Comb jellies (ctenophora) and arrow worms (chaetognatha) are totally unrelated but share similarities because they are both relatively large planktonic predators. Both groups are common all around Iceland, including in Eyjafjörður

Arrow worms are narrow, transparent and streamlined, they even have fins like fishes. At the front they have hooks to grab their prey. They are efficient predators on other plankton and it is probable that they eat great quantities of eggs and larvae of fishes.

Comb jellies look like jelly fishes but are unrelated and usually smaller. The most common species basically look like barrels or balls with eight rows of cilia along their entire body. These move synchronized for swimming. As the arrow worms the comb jellies are efficient predators on other plankton, mostly copepods but probably also fish eggs and larvae.