Moon jellyfish, scientifically known as Aurelia aurita, are a widely recognized species found in oceans across the globe. These marine invertebrates are often encountered in coastal waters. Their distinct physical characteristics help to identify them.
The Translucent Bell and Its Dimensions
The most prominent feature of the moon jellyfish is its bell, which has a characteristic saucer-like or flattened dome shape. This bell is remarkably translucent, often appearing almost entirely clear. Its gelatinous composition, over 95% water, provides structure and allows light to pass through. Moon jellyfish bells typically range from 10 to 40 centimeters (4 to 16 inches) in diameter, though a more common size falls between 15 to 35 cm. This transparent, disc-like body pulsates rhythmically, allowing the jellyfish to propel itself.
Identifying Internal Features
Four horseshoe-shaped structures, the gonads, are a distinctive feature visible through the translucent bell. These reproductive organs are clearly visible and symmetrically arranged, resembling a four-leaf clover when viewed from above. Typically opaque, these gonads can exhibit subtle coloration, often appearing as whitish, blueish, or pinkish markings. Their prominent placement near the center of the bell distinguishes the moon jellyfish from other species, and their characteristic horseshoe shape remains a constant identifier.
Fringe and Feeding Structures
Along the margin of the moon jellyfish’s bell is a fringe of numerous short, fine tentacles. Unlike many other jellyfish species that possess long, trailing tentacles, the moon jellyfish’s tentacles are delicate and relatively short. These tentacles are equipped with stinging cells, known as nematocysts, which are used to capture small prey such as plankton and tiny crustaceans. Extending from the underside of the bell, around the mouth, are four frilly oral arms. These structures are typically longer than the marginal tentacles and play a crucial role in feeding, moving captured prey from the tentacles towards the jellyfish’s mouth for digestion.
Variations in Color and Glow
While moon jellyfish are predominantly known for their translucent or whitish appearance, their diet can influence subtle color variations in their bell and gonads. Depending on the pigments present in their food sources, such as plankton, algae, or crustaceans, their bodies can sometimes display faint hues. These colors may include shades of pink, blue, purple, or even yellowish tones. Some species of moon jellyfish are also capable of bioluminescence, meaning they can produce their own light. This glow is typically subtle, resulting from a chemical reaction within their bodies. This bioluminescent ability can serve various purposes, including startling potential predators or acting as a “burglar alarm” to alert other marine life to danger.