The word Cephalochordata is formed from the Greek word Kephale meaning head and chorda meaning chord. They are commonly called lancelets. First they are described as Amphioxus (amphi = both means both ends, ends = oxys means sharp). Later, according to the law of precedence, they were named Branchiostomata (branchia = gill, stoma = mouth). Cephalochordates are called invertebrate chordates. In 1774 scientist Peter Simon Pallas (1774) described Branchiostoma lanceolatum. Their number of species is 33.
Characteristics of Cephalochordata
1. Body long, slender, laterally compressed, transparent, boat-shaped and pointed at both ends.
2. Anterior to the body is an oral hood and oral cirri.
3. From the front to the back of the body there is a permanent notochord and nerve cord.
4. The pharynx has numerous gill openings. The gills open into the atrium.
5. At the tip of the body are atriopores.
6. The body is 3-7 cm long and has 60 pairs of myotome muscles on both sides of the body.
7. They look a lot like Ballam Aga. That is why they are nicknamed Bhallaka animals.
8. Their pharynx contains numerous atria and atriopores.
9. They are excreted.
10. They are called lancelets in English.
11. They do not have a clear head.
12. The circulatory system is closed and developed. Hepatic portal system is present.
13. The main excretory organ is protonephridia. Protonephridia contain solenocytes cells.
[KEY WORDS TO REMEMBER CHARACTERISTICS: boat, oral hood, oral cirri, notochord, nerve cord, pharynx, myotome muscle, excreta, lanceolate, protonephridia]
Some animals of Cephalochordata
Branchiostoma lanceolatum (Amphioxus)
Branchiostoma belcheri
Branchiostoma floridae
Asymmetron inferum.