Hemichordates are a group that has a combination of both invertebrate (Echinoderm) and chordate characteristics.
The hemichordates along with Echinoderms and chordates belong to the group deuterostome branch of animal kingdom.
Because of their close relationship to chordates these animals are called pre-chordates. The common examples of this phylum are Balanoglossus and saccoglossus.
General Characters
Soft bodied worm-like animals.
Body is divided into an anterior proboscis. Collar and trunk.
Body wall is made of unicellular epidermis with mucus-secreting cells.
Digestive tract is straight and may show variations.
Coelomic cavities correspond to each of the three body regions i.e. that of proboscis, collar and trunk coelomic pouches.
Circulatory system consists of a median dorsal and a median ventral vessel.
Respiratory system is composed of Gill-slits forming a dorsal row behind collar.
Excretory system has single glomerulus connected to blood vessels.
Nervous system has a sub-epidermal plexus of cells and fibres.
Balanoglossus and Saccoglossus