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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For a more detailed explanation of the different ToL page types, have a look at the Structure of the Tree of Life page. In the genus Cephalodiscusasexually produced individuals stay attached to the contractile stalk of the parent individual until completing their development.

Development is direct without a free- swimming tornaria larva. The most prevalent Hemichordate fossils are the Graptolites which were colonial animals that are primarily known from the upper Cambrian through the Lower Carboniferous Mississippian of the Paleozoic.

Note that images and other media featured on this page are each governed by their own license, and they may or may not be available for reuse. These arms possess a double row of smaller ciliated tentacles. It is forced through the animal’s few vessels by the beating of a muscular heart that forces blood through the central sinus. Behind this is a ‘trunk’ which contains the digestive and reproductive organs. Fertilisation and direct development with no larval stage occur in the coenecium.

The pterobranchs are sedentary, tube-dwelling animals having a short body measuring about mm in length. Development mostly indirect through a free swimming tornaria larva.


Phylum Hemichordata: Features and Classification

There are three classes of Hemichordates. The protosome is followed by a ‘collar’ which bears tentacles in the Pterobranchia but not in the Enteropneusta. They are all marine worm-like animals. The smallest species are only a few millimetres long and the largest, Balanoglossus gigas can reach lengths of 1. The females extrude egg masses onto the surface of the substrate from within their hemichodrata 2, to 3, eggs at a time.

Hemichordata: Characters and Classification (With Diagram)

All known species feed on small particles of organic matter either as filter feeders of as substrate eaters. Hemichordata are divided into two classes: Proboscis or protosome is exceptionally elongated and pointed than in other tongue worms.

In other projects Wikimedia Commons Wikispecies. There are only about 90 known species all of which are benthic, living on the sea floor in their adult form. The animal mesomeres of P. Pterobranchs live in much deeper water than the Enteropneusts, this and their soft bodies means that characteristocs are difficult to study and much less is known about their ecology.

From Wikipedia, the free encyclopedia. These gill slits are believed to be used primarily to assist gaseous exchange respiration. The colonies are attached to stones, corals, and sessile marine animals mostly in the North Atlantic. Cycliophora Symbion Annelida ringed worms. With only between 10 and 20 species the Pterobranchia make up less than one fifth of the Hemichordates. Placozoa Trichoplax Cnidaria jellyfish and relatives.

Alimentary canal is U-shaped so that the anus lies close to the mouth. Filter feeders have mucous secreting glands and numerous cilia on their proboscis.


Large yolky eggs are laid. Most people are unfamiliar with the animals within Phylum Hemichordata, which is small and contains but a few hundred species. The individual animals lived within structures along the length of a hcaracteristics exoskeleton formed from collagen. The Pterobranchia are also extant and form a small and obscure group that characteriztics colonies in which the individuals are interconnected by stems, or stolons made from collagen protein.

Pterobranchia may be derived from within Enteropneusta, making Enteropneusta paraphyletic. Hemichordata Bateson They seldom leave their burrows. The truck ends in a contractile, can lengthen or shorten prehensile can grip like a monkeys tail stalk.

The phylum is divided into two chaaracteristics, the Pterobranchia and the Enteropneusta. Development is indirect involving a free-swimming tornaria larva. Much of the genetic work done on hemichordates has been done to make comparison with chordates, so many of the genetic markers identified in this group are also found in chordates or are homologous to chordates in some way.

Their burrows may have several openings at one end. The Enteropneusta are the acorn worms that remain extant.

The Phylum Hemichordata

The Pharynx leads into an oesophagus which in turn leads to an intestine which is the main site of digestion. Pages in Microscopic Anatomy of Hemuchordata, Vol. This page is a Tree of Life Branch Page.