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How many from the following phylum has e...

How many from the following phylum has external fertilisation with indirect development ?
{Porifera, Ctenophora , Echinodermata, Hemichordata }

A

Four

B

Three

C

Two

D

One

Text Solution

AI Generated Solution

The correct Answer is:
To solve the question of how many of the listed phyla have external fertilization with indirect development, we will analyze each phylum one by one. ### Step 1: Analyze Porifera - **Fertilization**: In Porifera (sponges), fertilization is internal. Male gametes enter the sponge body through water currents and fertilize the ovum internally. - **Development**: Since fertilization is internal, we do not consider Porifera for external fertilization with indirect development. ### Step 2: Analyze Ctenophora - **Fertilization**: In Ctenophora (comb jellies), fertilization is external. The eggs and sperm are released into the water column where fertilization occurs. - **Development**: The development in Ctenophora is indirect, meaning they go through a larval stage before reaching adulthood. - **Conclusion**: Ctenophora qualifies as having external fertilization with indirect development. ### Step 3: Analyze Echinodermata - **Fertilization**: In Echinodermata (like starfish), fertilization is also external. The eggs and sperm are released into the water for fertilization. - **Development**: However, Echinodermata exhibit retrogressive development. They start with an indirect larval stage but eventually develop into a direct adult form. Since the development is not strictly indirect throughout, we do not count Echinodermata as fitting the criteria. ### Step 4: Analyze Hemichordata - **Fertilization**: In Hemichordata (like acorn worms), fertilization is external. The eggs and sperm are released into the water. - **Development**: The development in Hemichordata is indirect, involving a larval stage before reaching adulthood. - **Conclusion**: Hemichordata qualifies as having external fertilization with indirect development. ### Final Count After analyzing all four phyla: - Ctenophora: External fertilization with indirect development (1) - Hemichordata: External fertilization with indirect development (2) - Porifera: Internal fertilization (not counted) - Echinodermata: External fertilization but retrogressive development (not counted) Thus, the total number of phyla that have external fertilization with indirect development is **2** (Ctenophora and Hemichordata). ### Answer **2**
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