The mantis shrimp is a marine crustacean that typically grows to be 30 centimeters in length and can range from brown to bright neon colors. They have very powerful claws that are capable of inflicting serious damage on victims significantly greater in size than themselves. The mantis’ eye has 16 photoreceptors (compared to the our 3) and can see UV, visible, and polarized light making it the most complex visual system on Earth.
In case you needed one more thing to keep you up at night, meet the Sea Spider: a tiny but sinister looking animal that is not actually an arachnid, but instead probably evolved as a distinct sister lineage to all known arthropods (crustaceans, insects).
Their elongated bodies have so much surface area that they don’t even need a respiratory system, instead exchanging gasses via direct diffusion across the surface of their body and extremities.
Sea Spiders are carnivores and feed on soft tissued animals like sea anemones, by stabbing them with their long, sharp proboscis and sucking the nutrients out of them. Not creepy at all - photo taken at Seacrest Cove 2, Seattle, WA
This is the Diving Bell spider and is the only spider known to live its entire life under water. It breathes air but it does so by trapping air in a bubble and holding onto it with hairs on its abdomen and legs while underwater. This bubble (bell) permits gas exchange with the surrounding water; taking in oxygen and releasing carbon dioxide. The spider will spend most of its time in this bubble and very rarely needs to replenish the air thanks to the gas exchange.