Depth
Bolma · Marine Life

Chestnut Turban

Bolma rugosa

0-40m
Depth Range
Variable
Max Size
Mediterranean
Distribution
0-40m
Depth Range
Variable
Max Size
Reef & Open
Habitat
Carnivore
Diet
Solitary
Social
LC
IUCN Status
Kingdom Animalia
Genus Bolma
Species rugosa

Mollusc

Identification & Biology

  • IdentificationA large, heavy sea snail with a thick, rounded shell covered in a rough, textured surface. Reddish-brown to chestnut in colour, often encrusted with coralline algae and other organisms. The operculum (trapdoor) is thick and calcareous.
  • SizeShell diameter up to 8 cm. One of the larger gastropods on Mediterranean reefs.
  • Social HabitSolitary. Slow-moving grazer found on rocky surfaces. Often partially hidden under overhangs or in crevices.
  • HabitatRocky reefs, boulder fields, and areas with good algal cover. Prefers stable hard substrates.
  • Depth5 to 80 m. Common between 10 and 50 m.
  • Feeds OnAlgae and encrusting organisms scraped from rock surfaces using a ribbon-like radula.
  • DistributionMediterranean Sea and adjacent eastern Atlantic. Present in Maltese waters.
  • DescriptionBolma rugosa is a common but easily overlooked gastropod on Maltese reefs, its encrusted shell blending seamlessly with the surrounding rock. The thick, calcareous operculum that seals the shell opening was historically collected and used in jewellery and decorative arts. This species plays a useful role in controlling algal growth on reef surfaces.

Range

Habitat & Distribution

Found across the Mediterranean, inhabiting reef & open 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

Reef & Open 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.

Chestnut Turban species card

Biology

Behaviour & Diet

Feeding Strategy

A herbivorous grazer that scrapes microalgae and biofilm from rocky surfaces using a robust radula, feeding primarily at night.

Algae grazer

Reproduction

Broadcast spawns into the water column during warmer months. Fertilised eggs develop into planktonic veliger larvae before settling on rocky substrate.

Broadcast spawner

Behaviour & Defence

Retreats into its thick, rounded shell and seals the aperture with a solid calcareous operculum, forming an effective barrier against predators.

Operculum seal

Dive with diveshack

Where to Encounter in Malta

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

5-30m
North Malta

Cirkewwa

Rocky reef with caves, arches and ledges hosting a rich diversity of reef species.

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5-50m
Gozo

Blue Hole

One of the Med's most famous reef dive sites. Rocky walls and archways covered in life.

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18-36m
South Malta

Um El Faroud

The wreck lies on a sandy bottom surrounded by rocky reef -- a diverse habitat attracting reef species.

View dive site ›
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