Just Bobbing On By, But with a Sting in the Tale

By Annabel Thomas

For The Bali Times

SEMINYAK ~ Sea jellies (aka jellyfish) are – rather surprisingly, to me, the first time I heard it – members of the same family, Phylum Cnidaria, as stony corals, soft corals, horny corals, fire corals, precious corals, sea anemones and hydroids.

That said, all Cnidarians have specialized stinging capsules or cells called nematocysts and anyone who has spent time in and around the ocean knows that sea jellies, anemones, hydroids and fire corals can (and do) sting you…

Like other Cnidarians, sea jellies are simple, multi-celled organisms which either live in colonies or solitarily, and that have a basic body structure consisting of a radically symmetrical flashy sac with a ring of tentacles encircling a single opening. It is these tentacles around the mouth that contains the nematocysts.

Nematocysts consist of an inverted barbed thread connected to a venom sac, often with a small trigger-like structure (cnidocil) that acts as a receptor for the physical stimulus that discharges the nematocyst into the victim’s skin. The venom is delivered along a groove that runs the length of the thread and is strong enough to kill or paralyze the prey ready for consumption. The more the prey struggles, the more securely it becomes trapped as it comes into contact with other nematocysts which also shoot out their venomous threads.

Obviously the toxins vary in strength, from those found in corals to more dangerous forms such as those found in the Sea Wasp, Portuguese Man-of-War and Box sea jellies.

They have two main parts: the umbrella-shaped bell and the tentacles. The bell is a gelatinous mess that is usually translucent but may be tinged purple, brown or green. As digestion – which takes place in the gut cavity inside the bell – reduces prey to a soupy substance, the bell will temporarily turn opaque.

Sea jellies propel themselves by rhythmic pulsations of the bell which push water out of the concave space underneath.

They range in size from microscopic to really very large: the Lion’s Mane sea jelly can have a bell that measures 1 meter across with 800 tentacles of up to 10 meters in length.

Incidentally, vinegar will kill the stinging cells within 30 seconds, so it’s always a good idea to have some on hand when you’re having a day at the beach: an easy way to avoid a miserable child (or adult).

The writer is director of AquaMarine Diving – Bali.

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