Jellyfish (jellies) are a diverse group of fairly primitive creatures. They lack a brain, bones, teeth and fins, but don't need them for survival. Their kind has been around a long time. Jellies bodies are more than 95% water and they can vary greatly in size, from miniscule to several meters in diameter. They live on plankton, microscopic shrimp and other small oceanic creatures; in turn jellies are eaten by sea turtles and other larger animals. Jellies have a complex life cycle, beyond the scope of this blog; the interested reader is referred to this link for more detailed information.
I'm not particularly fond of encountering jellyfish when I'm swimming (because of their stingers), but I do enjoy studying them in tanks at an aquarium. The way they slowly float and tumble, invisible muscles pulsating in the gently moving water, the soft light that highlights their details -- terrific visual experience!
I've not seen a better exhibit of Jellyfish than one I saw at the Monterey Bay Aquarium. The following photos represent part of their collection and were taken during one of my visits.
MOON JELLIES
One of the more common species you'll see in aquariums. Moon jellies have a translucent, rounded bell, short tentacles and four oral arms.
PURPLE-STRIPED JELLIES
More colorful than moon jellies, these large striped jellies have a very painful sting.
PACIFIC SEA NETTLES
Sea nettles have rather long tentacles and frilly mouth-arms covered with stinging cells that paralyze their food.
CRYSTAL JELLIES
They are very pale -- nearly transparent -- and have long, thin tentacles. I think they're quite cool!
UPSIDE-DOWN JELLIES
Why wouldn't the Jellyfish world have a member that does everything upside down? This is an unusual creature. It lies with its bell on the sea floor and tentacles facing the sun. Symbiotic algae within the jellies photosynthesize because of this.
SPOTTED JELLIES
This species has a round bell with blunt clublike appendages. They are a yellow-brown color (due to symbiotic algae growing in their tissues). Spotted jellies are also known as "lagoon jellies",
SOUTH AMERICAN SEA NETTLE
Found mostly along the Pacific coast of South America -- ranging from Peru to southern Chile, with smaller numbers along the Atlantic coast. Its bell can measure up to a meter in diameter.
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