* Chloe McCardel abandoned attempt after 11 hours in water
* Had hoped to reach Florida's Key West on Friday
Australian long-distance swimmer Chloe McCardel was making good headway in calm seas at dusk when she suddenly hit a stinging swarm of jellyfish, eventually forcing her to abandon her quest to become the first person to swim from Cuba to Florida without a shark cage.
"It felt like explosions hitting my body," she told reporters on Thursday after returning to Key West.
McCardel, 28, was pulled from the water on Wednesday night. She said the stings were so numerous she was paralyzed from the waist down by the pain and forced to gave up the attempt 11 hours into the 103 mile (166 km) marathon swim.
Despite being stung repeatedly on her arms, legs and back by venomous box jellyfish tentacles McCardel kept going for 20 to 30 minutes, said team spokesman, Matt Nelson.
When crew members saw her trying to remove a tentacle from her face and mouth, one of her team jumped into the water to help, but the damage was done.
Aboard one of the team's support vessels, McCardel's husband and crew chief, Paul McCardel, decided it was too risky to continue and ordered her out of the water.
"We were worried about breathing issues. It just got too dangerous," Nelson said.
Unlike bee stings, jellyfish tentacles keep stinging as long as they are in contact with the skin. "The tentacles wrap around you and they have to be peeled off," he said.
McCardel said she did not remember being stung in the mouth but was unable to speak for three hours after being pulled out of the water on Wednesday.
Jellyfish, not sharks, had been the team's biggest concern all along. "You can't see them, they are translucent and they can just ambush you in the middle of the night," said Nelson.
McCardel had a team of scientists in the United States to help guide her through the powerful and unpredictable current that has stymied many previous attempts, and was aware of the hazards posed by jellyfish.
McCardel said she was advised she would have a "jellyfish-free" crossing. "The information I got was wrong," she said.
She said that before she left for Cuba, U.S. Customs officials confiscated an experimental ointment to prevent jellyfish stings supplied to her team.
McCardel plunged into a calm, crystal-clear sea at Havana's Hemingway Marina early in the morning, hoping to cross the Straits of Florida in about 60 hours and reach Key West on Friday.
Her swim was timed with the season and moon phase to minimize the presence of the box jellyfish, which had plagued previous swimmers, including American Diana Nyad who was stung repeatedly in August on her fourth failed attempt.
Only one person, Australian Susie Maroney in 1997, has completed the Cuba-U.S. swim, but she used a shark cage, which helps cut through the water.
Last summer, British-born Australian Penny Palfrey got tantalizingly close to the Florida Keys but could not finish when she swam into a Gulf Stream eddy that pushed her in the wrong direction.
McCardel said she has no plans to make another attempt and planned to spend the next 24 hours recuperating.