Nature's Coolest: Marine Invertebrates
There's so much nature out there to appreciate that it can be hard to keep track of it all! Each installment of this series highlights five little-known critters that I think are cute, cool, crazy, or zany. This time we're looking at marine invertebrates.
The pom-pom crab has a unique approach to defense and foraging. It holds stinging anemones in each of its specialized claws to ward off predators and snag prey. If one of its anemones dies it will carefully split the remaining one in half to replace it.
Crinoids are a relative of the more well-known starfish. They begin their lives fixed to the ocean bottom. Some will remain this way forever and others will become unstalked as they mature. The potentially free-floating ones are referred to as feather stars. Their feathery arms can flap rhythmically to filter out food and provide basic locomotion. Most of the time they will be anchored to some sort of substrate, but when they let go to find a new spot it's an incredible sight.
Proof that love knows no bounds, pistol shrimp are known to bunk up with open-minded gobies.
Pistol shrimp build burrows in the sediment, and if the circumstance are right they are happy to share them with gobies. The goby gets a nice burrow to call home and the pistol shrimp gets a lookout. The shrimp don't have very good vision, so when they leave the burrow they keep an antenna in contact with their companion goby; if there's any sudden movement they know to retreat.
This shrimp is also one of the loudest sea creatures. When a fish swims nearby, it snaps its oversized claw to create a cavitation bubble. The corresponding pressure wave stuns or even kills the target fish. It also uses the snapping noise to communicate with other shrimp. At high densities they can create a cacophony strong enough to hide a submarine from sonar detection.
Blue dragons are nudibranchs that float around on the surface of the ocean. Technically they float upside down, although with these types of organisms the concept of right-side up becomes less straightforward. Their diet mainly consists of jellyfish, especially the notoriously venomous Portugese man-o-war. After consuming a venomous jellyfish, blue dragons are somehow able to incorporate some of the stinger cells into their own defensive sacs. These are concentrated at the tips of their fin-like appendages. The venom might be secondhand, but it's no less potent.
Ctenophora are a diverse group of invertebrates ranging in size from a few millimeters to more than a meter. They move using rows of cilia that diffract light into a rainbow of colours. Like jellyfish, they are simple but highly efficient tentacled predators. I can remember feeling pure awe the first time I saw them in a nature documentary. I think it might have been the deep sea episode of Planet Earth.