Regulan blood worms
From: Star Trek: Enterprise
Caption: Regulan Blood Worm from Phlox's onboard supply.
These creatures are very useful for filtering toxins from humanoids. Dr. Phlox carries a supply onboard Enterprise NX-01, but he prefers the fresh ones from Regulus. When Travis Mayweather was given an antigenic compound that caused a bad reaction, Phlox suggested using these to filter out the toxins.