Essay by Villasis-Peregrino I. & A.E. Ramos-Santiago (edited by Professor Krista Williams)
In the amazing world of marine animals, there are approximately one million animals. Among these animals are the bioluminescent ctenophores (also known as “comb jellies” or “sea walnuts”). The ctenophores are a phylum of marine planktonic invertebrates. In this essay we will talk about some characteristics of the ctenophores, such as their feeding, reproduction and ecological importance.
The ctenophores are natural predators: They have long tentacles with structures called coloblasts. The ctenophore’s tentacles extend, and when its prey touches the coloblasts, the tentacles discharge adhesive substances to catch their prey and discharge the stinging cells (Ruppert & Barnes 1996). After the ctenophore’s tentacles have caught its prey, muscular contractions direct the tentacles to its mouth. The mouth of the ctenophores gives way to the pharynx. The epithelium of the pharynx contains large quantities of glandular cells that produce digestive enzymes, and the cilia of the pharynx allow these organisms to digest its food (Enríquez-García et al. 2013). Although these organisms have a small diet, digestion and secretion are often complex.
The ctenophores are bioluminescent, meaning that they naturally glow in the dark due to a unique physical feature that allows them to generate their own light internally. They have two types of reproduction: sexual and asexual. These organisms are able to regenerate almost any part of their body and they can regenerate even half a body. Asexual reproduction occurs when the organism releases small fragments of its body and each fragment is regenerated into a full adult. In the case of sexual reproduction, most of the ctenophores are hermaphrodites and only some species are separate sexes. Pelagic ctenophores expel their gametes through the mouth towards the sea water and that is where fertilization takes place, which can be a self-fertilization or a cross-fertilization (Brusca & Brusca 2003). Later they will become embryos that grow rapidly to be transformed into a plantotrophic larva called a cidipoide. The ctenophores are easily confused with the cnidarians: the development of ctenophores is very different from that of the cnidarians, which have a planula larva, contrary to the cidipoide larva of the ctenophores.
The ctenophores have great ecological importance. The main role of these organisms in the trophic chain is to feed on other groups of marine invertebrates and be an intermediary of some parasites. However, there have also been ecological catastrophes due to these organisms. In 1980 in the Black Sea, two species of ctenophores were accidentally introduced by ballast water. These were large predators of anchovies, and this had a great effect on the Black Sea fishing industry, thus causing the collapse of the anchovy fishing industry. Currently it is not known that other problems could be caused by the absence of the ctenophores. Even though they are such small animals, they have great importance.
The ctenophores have the characteristic of being a large predator, due to their great capacity of reproduction. As a predator of some marine invertebrates, it has a great ecological importance. On the other hand, if its population is not controlled, it can economically affect the fisheries. It is of great importance that the studies of the ctenophores be deeper in order to recognize how it could affect the ecology of other organisms.