''Atriolum robustum'' is a

colonial Colonial or The Colonial may refer to: * Colonial, of, relating to, or characteristic of a colony or colony (biology) Architecture * American colonial architecture * French Colonial * Spanish Colonial architecture Automobiles * Colonial (1920 au ...

tunicate A tunicate is a marine invertebrate animal, a member of the subphylum Tunicata (). It is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including vertebrates). The subphylum was at one time ca ...

or sea squirt in the family ''

Didemnidae Didemnidae, or Didemnidæ, is a family of colonial tunicates in the order Enterogona. These marine animals are found in shallow water on the seabed. Members of this family have small zooids that form encrusting colonies. The body of each zooid i ...

''. It is native to the western and central Indo-Pacific where it is usually found anchored to a hard surface in shallow water.

Description

A colony of ''Atriolum robustum'' consists of a number of hollow, urn-shaped

zooid A zooid or zoöid is a single animal that is part of a colonial animal. This lifestyle has been adopted by animals from separate unrelated taxa. Zooids are multicellular; their structure is similar to that of other solitary animals. The zooi ...

s up to long, each with a large circular terminal hole, the atrial siphon, and connected by an encrusting base. The tunic (body wall) is firm to the touch and is perforated by a number of pore-like buccal siphons, each raised on a slight elevation, giving the zooid a pine cone-like appearance. The tunic contains a red pigment but the colour of this is often masked by the presence of yellowish-green

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...

(''

Prochloron ''Prochloron'' (from the Greek ''pro'' (before) and the Greek ''chloros'' (green) ) is a genus of unicellular oxygenic photosynthetic prokaryotes commonly found as an extracellular symbiont on coral reefs, particularly in didemnid ascidians (sea ...

'' sp.) and may only be visible in the interior and at the rim of the atrial syphon. This sea squirt is sometimes confused with ''

Didemnum molle ''Didemnum molle'' is a species of colonial tunicate in the family Didemnidae. It is commonly known as the tall urn ascidian, the green barrel sea squirt or the green reef sea-squirt. It is native to the Red Sea and the tropical waters of the ...

'' but that species has a network of internal channels and exudes

mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous and mucous cells. It is ...

, making it sticky to the touch.

Distribution

''Atriolum robustum'' is found in the tropical western and central

Indo-Pacific The Indo-Pacific is a vast biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the ...

region at depths between about . Its range extends from Madagascar to Australia and Papua New Guinea and includes

Réunion Réunion (; french: La Réunion, ; previously ''Île Bourbon''; rcf, label= Reunionese Creole, La Rényon) is an island in the Indian Ocean that is an overseas department and region of France. It is located approximately east of the island ...

and

Mayotte Mayotte (; french: Mayotte, ; Shimaore: ''Maore'', ; Kibushi: ''Maori'', ), officially the Department of Mayotte (french: Département de Mayotte), is an overseas department and region and single territorial collectivity of France. It is loc ...

Biology

''Atriolum robustum'' feeds on

phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'. Ph ...

zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...

and minute pieces of

detritus In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...

. Water gets drawn into the zooid through the buccal openings, the edible particles are then filtered out and the water current leaves the zooid through the atrial siphon. Sexual reproduction involves sperm being drawn into the body cavity with the inflowing water current and eggs being fertilised internally. The developing embryos are brooded at first. This tunicate is itself eaten by various

predators Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...

including the Egyptian sea star, '' Gomophia egyptiaca'' and the sea snail, '' Gyrineum gyrinum''.

Gallery

Image:Atriolum robustum (Ascidians) growing on Melithaea sp. (Soft coral).jpg, ''Atriolum robustum'' on

soft coral Alcyonacea, or soft corals, are an order of corals. In addition to the fleshy soft corals, the order Alcyonacea now contains all species previously known as "gorgonian corals", that produce a more or less hard skeleton, though quite different f ...

Image:Tunicate medley komodo.jpg, Several species of tunicates in

Komodo National Park Komodo National Park (Indonesian: ''Taman Nasional Komodo'') is a national park in Indonesia located within the Lesser Sunda Islands in the border region between the provinces of East Nusa Tenggara and West Nusa Tenggara. The park includes the ...

. ''Atriolum robustum'' (green) with ''

Polycarpa aurata ''Polycarpa aurata'', also known as the ox heart ascidian, the gold-mouth sea squirt or the ink-spot sea squirt, is a species of tunicate in the family Styelidae. Description ''Polycarpa aurata'' grows to a height of . It has an urn-shaped, ...

'' (purple and yellow), and ''

Rhopalaea ''Rhopalaea'' is a genus of tunicate A tunicate is a marine invertebrate animal, a member of the subphylum Tunicata (). It is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including verte ...

'' spp. (blue)

References

{{Taxonbar, from=Q4817563 Enterogona Animals described in 1983