discuss the characters and affinities of amphioxus
Answers
Answer:
In this article we will discuss about the characters and affinities of Branchiostoma.
Characters of Branchiostoma:
General Characters of Branchiostoma:
1. Marine, widely distributed in shallow waters.
ADVERTISEMENTS:
. Mostly sedentary and buried with only anterior body end, projecting above bottom sand.
3. Body small, 5 to 8 cm long, slender, fish-like, segmented and transparent.
4. Body has trunk and tail. Head lacking.
5. Paired appendages lacking. Median fins present.
Explanation:
. Exoskeleton absent. Epidermis single-layered.
7. Muscles dorso-lateral, segmented into myotomes.
8. Coelom enterocoelous, reduced in the pharyngeal region by development of atrial cavity.
9. Notochord rod-like, persistent, extending from rostrum to tail, hence, the name Cephalochordata.
10. Digestive tract complete. Pharynx large, perforated by numerous persistent gill-slits opening into atrium.
11. Respiration through general body surface. Special organs for respiration absent.
12. Circulatory system well developed, closed without heart and respiratory pigment. Hepatic portal system developed.
13. Excretion by protonephridia with solenocytes.
14. Nerve cord dorsal, tubular without ganglia and brain. Dorsal and ventral nerve roots separate.
15. Sexes separate. About 25 pairs of gonads. Gonoducts lacking. No asexual reproduction.
16. Fertilisation external in sea water.
17. Development indirect, including a free-swimming larva.
18. Cephalochordata has about 30 species of the genus Branchiostoma and all put in the class Leptocardii.
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