Chrysaora achlyos

The black sea nettle (Chrysaora achlyos), sometimes informally known as the "black jellyfish" due to its dark coloration, is a species of jellyfish that can be found in the waters of the Pacific Ocean. Its range is thought to be from Monterey Bay in the north, down to southern Baja California and Mexico[2], though there are reports of sightings as far north as British Columbia.[3] It is a giant jellyfish, with its bell measuring up to 1 m (3 ft) in size, and its oral arms extending up to 6 m (20 ft) in length.[2] Despite its size and occasional proximity to Pacific coastal cities, the Black sea nettle was only recognized and scientifically described as a separate species in 1997,[1] though misidentified pictures of the jellyfish had been taken in 1925.[2] It has the scientific distinction of being the largest invertebrate discovered in the twentieth century.[4]

C. achlyos

While sightings have been rare, when they are seen it is often as part of a massive swarm of the creatures, such as those that occurred in surface waters off the coast of Baja California and southern California in 1989, 1999 & 2010.[5]Interestingly, these sightings seem to coincide with incidents of red tides, which consist of the zooplankton that Black sea nettles feed upon.

The sea nettle is radially symmetrical, marine, and carnivorous. Its mouth is located at the center of one end of the body, which opens to a gastrovascular cavity that is used for digestion. It has tentacles that surround the mouth to capture food. Nettles have no excretory or respiratory organs.

Feeding habits

Black sea nettles are carnivorous. They generally feed on zooplankton and other jellyfish.[6] Nettles immobilize and obtain their prey using their stinging tentacles. After that, the prey is transported to the gastrovascular cavity where it is digested.

Defense mechanisms

Each nettle tentacle is coated with thousands of microscopic nematocysts; in turn, every individual nematocyst has a "trigger" (cnidocil) paired with a capsule containing a coiled stinging filament. Upon contact, the cnidocil will immediately initiate a process which ejects the venom-coated filament from its capsule and into the target. This will inject toxins capable of killing smaller prey or stunning perceived predators. On humans, this will most likely cause a nonlethal, but painful stinging sensation which can last for forty minutes.[7]


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