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Etymology: From the Greek Hemi for half and the Latin Chorda a chord. Characteristics of Hemichordata: 1)Bilaterally symmetrical. 2)Body has more than two. The Hemichordata share some characters, such as pharyngeal gill slits or pores, that have been shown to be homologous with those of chordates. However. The Hemichordata are soft-bodied, worm-like marine organisms which are often The Hemichordata share characteristics with both the Chordata (their name.

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In this article we will discuss about Hemichordata: General Characters of Hemichordata 2. Circulatory system simple and well developed; closed type; usually with a contractile heart vesicle and two longitudinal vessels, one dorsal and one ventral, interconnected by lateral vessels and sinuses.

Development mostly indirect through a free swimming tornaria larva. Direct development is cgaracteristics found in some forms. This class is represented by a few small rounded, transparent and pelagic larvae, supposed to be specialised tornaria of some unknown hemichordate Planctosphaera pelagica.

The larva has branching arborescent ciliated bands on the surface. The alimentary canal of larva is U-shaped. The adult form is yet unknown.

Phylum Hemichordata: Features and Classification

These are extinct colonial hemichordates, mainly known from the fossil structures of their tubes. Each animal is housed in a zooid. These were abundant in the Ordovician and Silurian periods. It is a marine, slender soft-bodied tongue worm living in spirally twisted furrows. Body is divisible into proboscis, collar and a trunk.

Proboscis or protosome is exceptionally elongated and pointed than in other tongue worms. Collar slightly overhangs characteirstics beginning of the trunk covering first three or four pairs of gill- pores.

Introduction to the Hemichordata

Trunk is differentiated into anterior branchial region and posterior branchial region. Genital wings and hepatic caeca are absent. Alimentary canal is straight and anus lies at the posterior end of the body.


Mature gonads are yellow in male and gray in hemichorddata and their position is marked externally by dorsolateral genital folds in the middle part of the trunk.

Synapticula are absent so that tongue bars hang freely in their gill-slits. Sexes are separate and fertilisation is external. Development is direct without a free- swimming tornaria larva. It is soft-bodied, slender marine burrowing animal. The general colour of the animal is yellowish. Its body is elongated and divisible into proboscis, collar and trunk.

Proboscis and collar are short, while trunk is quite elongated. Gonads are situated in the genital wings. Hepatic caeca are distinct. Development is indirect involving a free-swimming tornaria larva. Ptychodera is found in the sea of tropical and subtropical regions. The zooids live in separate hemjchordata embedded in a common matrix called a coenoecium but the various zooids are free from each other.

A zooid of Cephalodiscus has a general structure like that of Balanoglossus. The body has a proboscis, collar and trunk borne on a hollow hemidhordata stalk. The proboscis is a henichordata bent disc.

The collar bears several hollow branched arms in two rows, they bear tentacles and are spoken of as tentaculated arms, the arms bear cilia which drive a food laden current of water into the mouth. The trunk is a plump sac having a U-shaped alimentary canal with a ventral mouth and a dorsal anus. In the anterior part of the trunk is a single pair of gill-clefts.

Sexes are separate, each has a pair of gonads opening by separate gonopores situated dorsally on the front part of the trunk. Fertilisation and direct development with no larval stage occur in the coenecium.

The original individual is produced sexually, on its trunk is a peduncle bearing buds, the buds become free and each forms a zooid which secretes a tube. The colonies are attached to stones, corals, and sessile marine animals mostly in the North Atlantic.


The colony has a thin horizontal branching tube called a coenecium from which short erect tubes arise, each containing a zooid. A zooid is minute, its general structure is like an enteropneust with a proboscis, collar and trunk, attached to the trunk is a stalk. On the collar is a pair of hollow branching arms having cilia which collect the food of the animal. Alimentary canal is U-shaped so that the anus lies close to the mouth.

There are no gill-clefts and a glomerulus is lacking. Sexes are separate, each sex has a single gonad with a gonopore hemidhordata the right side. Large yolky eggs are laid.

An original individual is produced sexually, on its trunk is a peduncle which bears characferistics, the buds do not become free and each forms a zooid. Each zooid secretes its own ringed vertical tube or case which hemichofdata formed ring by ring. The horizontal part of each tube has a black stolon which connects the various zooids to the parent so that a colony of connected zooids is formed.

ZoologyInvertebrate ZoologyHemichordata. Habitat, Development and Affinities. History, Characters and Classification. This is a question and answer forum for students, teachers and general visitors for exchanging articles, answers and notes.

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