Amphioxus also resembles with other many vertebrates in many respects:
1. Metamerically arrange mytomes.
2. True coelom lined by mesodermal epithelium.
3. Postnatal tail
4. Midgut diverticulum comparable with liver.
5. Well-formed hepatic portal system.
6. Similar arrangement of main longitudinal vessels with forward flow of blood in ventral and backward flow in dorsal blood vessel.
Objections:
Amphioxus varies from jawless fishes and other vertebrates in most of their primitive features such as:
1. Lack of head, paired limbs, skull, vertebral column, muscular heart, red blood corpuscles, brain, specialized sense organs, gonoducts etc.
2. In possessing nephridia, atrium, numerous gonads, asymmetry etc.
Conclusion:
In 1834, Costa considered Amphioxus to be a vertebrate and named it Branchiostomum lanceolatum. In 1836, Yarely placed it in the lower vertebrate group and named it as Amphioxus. In 1880 Balfour placed the Amphioxus along with the tunicates and vertebrates in the phylum chordate. Amphioxus has nervous system, blood vascular system, digestive system developed on the vertebrates pattern. The presence of notochord hollow dorsal nervous system, gill slits in larval and adult stages shows resemblance to the chordates.
1. Metamerically arrange mytomes.
2. True coelom lined by mesodermal epithelium.
3. Postnatal tail
4. Midgut diverticulum comparable with liver.
5. Well-formed hepatic portal system.
6. Similar arrangement of main longitudinal vessels with forward flow of blood in ventral and backward flow in dorsal blood vessel.
Objections:
Amphioxus varies from jawless fishes and other vertebrates in most of their primitive features such as:
1. Lack of head, paired limbs, skull, vertebral column, muscular heart, red blood corpuscles, brain, specialized sense organs, gonoducts etc.
2. In possessing nephridia, atrium, numerous gonads, asymmetry etc.
Conclusion:
In 1834, Costa considered Amphioxus to be a vertebrate and named it Branchiostomum lanceolatum. In 1836, Yarely placed it in the lower vertebrate group and named it as Amphioxus. In 1880 Balfour placed the Amphioxus along with the tunicates and vertebrates in the phylum chordate. Amphioxus has nervous system, blood vascular system, digestive system developed on the vertebrates pattern. The presence of notochord hollow dorsal nervous system, gill slits in larval and adult stages shows resemblance to the chordates.
