The immortal jellyfish, scientifically known as Turritopsis dohrnii, is a unique species celebrated for its ability to potentially live forever. This tiny, translucent creature possesses the remarkable capability to revert to its juvenile polyp stage from its mature medusa form, effectively evading death and restarting its life cycle. This article delves into the diet and feeding habits of this fascinating invertebrate, exploring how it sustains itself throughout its complex life cycle.
An Overview of the Immortal Jellyfish
The immortal jellyfish, also known as the Benjamin Button jellyfish, stands out as one of the only known animals with full regenerative capabilities. Unlike true jellyfish, which belong to the class Scyphozoa, the immortal jellyfish is a hydrozoan (class Hydrozoa). It was first named Turritopsis nutricula in 1883 by German marine biology student August Friedrich Leopold Weismann. Its ability to revert back into polyps after reproducing is unique, a trait discovered accidentally by biologists Christian Sommer and Giorgio Bavestrello in the 1980s.
Physical Characteristics
The immortal jellyfish is almost invisible, resembling an ice cube or glass. Its body is bell-shaped and transparent, with a minuscule height and diameter of approximately 0.18 to 0.4 inches, making it smaller than a pinky nail. The vibrant red stomach, which has a cruciform shape in its cross-section, largely occupies its body. Inside the transparent membrane, immortal jellyfish have a hydrostatic skeleton called a mesoglea, a jellylike substance mostly consisting of water. The epidermis (skin) in the cap has a dense cluster of nerve cells that forms a large ring shape above the radical canal, a common feature for cnidarians. Younger immortal jellyfishes, which are around 0.04 inches in size, have 8 tentacles, while adult ones can have up to 80-90 tentacles.
Habitat and Distribution
Initially discovered in the Mediterranean Sea, the immortal jellyfish now inhabits worldwide coastal areas featuring tropical and temperature waters. Its spread has been facilitated by hitchhiking in the ballast water of long-distance cargo ships. Colonies have been established worldwide, with notable populations occurring in warmer coastal areas of North America (including California, Florida, and Panama) and along the coasts of Okinawa and other southern Japanese islands.
Feeding Habits and Diet
The immortal jellyfish is a carnivore with a diet consisting of small creatures it can consume in one of two ways: passively as a hydroid on the ocean floor or actively as a drifting medusa.
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Diet Composition
The typical diet of the immortal jellyfish includes:
- Zooplankton
- Fish eggs
- Larvae
- Small mollusks
- Small crustaceans
- Other microscopic marine organisms
- Sometimes, even plants
Feeding Strategies
Immortal jellyfish employ different feeding strategies depending on their life stage:
Polyp Stage: As immature polyps attached to the ocean substrate, they passively capture any passing prey.
Medusa Stage: As free-swimming medusae, they actively hunt using their stinging tentacles. The tentacles are lined with nematocysts (stinging cells) that they use to paralyze and capture prey by injecting venom into their victims. The tentacles are also used to pull paralyzed prey toward the mouth. Immortal jellyfish can also expand their bells, creating an area of negative pressure that helps to suck in water and prey or pulls prey closer to their tentacles. Alternating water uptake and expulsion creates a thrust that allows them to move up, down, and sideways in the water column.
Ingestion and Digestion
Turritopsis dohrnii ingests food and excretes waste through its mouth. Jellyfish digest their meals very quickly, which is essential for maintaining their buoyancy. If food remained in their system for an extended period, it would impede their ability to float properly.
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Life Cycle and Reproduction
The immortal jellyfish reproduces both sexually and asexually, but it is not hermaphroditic. The sexually mature medusa stage reproduces by the spawning and fertilization of eggs with sperm, while the sexually immature polyps reproduce by budding. It is the unique life cycle with transformation back into the polyp state that can result in so many genetically identical offspring and no limit on lifespan.
Sexual Reproduction
In sexual reproduction, the sperm fertilizes the eggs, after which the egg develops. The jellyfish hatch as larvae, called planula, and swim out on their own. Helping to propel them through the water are small hairs called cilia which are on their tiny, oval-shaped bodies. After a few days, it is time for the next stage of the life cycle and the planula larvae drop down to the ocean floor and attach themselves to a rock. They then undergo transformation into a cylindrical colony of polyps, which become a parent hydroid colony of genetically identical, free-swimming medusae through spawning.
Asexual Reproduction: Transdifferentiation
The most remarkable aspect of the immortal jellyfish is its ability to revert from the medusa stage back to the polyp stage through a process called transdifferentiation. This occurs when the jellyfish experiences physical damage, environmental stress, starvation, or old age.
During transdifferentiation:
- The medusa's bell contracts.
- The tentacles deteriorate.
- It loses the ability to swim, becoming a ball of tissue that settles to the ocean floor.
Over the next 24-36 hours, the homogeneous cells of the cyst differentiate into those needed for the polyp stage-which will later develop buds that detach and form into several immature medusae again. This process can repeat indefinitely, allowing the immortal jellyfish to avoid old age-that is, if environmental conditions are favorable enough, and the individual organisms are not eaten, succumb to disease, or are killed in another way.
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Predators
Despite their unique ability to revert to the polyp stage, immortal jellyfish are still vulnerable to predators. Adults may be eaten by a host of predators, including penguins, fish, sea turtles, sea anemones, and other jellyfish. While they are in the polyp stage, immortal jellyfishes can wind up as meals for sea slugs.
Conservation Status
The International Union for Conservation of Nature and Natural Resources (IUCN) has yet to assess the immortal jellyfish. Due to its presence in marine habitats worldwide, the species does not appear to be threatened. However, its spread as an invasive species warrants attention, although it has not yet been linked to any major ecological or economic problems.