Behold: the king ragworm.

Underwater photographer Alexander Seminov was kind enough to let me to post some of his photographs, and they really are something special. Pictured is Alitta virens, commonly known as the sand worm or king ragworm. And btw, these things can grow to over 120 cm long.

Found in the northern hemisphere where the water is shallow, brackish and temperate, they hide those pretty, iridescent green, blue and yellow colours in U-shaped burrows dug down into the sediment. From here they’ll snare their prey of small worms, crustaceans and molluscs in much the same way as the dreaded bobbit worm - shooting up through their burrows to strike with their two pincer-like teeth before retreating back down to feed on their prize.

But sometimes they'll need to leave the safety of their burrows to scavenge for food scraps, and when things get particularly lean, they’ll emerge to swallow the top layer of sediment so they can live off the nutrients in the settled detritus. At moments like these, the king ragworm is particularly vulnerable to becoming a meal itself, and in response to this, it's figured out a pretty nifty way of keeping watch for predators.

In 2005, a team led by Gordon Watson of the University of Portsmouth's Institute of Marine Sciences observed the responses of king ragworms to three different extracts - king ragworm extract; extracts from its very close relative, Nereis diversicolor; and extracts from its common predator, the flatfish. The N. diversicolor extract didn't prompt much of a response, but the king ragworm extract prompted them to significantly reduce their feeding and other out-of-burrow activities. While the detection of flatfish extract resulted in more tentative feeding activity, the response of the king ragworms to this was no where near as spooked as it was when they detected extracts of their peers.

The team suggested that this could indicate the use of chemical signals by king ragworms to judge the risk of predation in their area. For example, chemical signals given off by flatfish extract could indicate that there is a predator nearby, which is bad news. But chemical signals given off by extracts from other king ragworms could indicate that something in the area is actively damaging king ragworms, which is very bad news. The king ragworm was accordingly named the first known annelid worm - part of a large group of segmented worms that includes earthworms and leeches - to use chemical signals from other members of its species as a warning that there might be active predators nearby.

This careful strategy could have something to do with the species’ relatively long life span of three years (if it's not hauled up by fisherman for bait first). Close relative N. diversicolor typically only lives for about half as long.

This is the slender ragworm (Nereis pelagic). With its Christmassy green, gold and red colouring, this little guy only grows to between 6 and 21 cm long, but what it lacks in length, it makes up for in head appendages. It’s got two antennae, two palps - which are those large appendages near the mouth - and four pairs of tentacles.

It’s also impossibly adorable. In 1959, R.B. Clark from the Department of Zoology at the University of Bristol collected a few hundred slender ragworms and gave them glass tubes to live in like they would their burrows in the wild. Over several months he watched as many of them were inexplicably displeased with their own glass tubes and very interested in their neighbour’s identical glass tube. Fights, friendships and embarrassing knots ensued.

First, the fights and friendships:

If this worm is inadequately housed, it invades neighbouring tubes, and if these are already occupied, fighting between the invader and the occupant often ensues ... If one or other worm has not been driven from the tube within 3–4 minutes, fighting ceases abruptly and the two worms live in the tube.


Fighting involves lots of biting in a very tight space.

The fighting didn’t always occur between two ragworms in the same tube though - Clark reported that if the occupant does not immediately react to the intruder, the intruder will sometimes wiggle itself under the occupant, and if the occupant doesn’t attempt to evict it, both worms agree to live in the same tube.


Clark does go on to say that in some cases if an invader is successful at evicting the original occupant, it’ll recuperate for a few minutes before continuing to pursue the losing ragworm. On one occasion, a slender ragworm was so paranoid about keeping its glass tube that it picked a fight with a neighbouring ragworm, just in case. Fights conducted outside the tubes also involved lots of biting, plus some vigorous thrashing.

And then the knots:

"Worms not accommodated in tubes crawl over each other and even become tangled together in knots."

Dying. I’m dead.

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Hitchhiking Jellyfish, Gonad-Loving Parasites and the Skeleton Shrimp


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