During chase scenes, movie protagonists often make their getaway by releasing a decoy to cover their escape or distract their pursuer. But this tactic isn’t reserved for action heroes. Some deep-sea animals also evade their predators by releasing decoys – glowing ones.
Karen Osborn from the Scripps Institute of Oceanography has discovered seven new species of closely related marine worms (annelids) that use this trick. Four of these pack up to four pairs of “bombs” near their heads – simple, fluid-filled globes that the worms can detach at will. When released, the “bombs” give off an intense light that lasts for several seconds.
The worms were collected from the Pacific Ocean by remote-controlled submarines. Unfortunately, the small size of the bombs and the low resolution of the sub’s cameras meant that Osborn was never able to film the worms actually releasing their glowing payload in their natural environment (although she did capture some great videos; see bottom of post).
Nonetheless, the specimens she recovered would indeed launch one or two bombs, when they were prodded on any part of their body. If she prodded them further, they would release more bombs, until they ran out. The fact that some worms also carried much smaller globes suggests that they can regenerate them once their supply is exhausted.
In the darkness of the deep ocean, some animals create their own light. Among these is the Hawaiian bobtail squid Euprymna scolopes, which forms a partnership with the luminous bacterium Vibrio fischeri. The squid houses colonies of these bacteria in special light organs, and it can control the brightness and direction of their illuminations. But these organs do much more than produce light – they detect it too.
Deyan Tong from the University of Wisconsin has discovered that the organs generate nervous signals when they sense light and they’re loaded with proteins responsible for detecting it. The light organs are effectively an extra set of primitive eyes, each equipped with its own “iris” and “lens”. The squid comes equipped with a pair of living, ‘seeing’ flashlights.
Scientists have studied the light organ of E.scolopes for over 20 years and its similarity to an actual eye hasn’t gone unnoticed. The core of the organ where the bacteria live is surrounded by a reflective layer of tissue and part of the squid’s ink sac. These can expand and contract like an iris to control how much light escapes the core. The entire package is covered by a thick, transparent tissue – a “lens” – which diffuses the light produced by the bacteria.