In coelentrates fertilization is mainly external ,may be internal in few species.i.e. hydra. developement is indirect with larval stages.
In annelids, the fertilisation may be internal or external & developement is direct or indirect.

Fertilisation and Development in Coelenterates and Annelids

Fertilisation in Coelenterates

Coelenterates are a group of aquatic animals that include jellyfish, coral, and hydra. They are known to reproduce both sexually and asexually.

- Internal or External Fertilisation: Coelenterates can undergo both internal and external fertilisation. In internal fertilisation, the male releases sperm into the female's body, where it fertilises the eggs. In external fertilisation, both the male and female release their gametes into the water, where fertilisation occurs.

- Development: In coelenterates, the development can be either direct or indirect. In direct development, the embryo develops into a juvenile form that closely resembles the adult form without undergoing any metamorphosis. In indirect development, the embryo develops into a free-swimming larval stage, which then undergoes metamorphosis to become the adult form.

Fertilisation in Annelids

Annelids are a group of segmented worms that live in a wide range of habitats, including marine, freshwater, and terrestrial environments.

- Internal or External Fertilisation: Annelids undergo internal fertilisation, which means that the male deposits sperm directly into the female's body, where it fertilises the eggs.

- Development: In annelids, the development can be either direct or indirect. In direct development, the embryo develops into a juvenile form that closely resembles the adult form without undergoing any metamorphosis. In indirect development, the embryo develops into a free-swimming larval stage, which then undergoes metamorphosis to become the adult form.

Conclusion

Coelenterates can undergo both internal and external fertilisation, whereas annelids only undergo internal fertilisation. In terms of development, both coelenterates and annelids can have either direct or indirect development.