Let's start out by defining what each of our answer choices are:
0. A cephalopod - cephalopods are usually any organism that falls under the molluscan class ,Cephalopoda,. Living organisms are usually marine animals such as squids and octopuses.
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1. An arachnid - arachnids fall under "invertebrates" and usually contain jointed legs as their telling physical feature. Living organisms in this class usually are spiders and scorpions.
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2. An invertebrate - invertebrates are organisms that do not have a vertebral column or a backbone for short. Classes that fall under being invertebrate are arthropods and mollusks.
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3. A vertebrate - vertebrates are the opposite of invertebrates; these organisms ,contain, a vertebral column. Examples of living organisms would be a human or an ape.
We are given that a butterfly has a centralized brain, but not a spinal column. That would mean that butterflies would not have a backbone, aka a vertebral column.
Therefore, butterflies will be classified as invertebrate organisms.