Comb jellies are marine creatures in the phylum Ctenophora, which includes around 150 known species. These organisms can be found all over the world, sometimes acting as invasive species in areas where they are not native, and causing environmental problems or difficulties in the fishing industry. They are very unusual-looking creatures, and some people find them quite beautiful, while others consider them to be pests in regions where they have proliferated at the expense of other marine organisms.
Although comb jellies have “jelly” in their name, they are not related to jellyfish. Their bodies are roughly egg-shaped, typically with two trailing sticky tentacles. The outside of the jelly's body is covered in a pair of translucent skins which surround a jelly-like membrane, and the inside has a number of basic anatomical structures. The most notable structure is the “comb” for which the jellies are named. Each jelly has multiple combs, long ridges covered in cilia which run along the body. The movements of the cilia propel the creature through the water, allowing it to pursue prey.
Comb jellies are carnivores, pursuing a wide range of marine organisms. They vary in size from around the size of a pinky to the size of a small child, and they reproduce sexually, generating eggs which hatch into larvae. The larvae go through a planktonic stage which involves drifting through the ocean without the ability to move freely before they develop into fully grown adults. Several species remain planktonic as adults, catching prey as it drifts through the ocean with them.
The body of the comb jelly is translucent, and it may be colorless, orange, yellow, red, or black. Many live in regions of the ocean where they can be readily observed and identified, although some species prefer deeper waters, and these creatures are ideally adapted to life in the ocean. Their bodies are lightweight, posing minimal resistance, and the jelly membrane allows comb jellies to go quite deep without being damaged by the high pressure. Some produce chemical sensors which they use to detect passing prey.
Because comb jellies do not have stinging cells, they are not harmful to people. Many of them are bedecked with rainbow colors in the daylight, thanks to the refraction of light through their transparent bodies. Their sticky tentacles, however, can entrap prey, including other jellies. Some examples of well-known comb jellies include sea gooseberries and Venus' girdle.