Phylum - Hemichordata , General Characters , Examples

Defination

• Hemichordates are marine  invertebrate worm like animals.

• This is  phylum which has close  relationship with chordates and Echinodermata.

• Earlier, Hemichordata were considered as chordates but now put in a separate phylum under non chordata.

General characters 

• Hemichordates have a rudimentary structure in collar region called stomochord which is similar to notochord.

• Animals are worm like, marine with organ system level organisation.

• They are bilateral symmetrical, Triploblastic and Coelomate animals.

• Their Animals are cylindrical and body is divided into proboscis, Collar and trunk.

• Circulatory system is open type.

• Respiration takes place by gills.

• Excretion take place by Proboscis glands.

• Saxes are separated. Fertilisation are external. Development is indirect.

Examples of Hemichordata

1. Balanoglossus

• It is also  known as Acorn worm.

• It is deutrostome because anus is developed before mouth.

• It is worm like animals marine animals.

• Body is divided into proboscis, Collar and trunk.

• The alimentary canal is straight starting from mouth and ending with anus.

• It has U shaped paired gills slit.

• Notochord is present on upper part of body without nerve chord.

• Saxes are separated. Fertilisation are external. Development is indirect.

2. Saccoglossus

• It is soft body animals and body is divided into Proboscis collar trunk.

• It is found in spirally coiled burrow in ocean.

• It uses its proboscis to push the body on sand.

• Mouth is located internally at junction of Proboscis and collar.

• The gills are located internally in trunk region.

• It has  Glomerulus in proboscis which filter and release the excretory waste. 

• The egg are converted into tornaria larva which undergo metamorphosis into young animals.