PORIFERA-LARVA –PARENCHYMA AND AMPHIBLASTULA LARVA
I Parenchyma Larva is seen in the life history of Leucosolenia. The life history of Leucosolenia was described by Metchnikoff in 1879 and Minchin in 1896.
The fertilisation is internal. Zygote undergoes holoblastic cleavage and develops into coeloblastula. It shows a hollow cavity covered by a single layer of cells.
Many amoeboid cells enter the central cavity and it becomes parenchymuia larva (or) stereogastrula.
This larva shows an outer layer of flagellated cells and a mass of internal amoeboid cells. At the posterior and non-flagellated cells are present called archaeocytes. This larva swims in the water for sometime. Then attaches to a suitable substratum.
The amoeboid ceils from interior will come outside and give dermal layer and mesenchyme. The flagellated cells will surround the inner spongocoel. At its apex an osculum is formed. It grows into adult sponge.
AMPHIBLASTULA LARVA :
Amphiblastula larva is a typical free swimming larva formed in Sycon sponge reproduction.
1. It is ova! in shape.
2. It shows small micromeres with flagella on one side.
3. The other half of the larva shows large macromeres.
4. The larva comes out of the sponge through osculum.
5. It swims in the water for some time with the help of flagella.
Amphiblastula undergoes metamorphosis. The macromeres will overgrow the micromeres and gastruiation takes place. Because of which flagellated cells become internal Then it attaches to a substratum.