Did you know that some animals can be see-through? The Glass Frog, Ghost Shrimp, European Eel, Jellyfish, and Crocodile Icefish have transparent bodies. Some are completely transparent, while others have organs that you can see from the outside.
So, why are they see-through? How can an animal be transparent? How does this help them in their environments?
Transparency is an adaptation to low-light environments that some creatures have developed over time. These remarkable creatures use their see-through bodies for camouflage and subterfuge.
There are over 160 species of glass frogs living in the tropical regions of Central and South America. They are small frogs, only growing to a maximum of about 3 inches long. Their habitat is mostly in tropical lowland forests and mid-elevation mountain forests.
Not all glass frog species are translucent, but the ones who are, use this trait for camouflage. Glass frogs have see-through bellies, chests, and occasionally sides. If you were to see a Glass Frog from above, it would look light green. But, this coloration can change in gradient. This is because of an effect called edge diffusion. Edge diffusion is when the outline of something becomes hard to see against a similar colored background.
Scientists believe that the glass frog’s translucent skin works to confuse predators and to help the frog blend into its setting.
These transparent animals are closely related to crabs. Four species of Ghost Shrimp have been identified. These crustaceans can be found in freshwaters in the southern United States and as far west as Texas and California. They are bottom feeders that help decompose and enrich the sediment.
Ghost shrimp are often used as bait by fishermen. They can also be kept as pets in an aquarium. They use their transparency for camouflage because they are a favorite treat of many birds and fish. They only come out at night to eat plankton and hide in vegetation by day.
A fully grown European Eel looks like other species of eel. It has an elongated body and one pair of pectoral fins. But, this creature undergoes a unique life cycle and migration that makes it unique.
European eels lay their eggs in the Sargasso Sea. When the eels hatch, they are transparent, leaf-shaped larvae. They ride the Gulf Stream across the Atlantic Ocean, drifting 4,000 miles to the shores of Europe and North Africa. This journey takes about 2 years.
As they move through the Atlantic, they metamorphose into see-through miniatures of their adult form. At this stage, they are called glass eels. They lack color-producing cells, which help to protect the developing eel as it journeys through open waters.
Once it reaches Europe, this eel begins migrating into freshwater streams. They start to darken in color as they travel further. Then, they live in these freshwater habitats where their bodies change to yellow. They can stay in this stage for more than 20 years.
When it is time to spawn, European eels change color again, this time to silver. They travel the long distance back to the Sargasso Sea, where the process begins again.
Unfortunately, in recent years, European eels have been classified as critically endangered. Part of the cause is that they are often used to make food like eel pies and jellied eels. So, a combination of overfishing, pollution, and loss of habitat has made these creatures rapidly decline over the last 40 or so years.
Jellyfish are invertebrate marine animals. There are around 200 known species of these creatures. They can vary in color, shape, and size. The Crystal Jellyfish is nearly completely see-through. It lives in the Pacific Ocean from southern California to Vancouver. They can grow up to 10 inches in diameter and have over 150 tentacles. The Crystal Jellyfish live in open waters feeding on plankton and other jellyfish.
The reason for their near transparency is that they live in deep waters where light does not penetrate. Without teeth, these creatures need invisibility to protect them from predators. Their near-transparent bodies make them hard to spot in the darkness of the ocean.
However, these nearly see-through creatures are also bioluminescent, which means they emit their light. They possess the Green Fluorescent Protein, which produces a bright green light when it is exposed to lights in the blue to ultraviolet range. If they are messed with, they will glow green-blue around their outer bell. This is often used to confuse predators as they escape.
The combination of their transparency and bioluminescence helps them to evade predators.
The Crocodile Icefish was first written about in 1928, when it was caught off the coast of Bouver Island, Antarctica. The fish was described by biologist Ditlef Rustad as a “scaleless and eerily pale” fish. Some parts of its body were pure white, others translucent. It had a long tooth snout and large eyes with quills producing a fan along its back.
Icefish are the only known vertebrates that don’t have red blood cells. These creatures are clear-blooded. Scientists recently theorized that this was an accidental genetic mishap. Red blood cells are responsible for carrying oxygen throughout the body and to the brain. Without these cells, icefish had to alter their entire bodies to survive.
During the last continental shift, Antarctica and the Southern Ocean became isolated in the South where temperatures stay around freezing. Icefish lost all their competition and were able to adapt their bodies to survive such harsh conditions.
Colder water contains more oxygen, so icefish developed bigger hearts and bigger blood vessels to circulate their blood faster. Also, this clear blood contains proteins that work like antifreeze to keep the fish from becoming a block of ice in the frigid waters.
Whether it's for camouflage or a fluke of nature, see-through animals are highly adaptive creatures with interesting characteristics. Scientists are still learning about how translucency works in animals and why creatures have developed this interesting trait.