. Sexes are separate and fertilization ia external. Development includes a free-swimming tornaria larva. Saccoglossus is found in the Indo- Pacific Atlantic costs, New Zealand and Australia Fig A Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College Fig A: Saccoglossus Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College 2. Cephalodiscus : Cephalodiscus individuals or zooids occur together in large aggregations attached to objects on the sea bottom in tropical and temperate oceans. The zooids live in separate tubes embedded in a common matrix called a coenecium but the various zooids are free from each other. Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College A zooid of Cephalodiscus has a general structure like that of Balanoglossus. The body has proboscis, collar and trunk borne on a hollow muscular stalk.The proboscis is a ventrally bent disc. The trunk is plump sac having a U shaped alimentary canal with a ventral mouth and dorsal anal. Fertilization and direct development with no larval stage occur in the coenecium. The buds become free and each forms a zooid which secret a tube. Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College 3. Rhabdopleura: Rhabdopleura is a true colonial form. The colonies are Attached to stones, corals and sessile marine animal found in the north Atlantic. Fig: Rhbdopleura (Single Zooid) Circulated by (Paper C3T): Dr. Ranajit Kumar Khalua, Assistant Professor, Narajole Raj College.
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