Jellyfish are one of the most well-known creatures of the ocean. Many people have felt the pain of their stinging tentacles, and countless others have observed them floating listlessly through the water, trailing their tentacles behind them. However, there is a lot more to jellyfish than the regular sightings at the beach. They are one of the most uniquely designed creatures in Creation. In part one of this article, I will be introducing you to jellyfish, and telling you a little bit about them. I will follow up with a second article explaining how they were created very good and why they challenge evolutionary dogma.
Jellyfish come in various shapes, sizes, and designs. Just a quick online photo search for the term “jellyfish” reveals the variation among the various species of jellies. With that much variation, what is there that stays the same across the species? Jellies are radially symmetric, meaning if they are cut in half in any direction, the two halves will be identical. Most jellies have a decentralized nervous system called a nerve net. Essentially this means that the nerves do not report to a central “brain”. Instead, they respond individually to stimuli and transmit this response through their rhopalial lappet, a ring-like structure that connects the nerve nets. Some jellies have light spots called ocelli, which are eye-like structures which do not form images. Instead, they detect light concentrations, allowing jellies to see in a blurred, outlined, black and white fashion. They have no digestive system, instead relying on an internal body cavity called the gastrovascular cavity, which handles the digestion and absorption of nutrients. Some species have the ability to contract their bodies and produce some independent motion but most rely on currents to move them. Because of their hydrostatic skeleton, which allows them to contract their body, they can easily navigate around tight obstacles. Because their skin is so thin, jellies can absorb oxygen directly from the water around them through their skin, meaning they do not need gills.
Jellies are members of Phylum Cnidaria. They are bearers of what is referred to as a cnidocyte or a nematocyte. Essentially what this cell amounts to, is a spring-loaded stinging weapon, that fires upon contact. It also has the ability to reload itself to be used again. There are three types of cnidocyte, each of which will be examined here. The first kind is called a penetrant. When discharged, it breaks the surface of the skin or scale it contacts and infuses the area with a paralyzing agent. This allows the jelly to draw its prey into its gastrovascular cavity. A glutinant works in a similar fashion, except instead of paralyzing the prey, the cnidocyte sticks to the prey and draws them into the gastrovascular cavity. The third variety, called a volvent, essentially works like a coiled rope. It fires, wraps itself around whatever the prey happens to be and draws it into the inner portion of the jelly. The cnidocytes, whichever method they use, all perform the same function for the jelly, that of capturing prey and bringing them into the jellies mouth.
Jellies have a very unique form of reproduction. They go through a long and complicated life cycle, each step of which is crucial to the survival of the jelly. There is a chart below illustrating this from the National Science Foundation. The form we think of as the jellyfish is called the Medusa. The genders are separate in jellies, though asexual reproduction does happen, particularly in the polyp form. The medusa produces the egg and sperm. In rare occasions, the medusa will asexually form These combine and the larva settle out of the plankton onto the bottom. Once they settle onto the ocean floor, they form a the polyp stage of reproduction. The polyp is what forms new jellyfish. As the polyp grows, it goes through a process called budding. Essentially, the budding process causes a new jellyfish to break off from the polyp and join the plankton. The max lifespan the larger jellies is approximately six months while some of the smaller jellies have a lifespan of merely hours.
Jellies have a unique role in the ecosystem. As part of the plankton themselves, they largely feed on the floating algae and zooplankton. As such, they are highly dependent on these microbiological food sources for survival. When jellies appear in huge numbers, as they have been in the last decade or so, the underlying cause is generally an increase in these microbiological food sources. A large grouping of jellies such as this is referred to as a bloom.
There is a lot more to discuss regarding jellies, particularly in relation to how they challenge evolutionary theory. However, I will leave that for the next article which should appear in a few days.