Red Sea-Squirt

(Halocynthia papillosa)




Facts about this animal

Adult Red Sea-Squirts are about 6-12 cm long (maximum 20 cm). The colour (caused by symbiotic micro-algae) is red or vividly orange but paler on the side turned away from light. At depths below 15 m it looks black if no artificial light is used. They are upright and the tubular body is bulbous. The test is rough and finely granulated but clean due to antifouling impregnation. There are two cylindrical siphons equipped with a crown of rigid bristles, used as sensitive elements. The upper one is the oral opening which can be closed to a four-lobed cross; the lateral one is the cloacal exit which can be closed lip-like with two lobes.

Red Sea-Squirts are living solitary. In case of danger they can shut themselves off.

Red Sea-Squirts are active filterers as it is typical for all primitive chordates. There are symbiotic micro-organisms like flagellates and crustaceans living on the internal gills. The inhaled water passes them before it enters the sieve organ. The water is later moved to a chamber surrounding the gills before it is exhaled by any of the two siphons. Digestible components are kept in the filter, covered in mucus and taken away by means of cilia through the oesophagus to the stomach. The intestine is rather long and the anus is situated near the oral siphon.

Reproduction is sexual and takes place in November. Individuals are hermaphrodites and release eggs and sperms at different times to avoid self-fertilization. The larva has a notochord and is planktonic. It soon settles down, head to the ground, and metamorphoses to a small sea-squirt by regressing tail, brain and notochord and turning around all inner organs for 180°. Life last usually one year.

Did you know?
that ascidians like the Red Sea-Squirt produce cellulose to stabilize their test which else is known from plants only? that the Red Sea-Squirt belongs to the same phylum of animals as humans, the so called chordates? that ascidians like the Red Sea-Squirt can and regularly do change the direction in which blood is pumped through the heart, and that the blood is relatively rich in the rare element Vanadium?


Name (Scientific) Halocynthia papillosa
Name (English) Red Sea-Squirt
Name (French) Ascidie rouge, Outre de mer, Vioulet rouge
Name (German) Rote Seescheide
Name (Spanish) Ascidia rojo sangre, Ascidia roja, Pero de mar
Local names Dutch: Rode zakpijp
Italian: Ascidia rossa, Patata di mare
CITES Status Not listed
CMS Status Not listed



Photo Copyright by
Albert Kok



Range Mediterranean Sea and adjacent Atlantic Ocean off Portugal and Madeira
Habitat The Red Sea-Squirt lives at shady places in submarine caves, crevices and precipices or even seagrass meadows from 1 m down to 100 m deep but mostly in 10-15 m depth.
Wild population Unknown because of no commercial value
Zoo population 0 reported to ISIS (2008)

In the Zoo

Why do zoos keep this animal

The Red Sea-Squirt is vividly coloured and relatively large and can therefore be used to show an active filterer of microorganisms within its natural environment among other salt-water organisms in a submarine habitat. In doing this it also helps to keep the tank water clean.