Depth
Phallusia · Marine Life

Phallusia Mamillata

Phallusia mamillata

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 Phallusia
Species mamillata

Tunicate

Identification & Biology

  • IdentificationA large, solitary sea squirt with a soft, translucent white body and two prominent siphon openings. The body is rounded and somewhat lumpy, with the internal branchial basket (gill structure) often visible through the translucent tunic.
  • SizeBody height up to 15 cm. Diameter up to 10 cm. One of the largest solitary tunicates in the Mediterranean.
  • Social HabitSolitary. Permanently attached to hard surfaces. Filter feeds by pumping water through an internal gill basket.
  • HabitatRocky walls, harbour structures, pier pilings, and any hard substrate in sheltered water.
  • Depth0 to 60 m. Common in sheltered shallow waters.
  • Feeds OnPlankton, bacteria, and organic particles filtered from the water.
  • DistributionEastern Atlantic and throughout the Mediterranean Sea. Common in Maltese waters, particularly in harbours.
  • DescriptionPhallusia mamillata is the largest solitary sea squirt commonly encountered in Malta. Its translucent white body, often tinged with blue or green, is a familiar sight on harbour walls and pier pilings. The internal branchial basket visible through the tunic is a beautiful, intricate structure. Large individuals can filter hundreds of litres of water per day, playing an important role in maintaining water clarity.

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.

Phallusia Mamillata species card

Biology

Behaviour & Diet

Feeding Strategy

One of the most efficient filter feeders among Mediterranean tunicates, capable of processing several litres of water per hour through its large pharyngeal basket. It captures bacteria, phytoplankton and fine detrital particles on a continuously secreted mucus sheet.

Filter feeder

Reproduction

A hermaphrodite that spawns eggs and sperm through the atrial siphon, with cross-fertilisation the norm. Tadpole larvae are free-swimming for only a few hours before settling on hard substrate and undergoing rapid metamorphosis.

Broadcast spawner

Behaviour & Defence

Its thick, cartilaginous tunic studded with bumps provides strong physical protection and is difficult for predators to pierce. The tunic also contains mildly acidic vanadium compounds that discourage grazing.

Tough tunic

Dive with diveshack

Where to Encounter in Malta

The following dive sites offer strong habitat match for Phallusia mamillata. 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.

View dive site ›
5-50m
Gozo

Blue Hole

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

View dive site ›
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