Classification Of Protochordates : Classification Of Protochordates Protochordata Hemichordate Urochordatea Cephalochordate (Half-chordates) (Tail-cord) (Head-cord) Protons means first and chordae means cord also called as Acraniata as cranium is absent
General Characters Of Protochordata: General Characters Of Protochordata They are marine, small & primitive chordates Live singly & Feed on microbes or particulate matter Head, Skull & Cranium are absent Body covered by single transparent layer called Tunic. The body cavity is enterocoelic. They are jaw less animal. Pharynx with pharyngeal gill slits. Circulatory system includes blood without erythrocytes, heart , vessels and sinuses. Body bears protonephoric kidney. Nervous system is primitive . Sexes are separated or hermaphrodite. Development indirect with larval stage.
General Characters Of Hemichordate: General Characters Of Hemichordate Solitary or colonial mostly marine tubicolous, soft and fragile animal Body is divided in to 3 regions proboscis, collar and trunk. Soft bodied, vermiform, triploblastic, bilaterally symmetrical unsegmented animal. Body wall with single layered epidermis lower layer dermis is absent. Body cavity is true coelom, divided into 3 parts i.e. protocols, mesocoel and matacoel Complete digestive tract straight with terminal anus os ‘U’ shaped with anus nearer to mouth. Gill slits are present or absent if present then number varies. Buccal diverticulum wrongly named as notochord, is present. Closed circulatory system is present. Blood is colorless without blood cell. Excretory system consist of the glomerulus and a proboscis gland lies in proboscis. Nervous system is primitive consist of intra-epidermal nerve plexus. Reproduction is sexual: sexes are separated or hermaphrodite. Gonids one or many pairs. Fertilization is external. Development may be direct or indirect with a Torn aria larva. They feed on micro-organism and debris by cilary mechanism. There are about 70 species. Ex.- Balanoglossus, Cephalodiscus, Saccoglossus etc.
General Characters Of Urochordatea:
General Characters Of Urochordatea All are exclusively marine and occur in all the seas at level of 5 km depths from surface water. They are either solitary or colonial. Majority of them are sedentary few are free swimming and pelagic. They possesses the ability of de- differantiation (grow small during starvation and develop again on normalization of condition) Body covered with cuticular tunic or test in adult. Body without head varies in size, form, Colour. Notochord present in tail of larva and not in adult. Body divided in to trunk and tail without appendages. There is no coelom. Alimentary canal is complete with large pharynx perforated by two or numerous gill silts for respiration. (Perforated -dotted with small holes) Circulatory system is open type with ventral heart. Excretion is carried out by nephrocytes cell pyloric or neural
gland. They are hermaphrodite ,fertilization is external . Asexual reproduction by budding is common. Development include a minute free swimming tadpole larva with tail with dorsal nerve cord notochord restricted to tail region only. About 2200 Urochordatea are known Ex. Hard mania, doliolum, ascidia etc.
General Characters Of Cephalochordate: General Characters Of Cephalochordate They are exclusively marine and show a burrowing life in shallow seas. Body is fish like adapted for burrowing and swimming. Body is without head but tail is present. There is no paired appendages but median pins i.e. dorsal caudal and ventral fins are present. Notochord runs through the length of body and extended beyond the nervous system to the tip of the snout. A true enterocoetous coelom is present. Alimentary canal is complete. It is cilliary feeder. Respiration occur by diffusion through general body surface. Circulatory system is closed respiratory pigment and heart are waiting. Hepatic portal system is development. Protonephredia with solanocytes. Sense organs are absent. Dorsotubular nerve cord without brain and ganglia. Two cerebral and several pairs of spinal nerves are present. Sexes are separated and gonads without gonoduct. Fertilization is external. Cleavage is hologiastic, development is indirect including free swimming ciliated larva Ex.- Amphioxus
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