Depth
Halocynthia · Tunicates & Sea Squirts

Red Sea Squirt

Halocynthia papillosa

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
Phylum Chordata
Subphylum Tunicata
Genus Halocynthia
Species papillosa

Tunicate

Identification & Biology

  • IdentificationA solitary sea squirt with a stout, barrel-shaped body covered in a tough, leathery tunic. Vivid red to crimson, with two prominent siphon openings at the top (one for drawing water in, one for expelling it). One of the most colourful tunicates in the Mediterranean.
  • SizeBody height up to 10 cm. Diameter up to 5 cm.
  • Social HabitSolitary. Permanently attached to hard surfaces. Filter feeds continuously by pumping water through its body.
  • HabitatRocky walls, overhangs, and cave entrances. Prefers shaded positions.
  • Depth5 to 100 m. Common between 10 and 50 m.
  • Feeds OnPlankton, bacteria, and organic particles filtered from the water through an internal mucus net. Pumps several litres of water per hour.
  • DistributionMediterranean Sea and adjacent eastern Atlantic. Common in Maltese waters.
  • DescriptionHalocynthia papillosa is the most striking sea squirt in the Mediterranean. Its vivid red body stands out against any background and is a favourite subject for underwater photographers. When disturbed, it can contract slightly and squirt water from its siphons (the origin of the common name 'sea squirt'). Like all tunicates, it is a filter feeder that processes large volumes of water daily.

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.

Red Sea Squirt species card

Biology

Behaviour & Diet

Feeding Strategy

Pumps seawater through a perforated pharyngeal basket lined with sticky mucus, capturing bacteria, phytoplankton and suspended organic particles. The constant inflow and outflow create a steady filtering cycle.

Filter feeder

Reproduction

A simultaneous hermaphrodite that cross-fertilises by releasing sperm into the water column while retaining eggs internally. Fertilised eggs develop into free-swimming tadpole larvae that settle within hours.

Broadcast spawner

Behaviour & Defence

Its tough, leathery tunic is reinforced with cellulose-like tunicin and contains distasteful chemical compounds. The bright red colouration may serve as aposematic warning to potential predators.

Tough tunic

Dive with diveshack

Where to Encounter in Malta

The following dive sites offer strong habitat match for Halocynthia papillosa. 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