Friday, January 18, 2013

Tube Anemones (Phylum Cnidaria: Order Ceriantharia) of Singapore

Tube anemones (phylum Cnidaria, class Anthozoa, subclass Hexacorallia, order Ceriantharia) are solitary animals with radially symmetrical bodies that live in mucous tubes. They have a simple body comprising a stomach (coelenteron) and an oral disc with a mouth surrounded by tentacles. They do not have an anus, and hence the mouth performs both functions of ingesting food and removing waste.  Like other cnidarians, they possess explosive, harpoon-like cells called cnidocytes. Each cnidocyte contains a secretory organelle (cnidae), which can be a nematocyst that discharges a harpoon-like stinger carrying toxins, a ptychocyst that discharges sticky substances, or a spirocyst that discharges lasso-like threads. Hence while cnidocytes are often called "stinging cells", they do perform other functions apart from stinging.

Tube Anemone (Order Ceriantharia)
The tube which the cerianthid lives in is constructed from discharged nematocyst threads, mucus and bits of marine debris. Much of the tube is buried in the sandy or muddy substratum, and only a small part is exposed. Some species may attach to rocks or other hard structures underground.

Tube Anemone (Order Ceriantharia)
These solitary hexacorals are also known as peacock anemones as they come in a variety of colours and the extended tentacles resemble the opened tail of a male peacock with some imagination. There are two types of tentacles – around the mouth are shorter tentacles (a few centimetres long) which aid in transferring food particles to the mouth, and surrounding the shorter tentacles are much longer ones (can be over 10 cm long) which sting and capture small prey.

Tube Anemone (Order Ceriantharia)
During low tide or when they are disturbed, the tube anemone may retract into the tube.

Tube anemone feeding
Most tube anemones are mostly filter feeders, feeding on tiny organic particles such as plankton. At times, they also sting and feed on small animals such as the clams above.

Tube anemone feeding
This tube anemone caught a small fish, which it had stung and paralysed.

Tube Anemones (Order Ceriantharia)
Tube anemones are generally solitary, though sometimes clusters of two or three individuals can be seen.

Tube anemones can reproduce asexually by budding, or sexually by releasing eggs and sperm into the water. In fact, more cerianthid larvae have been described than adult species!

The classification of tube anemones is very complex, and often involves looking at the internal structure and the cnidom (array of nematocyst types and sizes). Hence, identification in the field is very difficult unless the species has very distinctive external features. However, as the tube anemones of Singapore are very poorly studied, I will not attempt to identify them. Below is just a picture gallery of some of the tube anemones that I have photographed. It is likely that the majority are just variations of the same species.

White Tube Anemone (Order Ceriantharia)
The whole of this tube anemone is white in colour. It is usually found on sandy substrates among seagrass.

Tube Anemone (Order Ceriantharia)
The body column and the base of the tentacles of this tube anemone are brownish orange, while most part of the tentacles are white. I have seen it in sandy lagoons and among seagrass.

Peacock Anemone (Order Ceriantharia)
The inner tentacles and oral disc of this tube anemone are orange, but the base of the outer tentacles is greenish, followed by a brownish band. The rest of the animal is white. I have seen it on sandy substrates among seaweed and seagrass.

Tube Anemone (Order Ceriantharia)
This tube anemone is all orange, and is usually found on sandy shores, sometimes among seagrass.

Tube Anemone (Order Ceriantharia)
The oral disc and inner tentacles of this tube anemone are brown, and the outer tentacles are greenish. I have seen it in a sandy lagoon.

The entire animal is purple for this tube anemone. I have seen it on very soft, muddy substrates.

Tube Anemone (Order Ceriantharia)
This tube anemone has a dark purple oral disc, with whitish inner tentacles, and slightly purplish outer tentacles. It is usually found near coral reefs, or on sandy areas among corals.

Tube Anemone (Order Ceriantharia)
This tube anemone has brown inner tentacles and white outer tentacles. I have seen it on sandy substrates, and those mixed with pebbles and shell fragments, sometimes among seagrass.

Tube Anemone (Order Ceriantharia)
This tube anemone appears similar to the previous one, but the lower part of the outer tentacles is brown. It was seen in a seagrass meadow on firm sand.

Tube Anemone (Order Ceriantharia)
This tube anemone has dark brown inner tentacles, and light brown outer tentacles. It was seen on sandy substrates mixed with bits of shell fragments.

Tube Anemone (Order Ceriantharia)
This small tube anemone has outer tentacles with yellow, brown and slightly purplish bands. The oral disc and inner tentacles can be light or dark brown. It is usually seen on slightly muddy substrates.

Tube Anemone (Order Ceriantharia)
This transparent tube anemone usually has a black ring near the rim of the oral disc. It is usually on firm substrates with a mixture of sand, pebbles and shell fragments, usually near coral reefs.

Tube Anemone (Order Ceriantharia)
The tentacles can be slightly brownish or reddish brown.

Tube Anemone (Order Ceriantharia)
This tube anemone is all black in colour. I have only seen it on soft muddy substrates.

This tube anemone appears to have tentacles that are partially fused nearer to the base. The inner tentacles are very short.

  • Den Hartog, J. C. 1977. Descriptions of two new Ceriantharia from the Caribbean region, Pachycerianthus curacaoensis n. sp. and Arachnanthus nocturnus n. sp., with a discussion of the cnidom and of the classification of the Ceriantharia. Zoologische Mededelingen 51 (14): 211-242.
  • Erhardt, H. and D. Knop. 2005. Corals: Indo-Pacific Field Guide. IKAN-Unterwasserachiv, Frankfurt. 305 pp. 
  • ETI BioInformatics. 2012. Marine Species Identification Portal. Retrieved Jan 15, 2013, from 
  • Fautin, D. G. 2011. Hexacorallians of the World. Retrieved Jan 15, 2013, from 
  • Ruppert, E.E. and R.D. Barnes. 1991. Invertebrate Zoology (International Edition). Saunders College Publishing. U.S.A. 1056 pp.
  • Tan, L. W. H. and P. K. L. Ng. 1988. A Guide to Seashore Life. The Singapore Science Centre. Singapore. 160 pp.
  • World Register of Marine Species. 2012. Retrieved Jan 15, 2013, from

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