Hydra, Found in Ponds and Lakes, See and Hunt Without Eyes

Posted on March 24, 2012

Hydra magnipapillata, a polyp found in ponds, lakes, and streams, reacts to light even thought it has no eyes. The hydra hunt during the day are are known to move, looping end over end, in response to light. New research indicates that the stinging cells (cnidocytes) in hydra tentacles are linked through a simple nervous system to primitive light responsive cells. The hydra uses its tentacles - which contain barbed, poisonous stinging cells called cnidocytes - to stun animals like the water flea, Daphnia, before it eats them alive. The hydra also uses its stinging tentacles as a defense against an attack by other animals.

Researchers from the University of California, led by Dr David Plachetzki, discovered that the light sensitive protein opsin found in sensory cells is able to regulate the firing of harpoon-like cnidocytes. These light sensitive neurons are found integrated into the stinging cnidocytes as well as desmoneme cnidocytes, used to grasp prey, and sticky isorhiza, which help the hydra to summersault at 10cm a day. The linking of opsin to cnidocytes explains how hydra are able to respond to light even though they do not have eyes.

Dr. Plachetzki says, "Not only did we find opsin in the sensory neurons that connect to cnidocytes in the hydra, but we also found other components of phototransduction in these cells. These included cyclic nucleotide gated ion channels (CNG) required to transfer the signal and a hydra version of arrestin, which wipes the phototransduction slate clean for a second signal."

The research paper, "Cnidocyte discharge is regulated by light and opsin-mediated phototransduction," by David C Plachetzki, Caitlin R Fong and Todd H Oakley , is published here in BMC Biology.

ANIMALS