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What are underwater worms?

Updated: Sep 11, 2021

Weird and wonderful. We feel that divers might not give enough attention and love to worms!

Most people like fish and sea turtles and wouldn’t say they’re that interested in worms and yet a large portion of the questions guides get on dives are about worms. Worms, you say? Aha, but not any worms, sea worms; and sea worms and their various cousins are very cool, colourful and bizarre unlike their terrestrial counterparts.

Christmas tree worms

Colourful? Yup think of those cool little Christmas tree worms, they’re colourful and they hide when you sweep water across them then timidly pop out again. They’re aptly named because they do indeed look like funky little colourful Christmas trees. Those pretty tiny tentacles, radioles, are heavily ciliated and can trap prey and bring it to the worm’s mouth. They also serve as gills allowing the worm to breathe. A great favourite with novice divers, kids, photographers, Santa Claus, everyone really.

Christmas tree worms in Nusa Penida Bali

Feather duster worms

Like the Christmas tree worms, they hide when you swish at them, they’re even more common and the amusement derived from making them hide never wears off. Some can have a beautiful collar of radioles as big as 10 cm long. Certain small species can bend over and extend their tentacles to the sea floor to collect food and scraps.They’re also very pretty in an ethereal, vaporous way like an evanescent nebula, one minute it’s there, barely, one minute it’s gone. They’re poetic, for worms that is.

Feather worm Nusa Penida Bali

Spaghetti worm

There’s also the spaghetti worm, which mystified me for quite a while. Those long threads, that come in a variety of colours, running along the substrate retract when you swish them and had me puzzled for ages and to this day, I’ve still not seen the whole body of the strange tentacles’ owner. Look them up on the internet, they’re strange looking things. The crazy part is that the worm is only a few centimetres long but it’s tentacles can stretch up to a metre and have a little gutter like groove with hair like cilia in them that can carry food along to the mouth. They can also curl the tentacle around larger bits of food and drag it to the mouth. If a tentacle gets cut off it grows back and some species of butterfly fish like to feed on the tentacles. Cool weird critters.

Spaghetti worm Nusa Penida Bali

Bristle worms

I first got interested in them when doing a fluorescent light dive, they were the stars of the show, shinning off the black sand like gems on velvet. Some species are bioluminescent. They are also the great cleaners and best shell mates, living with other organisms and cleaning up all the scraps and dirt. Other species are parasitic or tube dwelling and burrowing, others yet pelagic and free swimming and found from shallow tropical reefs to cold waters and abysses to deep sea vents. Finally, they survived 5 mass extinctions so you could say they’re old school and pretty cool.

Bristle worm diving Indonesia

Flat worms

If you like nudibranches, flat worms may also pique your interest, many species are beautiful like nudis, resemble them and are often confused with them. Yet, they are more closely related to liver flukes and intestinal worms! They come in a variety of colours and glide across the sea bottom scavenging scraps and food bits. Next time you cannot find what species that nudi is, check if it’s a flatworm!

Flat worm diving in Indonesia

Synaptid Sea Cucumber

Clearly a sea cucumber is not a worm and their (only?) main point in common is that they are weird looking invertebrates. However, I get so many questions about this particular sea cucumber that I decided to add it to my worm collection as the odd one out. This bizarre looking creature, often described as looking like a living moving intestine, has tentacles at one end that continuously collect food scraps by adhesion. Common tropical species can grow up to three metres long. Gerald Durell, a famous British naturalist, had this reaction on first sight of the animal: “At first, I could not believe that these weird objects were alive. I thought they must be strange, dead strands of some deep-sea seaweed (…) Closer inspection showed me that they were indeed alive, unlikely though it seemed”. Next time you see one, you’ll know its name!

Sea cucumber diving in Indonesia


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