Keeping Marine Worms

Marine worms are a common accidental inhabitant of salt-water aquarium tanks, larvae or juveniles often being introduced along with “living rock”, other marine invertebrates or in natural seawater.

However, a growing number of aquarists have found that they make interesting, attractive and fairly undemanding animals to keep in their own right.

Although they are related to the earthworm, marine worms such as the sedentary Sabella tube worms or the much more active sea-mouse (Aphrodite aculeata) are about as far removed from their familiar garden cousins as its possible to get, both in looks and lifestyle.

Marine Worm Types

Amongst the world’s marine worms there are swimmers, crawlers, burrowers and tube-dwellers. Known as “polychaetes” – meaning many bristled – various species have adapted their bristles to allow them to do everything from actively paddling through the sea, to feeding themselves by filtering small edible items from the water. Marine worms are an impressive group, but perhaps the tube-dwelling “fan” and “feather duster” worms – named after the crown of feeding tentacles around their mouths – are the most striking and easiest to keep. Some of the best species to have in your seawater aquarium include:

• Fan Worm (Filograna implexa); widely distributed throughout tropical seas, this is an attractive animal, the filter “fan” bearing coloured bands of white and pinkish purple.
• Horseshoe Worm (Pomatosteges stellatus); found in the tropical regions of the west Atlantic, this worm has a pinkish U-shaped fan some 1-2 inches (2.5-5cm) across.
• The Magnificent Banded Fan Worm (Sabellastarte indica), also known as the Magnificent Feather Duster Worm; one of the most common of the fan worms sold in the exotic pet trade, it is widespread throughout the world’s tropical waters and really lives up to its name, having a fan around 4 inches (10cm) in diameter, banded in red.
• Pacific Double Crowned Worm (Sabellastarte sanctijosephi); a distinctive species with two fans of unequal size – the smaller one sitting above the larger one.

The Magnificent Tubeworm (Protula magnifica) from the Indo-Pacific is sometimes to be seen for sale, but it is not an easy species to keep in an aquarium. It’s certainly a striking animal – making a chalky tube to live in that may be up to a foot (30cm) in length and as thick as your finger – but one probably best left to experienced aquarists.

Another species which typically proves to be difficult to maintain for any length of time is the Horned Christmas Tree – sometimes called the “Bisma Rock Worm” – (Spirobranchus giganteus). A natural inhabitant of all tropical waters, the appeal of this worm is obvious, its head-end being equipped with a series of smaller and smaller fans, which make it look almost exactly like a miniature decorated Christmas tree. Unfortunately, feeding it can be challenging and it doesn’t tolerate high light levels, which effectively rules it out for the home aquarium.

Caring For Marine Worms

Accommodating marine worms is fairly straightforward, calling for a good-sized tank equipped with aeration, filtration and a power pump to generate a replica of the natural tidal current within the tank. Most of the species commonly available come from warm seas, so an appropriate heater and thermostat will also be needed.

Most marine animals are more sensitive to the build up of nitrates and other chemicals in the water than their freshwater counterparts, so it’s important to pay attention to water quality – efficient filtration and regular partial water changes are essential to keep the tank healthy.

Feeding Marine Worms

Fan and feather duster worms are filter feeders, sifting microscopic creatures and food particles from the water and, obviously, in captivity they will need to be provided with a similar diet. The likes of Daphnia, small brine shrimps and other appropriately sized, shop-bought live foods will be ideal and for many species, mussel-milk – made from the pulverised flesh of mussels – is a good standby.

With their beautifully coloured rosettes of tentacles waving gently in the current, fan worms look far more like exotic marine flowers than second-cousins to an earthworm. If you’re looking for a distinctly different kind of sea-life to keep, then marine worms are definitely worth a look.