Most people know not to touch a jellyfish(水母)but some jellies can sting people without touching them—by connecting tiny bits from their body that float off into the sea and move around independently.
Upside-down jellyfish throw small balls of stinging cells in a network of sticky mucus(黏液), to kill prey such as shrimp. “It is as if we could spit out our teeth and they killed thing for us somehow,” says Cheryl Ames at Tohoku university in Japan. “It’s a real revolutionary novelty.”
Upside-down jellyfish, several species of the genus Cassiopea, live in warm coastal waters off Florida, Australia, the Red Sea and southerly parts of the Mediterranean. Their stings aren’t generally seen as dangerous, but there have been occasional reports of “stinging water” around them. “It’s really irritating. You’re constantly being stung on any surface that’s exposed,” says Ames.
Now Ames’s group has found that this happens because the creatures shed hollow balls of stinging cells up to half a millimeter wide. Named cassiosomes, they carry hairs that can make them float around in circles to boost their chances of hitting prey. “It was a really amazing moment when we all took turns in looking through the microscope and saw there were tiny, little things moving about in the mucus,” says Ames. The jellies released cassiosomes and mucus when brine shrimp, their natural prey, were put in their tank. The cassiosomes could kill the shrimp within a minute. In the wild, the dead shrimp are then sucked into the jellies’ body by their pulsating motions. And these jellies tend to float at the bottom of lakes, and extend their networks of mucus to float above them. “The mucus may not be easily visible to swimmers,” says Ames.
The unique feeding mechanism isn’t the jellies main source of nutrients. They also have algae inside them, which photo synthesize. And the reason why the jellies float upside down is to expose these plant cells to the sun. The cassiosomes also contain algae, which might provide the energy for them to float around-they could survive outside the jellies for up to 10 days in the lab.
【小题1】What does Cheryl Ames think of the jellyfish’s way to catch food?| A．Fresh. | B．Mysterious | C．Terrible. | D．Unacceptable. |
| A．They can easily be noticed by the swimmers. |
| B．They can send the shrimp to the jellies themselves. |
| C．They are spread in the mucus released by the jellyfish. |
| D．They use their hair to attract the shrimp. |
| A．To protect themselves from the sun. |
| B．To hide themselves from the enemy. |
| C．To transport algae to the cassiosones. |
| D．To get more energy provided by algae inside. |
| A．Travel abroad. | B．Under the sea. | C．Business. | D．Religion. |
