WHAT IS JELLYFISH ALL ABOUT?

Figure 1: The life cycle of jellyfish

THE BIOLOGY OF JELLYFISH

The life-cycle of jellyfish is different among the classes. The life cycle of common jellyfish requires an alteration of generations, which they need to pass through two different body forms (SCDNR, 2009). The familiar form that usually found is the dominant medusa form, while the sessile and smaller polyp form occurs only during larval stage. Jellyfish could reproduce sexually or asexually. When they reproduce sexually, the individuals are dioecious, which it will be either male or female. After fertilization occurs, the embryo will developed either inside the female or in brood pouches along the oral arms. Then, it will develop into swimming larvae called planulae and enters the water column. Several days later, the larvae attach themselves to something firm on the sea floor (rocks, shells, etc.) and gradually transform into flower-like polyps called scyphistoma. These polyps use tentacles to feed on microscopic organisms in the water column. Polyps can reproduce asexually by producing buds or cysts that separate from the first polyp and develop into new polyps. When conditions are right, the polyps will undergo a process called strobilation, which produce a larval stage (the strobila) that resembles a stack of saucers. One by one each disc detaches from the end of the strobila and become an ephyra. It is a tiny jellyfish that resembles like the mature form. In a few weeks, the ephyra will grow into an adult jellyfish (medusa), thus completing the complex life cycle. Jellyfish normally live for a few months; however, the polyp stage may be perennial. In this way, each scyphistoma is like a jellyfish factory, churning out dozens of jellyfish. The summary of jellyfish life cycle can be refer to Fig 1.

Here is a brief description of the entire life cycle of a jellyfish:

Fertilization: Like many other organisms, jellyfish are either male and produce sperm or female and produce eggs. When a male jellyfish is ready to mate, it releases sperm in the water through its mouth. When a female jellyfish passes by, these sperms get attached to her eggs. In her mouth, the process of fertilization occurs. Once the eggs are fertilized, they are either stored on the mother's mouth or in brood pouches along her oral arms. In different species of jellyfish, this process may vary and you may find that the eggs are fertilized in the mother's stomach. In some cases, the unfertilized eggs may be stored in the female's oral arms where they get fertilized by sperm in the water.

Planula Larva: After the embryonic stage, the larvae hatch and get transformed into free-swimming planulae. They then leave the security of their mother's body and set out on their own. A plunula has a small oval shape and has tiny hair on its surface that it beats together for movement. But, just like the adult jellyfish, most of its movements are entirely dependent on water tides and currents. Each planula floats around for a few days near the surface of the water and then sinks towards the ocean bottom.

Polyp (scyphistoma): After a planula sinks to the bottom, it attaches itself to a hard stationary surface. This cylindrical planula is attached to the surface at its base; at its top is its mouth surrounded by a few tentacles which gather food. As this polyp grows, it begins to form new polyps from its trunk, forming a polyp hydroid colony. All the polyp members of this colony are attached to each other by tiny feeding tubes. This entire stage in the life cycle of a jellyfish is a sessile stage, because the polyp colony is stationary and attached to a single surface. These colonies are known to grow to very large sizes and can exist for a number of years. Only after the polyp colony has grown to an appropriate size, will the next stage of the life cycle of a jellyfish begin.

Ephyra and Medusa: When the last stage is reached, the stalk of ployp begins to develop horizontal grooves. The topmost groove will free itself from the stalk as a baby jellyfish, known as ephyra. This ephyra will grow in size and become the adult jellyfish we all recognize. This last stage is the asexual reproduction aspect of the jellyfish's life cycle.

coming up next >>> WHAT IS JELLYFISH PROBLEM-RELATED?