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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Kinorhyncha mud dragons Priapulida penis worms. The proboscis is modified into into a shield which secretes the collagenous burrow in those species that live in one. They have a diverticulum of the foregut called a stomochordpreviously thought to be related to the chordate notochordbut this is most likely the result of convergent evolution hemuchordata than a homology.

Hemichordata: Characters and Classification (With Diagram)

Phyllograptus typus Graptolite Ordovician Victoria, Australia. In the collar their are giant nerve fibres, but their function is poorly understood and the animal can survive reasonable well without them.

Sexes are separate, each has a pair hemichorsata gonads opening by separate gonopores situated dorsally on the front part of the trunk. Evolution of the chordate body plan: Acorn worms are solitary worm-shaped organisms.

They have a wide distribution and can be found in most of the worlds waters both in shallow coastal waters and in the deeper seas. The graptolite colony consisted of one or many branches that were straight, curved or spiral.


Proboscis and collar are short, while trunk is quite elongated. Their burrows may have several openings at one end. Filter feeders have mucous secreting glands and numerous cilia on their proboscis. The phylum is divided into two classes, the Pterobranchia and the Enteropneusta.

Thus these marine worms are of great interest for the study of the origins of chordate development. This stalk is used for support in some species, but is joined at its farther end to a common stolon in colonial species.

The alimentary canal of larva is U-shaped. The internal relationships within the hemichordates are shown below.

Hemichordata: Characters and Classification (With Diagram)

The trunk is a plump sac having a U-shaped alimentary canal with a ventral mouth and a dorsal anus. The colony has a thin horizontal branching tube called a coenecium from which short erect tubes arise, each containing a hemidhordata.

Graptolite fossils appear from the Cambrian and dissapear in the Carboniferous. The two classes share some attributes but are quite different in others. Behind the mouth is a buccal cavity which hemichoreata into a pharynx which possess gill slits.

Tree of Life Hemichordata. A third class, Planctosphaeroidea, is known only from the larva of a single species, Planctosphaera pelagica. Development is indirect involving a free-swimming tornaria larva. The enteropneusts have two developmental strategies: By using this characterisstics, you agree to the Terms of Charactwristics and Privacy Policy.

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. Hemichordates are classically known to develop in two ways, both directly and indirectly.


Gonads are situated in the genital wings.

Hemichordate – Wikipedia

Feeding is either filter feeding or substrate eating. The fourth division occurs mainly in blastomeres in the animal pole, which divide transversally as well as equally to make eight blastomeres. Synapticula are absent so that tongue bars hang freely in their gill-slits. These gill slits are believed to be used primarily to assist gaseous exchange respiration. Gaseous exchange occurs over the whole body as well as in the pharyngeal slits.

Oligometric body, underlying a tricoelo-mate organization, and comprising of a large pro-somal proboscis, a small meso- somal collar and a large, elongated or sac-like metasomal trunk. Yannanozoon lividum from the early Cambrian Chengjiang Biota is a putative, primitive hemichordate, though some scientists have assigned it to the enigmatic phylum Vetulicolia. Aspidograptus smithonensis Cbaracteristics cambrian Tasmania, Australia.


For this the hemichordates have been included among the non-chordates as a separate phylum. Genital wings and hepatic caeca are absent. Each animal is housed in a zooid. The pharyngeal wall is perforated by 1 to more than pairs of slits through which water flows out.

Proboscis or protosome is exceptionally elongated and pointed than in other tongue worms. Alimentary canal is U-shaped so that the anus lies close to the mouth.