Balfour classified urochordata, cephalochordata and vertebrata as phylum chordata. But Bateson included Hemichordata in this phylum chordata. These members are considered as primitive chordata.
- The body of these animals is long and worm like.
- These are marine animals. They make burrows in the coastal sandy shores.
- Their body is divisible into proboscis, collar and trunk.
- They emit strong idoform smell.
- Their body is covered by ciliated epidermis.
- Their body wall is muscular.
- They show enterocoeliccofelome. This coelome is divided into 5 cavities, one in the proboscis, two in the collar and two in the trunk region.
- In the proboscis buccal diverticulum is present. It is called stctnochord. It is comparable to notochord.
- In these animals excretory organs are absent. In the proboscis glomerulus is present. It will help in excretion.
- Digestive system is well developed. The alimentary canal is long. It starts with mouth and ends with anus. Pharynx is useful for food collection and respiration. These are filter feeders.
- On the lateral sides of Pharynx gill slits are present.
- Blood vascular system resembles annelids, blood vascular system more.
- Heart and Pericardium are present in the proboscis.
- In the collar lateral blood vessels are present.
- Nervous system includes a dorsal tubular nerve cord and solid ventral nerve cord.
- These animals will not show brain and cranium. Hence this is grouped aeraniata.
- These are unisexual animals gonads will give gonoducts.
- Fertilization is external.
- Holoblastic clevage is seen.
- In the life history a larval form is seen. Tornaria larva is usually seen.
Hemichordata subphyllum is classified into two classes.
Class 1: Enteropneusta:
- These animals are worm like and cylindrical.
- They are burrowing animals.
- They show many pairs of gills.
- Alimentary canal is long and straight. Ex: Balanoglossus, Ptychodera.
Class 2: Pterobranchia:
- They lead sedentary life.
- They are tubicolous.
- They are colonial organisms.
- They show less number of gills.
- Alimentary canal is 'U' shaped. Ex: 1. Cephalodiscus 2. Rhabdopleura.