Animals in the same phylum may have different nervous system structures. for example, octopuses have large, complex brains while clams have a simple network

The correct answer will be- ring-like network

Explanation:

Both Octopus and Clams (Bivalves) belongs to the same phylum called Mollusks but different classes.  Although both are molluscs they show variations in their external as well as internal structures.

The case of their nervous system is an example of the nervous system as the nervous system of clams is very simple and consists of ganglia which form a ring-like structure around their oesophagus whereas the nervous system of octopus is very complex just like invertebrates.

Thus, ring-like a network is the correct answer.

search in internet u can get it