Comb jellies are marine invertebrates found drifting throughout the world’s oceans. Also known as ctenophores, these creatures are recognized for their delicate, often transparent bodies and iridescent colors that shimmer as they move. They add to the diverse tapestry of marine life.
Distinctive Features
Comb jellies possess several features that set them apart from other marine organisms, including their comb-like rows. These eight rows, composed of fused cilia, run along their bodies and are used for movement. As these cilia beat, they diffract light, producing a shimmering, rainbow-like effect. Many species of comb jellies also exhibit bioluminescence, producing their own light through chemical reactions. This light serves various functions, such as defense or communication.
They have unique prey-capturing cells called colloblasts. These specialized adhesive cells, found on their tentacles, release a sticky substance to ensnare prey. Unlike true jellyfish, comb jellies do not possess stinging cells (nematocysts) and are harmless to humans. This absence of stinging cells is a primary distinction between the two groups, despite their superficial similarities. Their bodies are typically gelatinous and transparent, consisting mainly of water, with a biradial symmetry that gives them a distinct body plan.
Habitat and Locomotion
Comb jellies inhabit marine environments across the globe, from the surface waters to the deep sea. They are found in a wide range of temperature zones and can tolerate varying salinity levels. Many species are pelagic, living in the open ocean and drifting with currents.
Their primary mode of locomotion involves the rhythmic beating of their comb rows. These fused cilia propel the comb jelly through the water. Comb jellies are the largest known animals that use cilia for propulsion. This ciliary movement contrasts with the pulsating bell contractions seen in true jellyfish.
Feeding and Reproduction
Comb jellies are carnivorous predators, consuming a variety of small marine organisms. Their diet primarily consists of zooplankton, including copepods, as well as larval fish, and even other comb jellies. They capture prey using their sticky colloblast cells on their tentacles. Once prey adheres to the colloblasts, the comb jelly retracts its tentacles to bring the food to its mouth. Some species, like the sea walnut (Mnemiopsis leidyi), are voracious feeders and can consume significant amounts of food.
Reproduction in most comb jelly species involves hermaphroditism, meaning individuals possess both male and female reproductive organs. They typically release eggs and sperm directly into the water, where fertilization occurs. While external fertilization is common, some species can self-fertilize. Comb jellies are known for their rapid reproductive rates, with some species able to reach sexual maturity in as little as two weeks after hatching and produce gametes daily if food is plentiful.
Ecological Role
Comb jellies play a part in marine food webs, acting as both predators and prey. As predators, they feed extensively on zooplankton, which includes the eggs and larval stages of various fish and invertebrates. By consuming these organisms, they help regulate zooplankton populations. This predatory behavior can also have broader ecosystem impacts.
Certain comb jelly species, such as Mnemiopsis leidyi, have become invasive outside their native ranges. When introduced to new environments, often via ship ballast water, their rapid reproduction and feeding habits can lead to significant population booms. These large populations can outcompete native species for food resources and consume fish eggs and larvae, leading to declines in fish stocks and disruptions to local fisheries. Comb jellies also serve as a food source for larger marine animals, including some fish, sea turtles, and other comb jelly species.