Can You Explain The Affinities Of Amphioxus With Hemichordata And Urochrodata?


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saima jabeen answered
Affinities with Hemichordata:
Amphioxus resemble with hemichordates in having similar:
1. Pharyngeal apparatus with numerous gill slits and gill bars.
2. Filter feeding mechanism.
3. Respiratory mechanism.
4. Entrocoelic coleom.
5. Numerous gonads without gonoducts.
Muscles I Hemichordata are unsegmented, nervous system distinctly of non-chordate type, gill slits dorsal in position instead of lateral and a postnatal tail is lacking.

Affinities with Urochordates:
Amphioxus resemble with Herdmania (a urochorate) in many respect:

1. Primitive ciliary feeding and respiratory mechanism.
2. Large pharynx having numerous lateral gill slits, epiphyrangeal groove, endostyle and periphyrangeal bands.
3. Atrium opening to the outside through atripore.
4. Identical cleavage and gasrtulation.
5. Presence of notochord, dorsal hollow nerve chord and postnatal tail n larva of urochordates.
The adult urochordates differ from Amphioxus in many characters such as: body segmented; covered by a test made of cellulose; without notochord and hollow nerve chord; without nephridia; having a liver and a muscular heart. It means both the group has common ancestors but Amphioxus is better evolved than urochordates.

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