Twin Fan Worm | diveshack Marine Life Guide

Polychaete

Identification & Biology

IdentificationA tube worm with a distinctive pair of spiral fan crowns, each forming a separate whorl of banded feathery tentacles. The double fan pattern distinguishes it from single-fan species like Sabella. The tubes are soft and parchment-like, often covered in sediment.
SizeFan diameter up to 8 cm. Tube length up to 20 cm.
Social HabitSolitary or in small groups. Lives permanently in its tube. The twin spiralling fans are extended to feed and retract rapidly when disturbed.
HabitatRocky reefs, under boulders, and on mixed substrates in sheltered areas.
Depth0 to 50 m. Common in shallow to moderate depths.
Feeds OnPlankton and suspended organic particles captured by the feathery radioles.
DistributionEastern Atlantic from the British Isles to the Mediterranean Sea. Present in Maltese waters.
DescriptionBispira volutacornis is one of the more distinctive fan worms in the Mediterranean, easily recognised by its paired spiral fans. The banded pattern of the radioles is often beautifully marked in brown, cream, and orange. Like all sabellid worms, it is extremely sensitive to vibration and light changes, retracting the fans in a fraction of a second. Slow, careful approaches with minimal fin movement give the best chance of observation.

Range

Habitat & Distribution

Found across the Mediterranean, inhabiting sandy / muddy environments. Active from the surface down to 40m depth.

Where Malta divers have spotted this species

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Sightings are logged by divers using our What Did You See? dive-log tool. View the full live sightings map.

Detail

Preferred Environment

Sandy / Muddy habitats, typically at depths of 0-40m. Most commonly encountered by divers at the shallower end of its range.

Encounter Tips

Best approached slowly and calmly. Avoid casting shadows directly over the animal. Neutral buoyancy and patience increase encounter success significantly.

Biology

Behaviour & Diet

Feeding Strategy

Extends its twin spiral fans into the current to intercept suspended phytoplankton, bacteria and fine detritus. Mucus and cilia on the radioles sort particles by size, directing food to the mouth while rejecting coarse sediment.

Filter feeder

Reproduction

Sexes are separate, with gametes released into the water column during warmer months for external fertilisation. Planktonic larvae settle on hard surfaces and begin constructing a flexible, leathery tube from secreted mucus and trapped sediment.

Broadcast spawner

Behaviour & Defence

Retracts both fan crowns into its tough, flexible tube at remarkable speed when it detects changes in light or water pressure. The tube opening is narrow relative to the worm's body, making it difficult for predators to extract the animal.

Rapid retraction

Dive with diveshack

Where to Encounter in Malta

The following dive sites offer strong habitat match for Bispira volutacornis. All are accessible on a guided dive with diveshack.

3-18m

Comino

Blue Lagoon

Extensive sandy floor with excellent visibility. A prime habitat for benthic species that shelter in the sandy channels.

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5-22m

South Malta

Ghar Lapsi

Sheltered cove with sandy patches between rocky outcrops. The sandy areas at 8-15m are rich in benthic marine life.

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8-30m

North Malta

Cirkewwa

Sandy channels flanking the reef system provide excellent habitat for bottom-dwelling species.

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IUCN Red List Least Concern

Conservation Status

This species is assessed as Least Concern on the IUCN Red List. Mediterranean populations face ongoing pressure from fishing activity, habitat degradation, and climate-driven changes to prey availability.

Source: iNaturalist Guide #888
by Lesley Clements (CC BY-SA)
diveshack Mediterranean Marine Life guide