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Tube Anemone

Cerianthus membranaceus

Family: Cerianthidae | Genus: Cerianthus

Tube Anemone (Cerianthus membranaceus)

Tube Anemone

Cerianthus membranaceus

Family: Cerianthidae | Genus: Cerianthus

Marine environments | Carnivorous and planktivorous | Atlantic Ocean and Mediterranean Sea

Tube anemones are remarkable marine engineers, constructing a permanent refuge in the form of a mucus-lined tube buried within the seabed. Unlike typical sea anemones, which attach themselves to rocks, tube anemones spend their entire lives inside these self-built tubes. The tube is formed from specialised mucus secretions that harden on contact with seawater and can extend up to one metre beneath the sediment surface. Only their elegant tentacles remain visible above the seabed.

Tube anemones possess cnidocytes—specialised stinging cells found both on their tentacles and within the tube—which play a vital role in defence and in immobilising prey. They are widely distributed throughout the eastern Atlantic and the Mediterranean Sea and, because they do not rely on sunlight, they are able to thrive in permanently dark marine environments. When threatened, they can retract completely into their tube within a fraction of a second, disappearing instantly beneath the seabed.

Geographical distribution

Atlantic–Mediterranean distribution. In the Mediterranean Sea, the species has been recorded along the northern coastline, including the coasts of Spain, France, Italy, the Croatian Adriatic and the Aegean Sea, as well as from Port Said (Egypt) through the Dardanelles and the Sea of Marmara.

Tube anemone
Tube anemone at Poema del Mar

Icono de Anfibios Habitat

The tube anemone inhabits soft-sediment seabeds, favouring areas sheltered from strong currents and rich in plankton. Although specimens have been recorded at depths ranging from 2 to 20 metres, it is most commonly encountered between 15 and 40 metres.

Nevertheless, its bathymetric range is broad, with recent records documenting its presence on sandy seabeds at depths ranging from less than 80 metres to more than 200 metres.

Icono de Anfibios Lifestyle and behaviour

Tube anemones (Cerianthus membranaceus) are sessile, solitary animals that spend their entire adult lives within self-constructed tubes buried in the seabed. They remain permanently attached to the same tube, extending their tentacles from the opening to capture food carried by water currents.

Social behaviour:

  • Strictly solitary organisms.

  • Each individual occupies its own tube.

  • No social interactions between individuals.

Daily activity:

  • Extend their tentacles mainly at night and during feeding periods.

  • Can retract completely into the tube when threatened.

  • Feed continuously while their tentacles remain extended.

  • Activity patterns may vary according to depth and food availability.

Reproduction:

  • Sexual reproduction, with individuals being either dioecious (separate sexes) or hermaphroditic.

  • Gametes are released into the water for external fertilisation.

  • Free-swimming planula larvae drift in the plankton before settling.

  • During metamorphosis, structures such as the tentacles, septa and pharynx develop before permanent settlement.

  • No parental care.

Relationship with their environment:

  • Tube construction: specialised mucus secretions harden to form a sticky tube reinforced with sediment particles, mucus and cnidocytes.

  • Cnidocytes (stinging cells): present in both the tentacles and the tube, providing defence and assisting in prey capture.

  • Two crowns of tentacles: the outer crown consists of long feeding tentacles that capture prey, while the shorter inner crown transfers food towards the mouth.

  • Gastrovascular cavity: the central cavity functions both as the mouth for food intake and as the opening for waste elimination, reflecting their incomplete digestive system.

  • Rapid withdrawal: can retract entirely into the tube within fractions of a second when disturbed.

  • Independence from sunlight: as they do not harbour symbiotic zooxanthellae and are therefore non-photosynthetic, they are able to inhabit deeper marine environments.

Icono de Anfibios Diet

Natural habitat

  • Opportunistic suspension-feeding carnivores.

  • They feed primarily on plankton, including both zooplankton and phytoplankton.

  • They capture small crustaceans (such as larvae) and occasionally fish larvae.

  • They also consume suspended particulate organic matter.

Under human care

  • A varied diet consisting of mysis shrimp, enriched brine shrimp (Artemia), and krill.

  • Target feeding close to the tentacles three times per week.

  • Requires moderate water flow to facilitate prey capture.

Icono de Anfibios Conservation status

The tube anemone (Cerianthus membranaceus) has not been assessed individually by the International Union for Conservation of Nature (IUCN) Red List. Nevertheless, like other benthic invertebrates, it may be affected by a range of environmental pressures.

Main threats:

  • Degradation of the seabed: bottom trawling disturbs sediments and destroys its permanent tube.

  • Marine pollution: the accumulation of contaminants in the sediment may adversely affect its health.

  • Climate change: changes in ocean temperature and chemistry may influence its physiology.

Related species

Magnificent sea anemone

Bubble-tip anemone

Jewel anemone