The ripples and folds of the brain are the source of all of our actions, emotions and instincts. While you may know what a human brain looks like, animal brains come in a variety of shapes and sizes. Still, no matter what they look like, all brains are made up of a grouping of nerve cells and act as the coordinating centre for sensation and actions.

Does Size Really Matter?

While size is loosely linked to brain function, a large brain does not necessarily correspond to a higher level of intelligence. The more important factor for approximating intelligence is how much of the body the brain takes up, or our brain-to-body mass ratio. We can see the brain and body mass of some animals displayed in the graph below. The species above the trend line have higher brain-to-body mass ratios, and are typically thought to be more intelligent than the species with smaller ratios below the line.

Amazing Brain Anatomy

There are countless different designs for animal brains; these are some of the champion species for having the most unusual brains out there:

Spider Brains

Spiders have very large brains for their size, some spiders having brains that take up 80% of their body. Spider brains can also take on very interesting shapes, existing not only in the spiders head, but spilling into other body cavities and legs. These large brains are important for spiders for executing activities like web building or hunting.

Sea Squirt Brains

Sea squirt larvae start developing a small brain like many other organisms, as well as a primitive spine and eye. The larvae swims around like a tadpole until it finds the place where it will spend the rest of its life and attaches itself head first to the sea floor. The sea squirt will then absorb its spine, eye and small brain (it no longer requires them) effectively eating its own brain. It can use this body material to develop its stomach and will spend the rest of its life anchored to this location.

Squid Brains

The doughnut shaped brain of the squid is very effective for linking information between their two large eyes, however this structure limits the squid in a peculiar way. The squid’s esophagus runs through its centre, so everything the squid eats must pass through its brain. If the squid consumes prey that is too large, it risks critically damaging its brain tissue.



Koala Brains

Koalas are known for being sleepy and lazy, which is likely due to a nutrition-poor diet of otherwise toxic eucalyptus leaves. Lucky for them though, a koala also has a relatively small brain to body ratio than that of other marsupials, which means that their brains won’t burn up too much of what little energy they do have. Their brains only take up 61% of their brain cavity and it is pressed against the inside surface by cerebrospinal fluid.

The amazing thing about a koala brain, besides the small size, is that it is relatively smooth! Smooth brains are called “lissencephalic” and it isn’t uncommon for a primitive animal like Koalas; koala-like animals date back 25-40 million years. It does, however, contribute to a Koala’s reputation for being a bit dim witted.

Sponge Brains

Almost all animals have a brain, but there are a few exceptions. There is one organism that has no brain or nervous tissue of any kind: the sponge. Sponges are simple animals, surviving on the sea floor by taking nutrients into their porous bodies. There are conflicting theories as to whether or not sponges have always been this way or evolved to get rid of their brain to be more energy efficient.

How do brains work?

Research has shown how nerve cells function, passing electrical and chemical information at speeds up to 400 kilometres per hour. The scientific community has a good understanding of how these brain cells, or neurons, function on an individual level, passing signals from one neuron to the next. The big picture, however, is a mystery we haven’t fully solved yet—deciphering how these neurons coordinate by the millions to receive and send information simultaneously and linking all the body’s systems and organs to function as one unit. So, if you have brains on the brain, maybe neurological research is for you! There are countless mysteries in the animal brain just waiting to be solved.



Still hungry for brains?

Read Bizzarre Brains Part 2: Mind Hijackers. You won't be disappointed.