All about non - vertebrate chordate
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All about non - vertebrate chordate

All about non - vertebrate chordate

The phylum Chordata is broken down into three subphyla such as, Urochordata, Cephalochordata, and Vertebrata. Urochordata and Cephalochordata usually known as non-vertebrate chordates hence they have a notochord, a dorsal nerve chord, a post-anal tail, and pharyngeal gill slits as all invertebrate chordates but don’t have a vertebral column. Invertebrate chordates are coelomates or animals with a true body cavity.

 

In addition, Invertebrate chordates in the phylum Urochordata  also known as Tunicata. There are three main classes in phylum Urochordata such as, Ascidiacea, Thaliacea, and Larvacea.

 

 

The majority of tunicate species are ascidians. They have between 2,000 and 3,000 species.  These animals are sessile. They usually live in marine shallow water. Ascidians live as colonies or solitary. Their body is entirely enclosed in a semi – transparent, sac like test. This sac-like body is encased in a material composed of protein and a carbohydrate compound similar to cellulose. Basel end of the test is thickened and roughened to form a hold fast. This hold fast is used to attach to the substrate. The other end has two arms with two openings while making U shaped body. Those two openings are called siphons which take in water into the body - buccal siphon and push out waste and water - atrial siphon. They are suspension feeders with specialized external coverings for food filtration. Within their body wall, there is a large cavity or atrium containing a large pharynx. The pharynx is a muscular tube that leads to the gut Food particals are filtered through the pharynx and move them to the digestive tract.

 

 

The Tunicata class Thaliacea includes doliolids, salps, and pyrosomes. Doliolids are free living marine animals which can live in both tropical and subtropical seas. They are very tiny animals measuring 1-2 cm in length with transparent, barrel shaped body. Body wall contain series of characteristics 8 muscles bands. Locomotion is done by moving theses muscle bands. They usually move by jet propulsion mechanism. Doliolids have two wide siphons, one located at the front end and the other at the back end. They feed on unicellular organism. Also they act as initial link of marine food webs.

 

 

Cephalochordates represent a small chordate subphylum with around 32 species. These tiny invertebrates resemble fish and can be found living in the sands in shallow tropical and temperate marine waters. The name cephalochordate is derived from the fact that the notochord extends well into the head. Lancelets are filter feeders which body is long few cm. They filter food from the water as it passes through their gill slits in open mouths by ciliary pumping.

 

 

 

 

 

 

 

 

by Nuwandara Mudalige

Photo source : Internet

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