1. Hemichordates were earlier treated as a subphylum of Chordata (or Prochordata).
2. They are now viewed to be an independent phylum of invertebrates, close to Echinodermata.
3. The animals of this group possess the characters of invertebrates as well as chordates.
4. This phylum consists of a small group of wormlike, so marine animals, mostly tubiculous and commonly called the 'acorn worms' or 'tongue worms'.
5. They are bilaterally symmetrical, triploblastic and coelomate animals with organ system level of organisation.
6. Body : cylindrical and is divided into three regions,
I. the anterior proboscis,
II. a short collar and
III. a long trunk.
7. Most they are ciliary feeders.
8. Circulatory system is simple and open or lacune type with a dorsal heart.
9. Respiration is through paired gill slits opening into the pharynx.
10.Excretion - Single proboscis gland or glomerulus situated in the proboscis.
11.Nervous system - primitive.
12.Sexes are separate and exhibit sexual mode of reproduction; Fertilization is external.
13.Development is indirect with a free swimming tornaria larva. Eg:Balanoglossus, Saccoglossus.
