Arrow Worm

The Chaetognatha, or chaetognaths, are a phylum of predatory marine worms that form a major component of plankton worldwide. Commonly known as arrow worms, they are mostly pelagic, though about 20 percent of known species are benthic and can attach to algae and rocks. They are found in all marine waters, from surface tropical waters and shallow tide pools to the deep sea and polar regions. Most chaetognaths are transparent and torpedo-shaped, though some deep-sea species are orange, and they range in size from 2 to 120 millimeters.