Lobsters

[crgb14]

Is it true that if all animals were the same size then lobsters would have the smallest brains??

[brachiopod]

No.

There are single celled animals that don't have a 'brain'.

Also cnidarians (anemones, corals, and jellyfish), poriferans (sponges), and bryozoans ('polyps') are all animals with considerably less defined brains than lobsters.

Although the lobster 'brain' (if it can be called that) is small, it is just one of a number of connected 'nerve bundles' or ganglia along the length of its body.