Arrow worms have existed for around 500 million years, but only now scientists - including marine biologist Katja Peijnenburg from Naturalis Biodiversity Center - have been able to determine their place in evolutionary history. In their publication in Current Biology of 21 January 2019, they also question the classical view that complex organisms are descended from simple ancestors.
Picture left: The arrow worm Pterosagitta draco, collected from the Atlantic and photographed alive on board a research vessel by Katja Peijnenburg. This is one of the species used in the study.
Photo right: The head of the arrow worm Sagitta setosa, collected in the North Sea. The unique jaw structure is clearly visible here: two rows of sharp teeth and hooks to grab and eat their prey. Photographed by Jan van Arkel and Katja Peijnenburg.
The first ever drawing of an arrow worm ever collected in Dutch coastal waters, by Martinus Slabber, from 1778.
Unique footage of an arrow worm slowly swallowing another chaetognath, tail first, showing of its impressive jaws.
Katja filmed these during an expedition on the Atlantic Ocean in 2017.