Cephalochordata - Lancelets and Their Unique Characteristics
Cephalochordata, commonly known as lancelets, are marine organisms with a small, fish-like, translucent body. They exhibit typical chordate characteristics such as a notochord, gill slits, and a dorsal nerve cord. Despite the absence of a skull, they are called Acrania. These creatures have notochords and nerve cords that persist throughout life. They lack paired fins but have median fins and thick, segmented muscles. Cephalochordata feature atrium-surrounded pharynx, with gill slits, proto-nephridia, and gonads opening into it. Notable features include the presence of an endostyle and segmented protonephridia for excretion. Reproduction involves external fertilization and indirect development with free-swimming larvae. Examples include Branchiostoma (Amphioxus) and Asymmetron.
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Presentation Transcript
Cepalochordata General characters
1. Looks like Lance eel,hence named as lancelets 2. marine forms 3. body is small, fish like and translucent 4.Typical chordates,like notochord,gillslits and a dorsal tubular nerve chord are present 5.skull is abesent,hence they are called as Acrania
6.Notochord &nerve cord present throughout life and persist in the adult 7.Median fins are present. paired fins are absent 8.dorsolateral muscles are thick and segmented into myotomes 9.Notochord extends from posterior end to anterior end of the body ,beyond the nerve cord. Hence the name Cephalochordata
10.Pharynx is surrounded by atrium which opens out by atrial aperture 11.gillslits ,proto nephridia and gonads open into atrium 12.Endostyle is present on the ventral wall of the pharynx 13.respiratory organs are absent respiration by diffusion 14.circulatory system is closed type 15.Heart,blood cells and respiratory pigment are absent
16.Oral hood ,wheel organ are the characteristic features. Ciliary feeders. Alimentary canal is straight& hepatic diverticulam is present. 17. excretion by paired segmented protonephridia 18.Brain and sense organs are absent 19.sexs are separate 20.many pairs of segmented gonads present
21. Gonoducts are absent 22.fertilisation is external 23.development is indirect and Includes a free swimming larve which exhibits progressive metamarphosis. ex:1.Branchiostoma(Amphioxus) 2.Asymmetron.
