Evolutionary Development in Sponges

Sponges are considered the simplest of the multicellular animals and belong to the phylum Porifera. They are a group of filter-feeding marine animals that lack any true tissues or organs. Sponges are sessile and attach themselves to solid substrates such as rocks, coral reefs, and shells. They have a unique body plan, which consists of a porous body with many channels that allow water to flow through them.

Multicellularity in Sponges

The evolution of multicellularity is considered a significant event in the history of life on Earth. It allowed for the development of more complex organisms with specialized cells and tissues. Sponges are believed to be the first animals to evolve multicellularity. They are composed of a loose aggregation of cells that are held together by a gel-like matrix called mesohyl. This mesohyl contains various types of cells, including choanocytes, which are responsible for filtering food particles from the water, and amoebocytes, which are involved in digestion, reproduction, and other functions.

Sponges lack true tissues, organs, and a nervous system, but they exhibit a high degree of cellular differentiation and specialization. They have various cell types that are involved in different functions, such as feeding, reproduction, and defense. Some sponges also have specialized cells called sclerocytes that produce spicules, which are small, needle-like structures that provide support and protection.

Conclusion

In conclusion, sponges are considered the simplest multicellular animals and are believed to be the first animals to evolve multicellularity. They lack true tissues and organs but exhibit a high degree of cellular differentiation and specialization. Sponges have a unique body plan and play an important role in marine ecosystems as filter feeders and habitat providers for other marine organisms.

D is correct option because sponges have ...
- no digestive system...
- no tissue only cellular level of organisation ..
- and they are also assymetrical ...

but they are multicellular ...
so multicellularity is a key evolutionary development seen first in sponges...