''Spirobranchus giganteus'', commonly known as the Christmas tree worm, is a tube-building
polychaete
Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are ...
worm belonging to the family
Serpulidae
The Serpulidae are a family of sessile, tube-building annelid worms in the class Polychaeta. The members of this family differ from other sabellid tube worms in that they have a specialized operculum that blocks the entrance of their tubes whe ...
.
Anatomy and morphology

Both its common and Latin names refer to the two chromatically hued spiral structures, the most common feature seen by divers. The multicolored spirals are highly derived structures for feeding and respiration.
''Spirobranchus giganteus'' is similar to most tube-building polychaetes. It has a tubular, segmented body of an approximate length of 3.8 cm (1.5 in) covered with
chaeta
A chaeta or cheta (from Greek χαίτη “crest, mane, flowing hair"; plural: chaetae) is a chitinous bristle or seta found in annelid worms, (although the term is also frequently used to describe similar structures in other invertebrates such ...
e, small appendages that aid the worm's mobility. Because it does not move outside its tube, this worm does not have any specialized appendages for movement or swimming.
The worms' most distinct features are two "crowns" shaped like
Christmas tree
A Christmas tree is a decorated tree, usually an evergreen conifer, such as a spruce, pine or fir, or an artificial tree of similar appearance, associated with the celebration of Christmas. The custom was further developed in early modern G ...
s. These are highly modified
prostomial palps, which are specialized mouth appendages. Each spiral is composed of feather-like tentacles called
radioles, which are heavily
ciliated
The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike projec ...
and cause any prey trapped in them to be transported to the worm's mouth. While they are primarily feeding structures, ''S. giganteus'' also uses its radioles for respiration; hence, the structures commonly are called "gills".
One major difference between Christmas tree worms and other
Sabellida
Sabellida is an order of annelid worms in the class Polychaeta
Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions cal ...
fan worms is that the latter do not have any specialized body structures to plug their tube holes when they withdraw into them. ''S. giganteus'', like other members of its family, possesses a modified radiole, usually called the
operculum, that it uses to secure its hole when withdrawn into its tube.
As an
annelid
The annelids (Annelida , from Latin ', "little ring"), also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecol ...
, ''S. giganteus'' possesses a complete digestive system and has a well-developed closed circulatory system. Like other annelids, these worms possess well-developed nervous systems with a central brain and many supporting
ganglia
A ganglion is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system there are both sympath ...
, including
pedal ganglia
A pedal (from the Latin ''pes'' ''pedis'', "foot") is a lever designed to be operated by foot and may refer to:
Computers and other equipment
* Footmouse, a foot-operated computer mouse
* In medical transcription, a pedal is used to control pl ...
, unique to the
Polychaeta
Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are ...
. . Like other polychaetes, ''S. giganteus'' excretes with fully developed
nephridia
The nephridium (plural ''nephridia'') is an invertebrate organ, found in pairs and performing a function similar to the vertebrate kidneys (which originated from the chordate nephridia). Nephridia remove metabolic wastes from an animal's body. Neph ...
. When they reproduce, they simply shed their gametes straight into the water where the eggs and spermatozoa become part of the
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 ...
to be carried by the currents.
Range and distribution
Christmas tree worms are widely distributed throughout the world's tropical oceans. They have been known to occur from the Caribbean to the Indo-Pacific.
Ecology
''S. giganteus'' is commonly found embedded entirely in heads of massive corals, such as stony corals ''
Porites
''Porites'' is a genus of stony coral; they are small polyp stony (SPS) corals. They are characterised by a finger-like morphology. Members of this genus have widely spaced calices, a well-developed wall reticulum and are bilaterally symme ...
'' and
brain coral
Brain coral is a common name given to various corals in the families Mussidae and Merulinidae, so called due to their generally spheroid shape and grooved surface which resembles a brain. Each head of coral is formed by a colony of geneticall ...
s. Like members of its family, it can secrete a
calcareous
Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.
In zoology
''Calcareous'' is used as an a ...
tube around its body. This tube serves as the worm's home and protection. ''S. giganteus'' usually settles onto an existing head of living coral before secreting its tube, thereby increasing its level of protection as coral tissue overgrows the calcareous tube. When the worm retreats into its tube, the opening is shut using an operculum, which is further protected by sharp, antler-shaped spines.
As
sedentary inhabitants of coral reefs, Christmas tree worms feed primarily by
filter feeding
Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feedi ...
. They use their brightly colored radioles to filter microorganisms from the water, which are then deposited straight into the worm's digestive tract.
Few organisms are known to feed on tube-borne polychaetes and ''S. giganteus'' is no exception. The symbiotic relationship between ''S. giganteus'' and its host corals is still poorly understood, but occasionally the movement of the operculum can abrade the coral tissue, and that mortality of the coral tissue is enhanced when the worm's operculum hosts filamentous algae.
Importance to humans
While the worm itself has no commercial fishery importance, it is of interest to marine aquarists and divers. The variously colored worm crowns make extremely popular underwater photographic subjects for
sport divers. Many aquarists who have miniature reef aquaria purposely include heads of coral that ''S. giganteus'' specimens inhabit.
Conservation status
As the species is widespread and relatively common, no conservation efforts focus on this species (or polychaetes in general). This species was thought to be exclusively found in coralheads, however they have also recently been described as epibionts on the giant clam species ''
Tridacna squamosa
''Tridacna squamosa'', known commonly as the fluted giant clam and scaly clam, is a species of bivalve in the family Cardiidae. MolluscaBase eds. (2022). MolluscaBase. Tridacna squamosa Lamarck, 1819. Accessed through: World Register of Marine S ...
'' in the
Gulf of Thailand
The Gulf of Thailand, also known as the Gulf of Siam, is a shallow inlet in the southwestern South China Sea, bounded between the southwestern shores of the Indochinese Peninsula and the northern half of the Malay Peninsula. It is around in l ...
.
The conservation status of the host species which it inhabits varies.
Etymology and taxonomy
''Spirobranchus'' essentially translates to "spiral gills", referring to the worm's unique crown. Two subspecies are recognized by the ITIS: ''S. giganteus corniculatus''
and ''S. giganteusa giganteus''.
References
Further reading
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Gallery
Image:Corals sea worms.JPG, Christmas tree worm from Papua New Guinea
Papua New Guinea (abbreviated PNG; , ; tpi, Papua Niugini; ho, Papua Niu Gini), officially the Independent State of Papua New Guinea ( tpi, Independen Stet bilong Papua Niugini; ho, Independen Stet bilong Papua Niu Gini), is a country i ...
.
Image:Spirobrancheus giganteus.jpg, Christmas tree worms (''Spirobranchus giganteus'') from East Timor
East Timor (), also known as Timor-Leste (), officially the Democratic Republic of Timor-Leste, is an island country in Southeast Asia. It comprises the eastern half of the island of Timor, the exclave of Oecusse on the island's north-we ...
.
Image:Christmas Tree worms.jpg, ''Spirobranchus giganteus'' embedded in a brain coral
Brain coral is a common name given to various corals in the families Mussidae and Merulinidae, so called due to their generally spheroid shape and grooved surface which resembles a brain. Each head of coral is formed by a colony of geneticall ...
in a reef in Bonaire
Bonaire (; , ; pap, Boneiru, , almost pronounced ) is a Dutch island in the Leeward Antilles in the Caribbean Sea. Its capital is the port of Kralendijk, on the west (leeward) coast of the island. Aruba, Bonaire and Curaçao form the ABC ...
.
Image:ChristmasTreeWorm-SpirobranchusGiganteus.jpg, ''Spirobranchus giganteus'', Vieques, Puerto Rico
Vieques (; ), officially Isla de Vieques, is an island and municipality of Puerto Rico, in the northeastern Caribbean, part of an island grouping sometimes known as the Spanish Virgin Islands. Vieques is part of the Commonwealth of Puerto Ri ...
Image:Christmas tree worm (Spirobranchus giganteus).jpg, Elbow Reef, Florida
Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, a ...
.
Image:Reef0232.jpg, In Hawaii
Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only ...
.
Image:Spirobranchus giganteus at Gili Lawa Laut.JPG, At Gili Lawa Laut (near Komodo, Indonesia
Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...
)
External links
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{{DEFAULTSORT:Spirobranchus Giganteus
Fauna of the Philippines
Serpulidae
Animals described in 1766
Fauna of the Caribbean
Fauna of the Dominican Republic
Invertebrates of the Indian Ocean
Fauna of the Pacific Ocean
Taxa named by Peter Simon Pallas