All animals, and perhaps all living beings, including those without an identifiable brain, have intelligence, or cognition if you like; are therefore intelligent.
It is not because we are so limited that we do not (yet) understand their intelligence that they would not have it.
Even single-celled organisms exhibit rudimentary intelligent behavior, such as acquiring (through senses), processing, storing, and using information.
Super smart slime
WY – single-celled creatures that live in immense, sticky groups in the oceans – do not speak human languages. But WY do think in at least the eight most spoken human languages. WY observe and WY communicate with each other by splitting and merging. WY may not have computers or internet and humans may think WY are filthy slime without consciousness, but WY have a high group intelligence. WY think, therefore WY are. WY are considering helping the planet and all other living beings to decimate, or perhaps even eradicate, the invasive and destructive species that calls itself HUMAN.