What is a Ctenophore?

A ctenophore is a small marine animal, usually with two long tentacles, that preys on tiny targets in the ocean’s photic (light) zone, including plankton, fish eggs, larvae, other ctenophores, and other tiny organisms generally around 1 mm in size. Ctenophores are sometimes called comb jellies, despite their relative complexity in comparison to jellyfish. Some ctenophores are bioluminescent, but this is only visible in complete darkness. In an aquarium, ctenophores appear bioluminescent due to rows of fused cilia on its side used for locomotion, which scatter light, producing a beautiful rainbow effect. In the best-known species, Pleurobrachia, the light does not emit from the ctenophore itself, but is created by optical scattering.

The best-known genera of ctenophore is Mnemiopsis, which can be found seasonally in the brackish water off Chesapeake Bay. Like jellyfish, Mnemiopsis and other ctenophores have bodies that consist mostly of water, in this case 97%. The ctenophore is prey for many important larger animals, including sea turtles and a variety of fish.

Ctenophores have several unique cells for hunting and locomotion. The ctenophore has a balance receptor, the statocyst, which works very differently than the inner ear in mammals, but is used to maintain upright positioning in ctenophores as needed. Ctenophore tentacles contain colloblasts, or lasso cells, which are specialized cells that send out sticky threads upon contact with prey. These are different from the jellyfish’s nematocysts, which are instead used to inject toxins, but they share some structural similarities. The release times for these cells are very impressive, in the microseconds or less, and can only be captured by extremely quick-exposure cameras.

Unfortunately, we don’t know as much about ctenophore history as we’d like, because these animals fossilize poorly. Most of what we know is gleaned from observations of ctenophores in laboratories in the present. Although more complex than jellyfish, ctenophores lack a central nervous system, possessing only a decentralized neural net to guide their behavior and reactions. The simplicity of this neural net makes it a potential target for emulation in robotics.

Ctenophores, commonly known as comb jellies, are gelatinous, marine animals distinguished by their eight rows of ciliary plates used for locomotion. Unlike jellyfish, they lack stinging cells and instead possess sticky cells called colloblasts to capture prey. Ctenophores are also bioluminescent, emitting light through chemical reactions within their bodies.

Ctenophores play a crucial role in marine food webs, both as predators and prey. They help control populations of smaller plankton and serve as a food source for larger marine animals. Their bioluminescence can also attract mates and deter predators, influencing behavioral patterns within the ecosystem.

Yes, ctenophores are a widespread group found in all the world's oceans, from the surface to the deep sea. They inhabit a variety of marine environments, demonstrating a remarkable adaptability to different conditions, from polar regions to tropical waters.

Ctenophores are significant in evolutionary biology due to their unique position on the tree of life. Recent genomic studies suggest that they may be one of the earliest diverging animal lineages, potentially reshaping our understanding of animal evolution and the origin of key traits like the nervous and muscular systems.

Ctenophores are capable of both sexual and asexual reproduction. They release eggs and sperm into the water for external fertilization. Some species can also reproduce asexually through fission. While many ctenophores can reproduce year-round, some species in temperate regions may have specific breeding seasons linked to environmental conditions.

Ctenophore populations face threats from ocean acidification, pollution, and habitat destruction. However, they are not currently considered endangered. Their wide distribution and rapid reproduction rates help maintain their populations, but like all marine organisms, they are vulnerable to significant changes in their ecosystems.