Spirobranchus giganteus
Encyclopedia
Spirobranchus giganteus, commonly known as Christmas tree worms, are small, tube-building polychaete
worms belonging to the family Serpulidae
.
S. giganteus is similar to most tube-building polychaetes. It has a tubular, segmented body lined with chaeta
, small appendages that aids the worm with its mobility. As it does not move outside its tube, this worm does not have any specialized appendages for movement or swimming.
The worms's most distinct features are the two "crowns" that are shaped like Christmas-trees. These "crowns" are actually highly modified prostomial
palps which are specialized mouth appendages of the worm. Each spiral is composed of feather-like tentacles called radiole
s, which are heavily ciliated which allows any prey that are trapped in them to be transported straight towards the worm's mouth. While they are primarily feeding structures, S. giganteus also uses its radioles for respiration. It is because of this that the structures are commonly called "gills".
One of the major differences between Christmas-tree worms and the closely related sabellida
fan worms is that the latter do not have any specialized body structures to plug the holes of their tubes with when they withdraw into them. S. giganteus, like the other members of its family possess a modified radiole, usually called the operculum
, that it uses to secure its hole when withdrawn into its tube.
As an annelid
, S. giganteus possesses a complete digestive system. It 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, including pedal ganglia, which are unique to the Polychaeta. Like other polychaetes, S. giganteus excrete with fully developed nephridia. When they reproduce, they simply shed their gametes straight into the water where the eggs (and spermatozoa) will become part of the zooplankton
and can be carried by the currents.
tube around its body. This tube serves as the worm's home and protection. S. giganteus usually bores a hole into an existing head of living coral before secreting its tube, thereby increasing its level of protection.
As sedentary inhabitants of coral reefs, Christmas tree worms feed primarily by filter feeding
. 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.
There are two subspecies recognized by the ITIS, S. gigantea corniculatus and S. gigantea gigantea.
Polychaete
The Polychaeta or polychaetes are a class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. Indeed, polychaetes are sometimes referred to as bristle worms. More than 10,000...
worms belonging to the family Serpulidae
Serpulidae
Serpulidae is a family of sessile, tube-building annelid worms in the class Polychaeta. The members of this family differ from the sabellid tube worms in that they have a specialized operculum that blocks the entrance of their tubes when they withdraw into the tubes. In addition, serpulids secrete...
.
Anatomy and morphology
The worm is aptly named; Both its common and Latin names refer to the two, chromatically hued spiral structures that are most commonly what is seen of the worm by divers. In actuality, these multicolored spirals are merely the worm's highly derived respiratory structures.S. giganteus is similar to most tube-building polychaetes. It has a tubular, segmented body lined with chaeta
Chaeta
A chaeta or cheta is a chitinous bristle or seta found on an insect, arthropod or annelid worms such as the earthworm, although the term is also frequently used to describe similar structures in other invertebrates. The plural form is chaetae or chetae.In the Polychaeta, they are located on the...
, small appendages that aids the worm with its mobility. As it does not move outside its tube, this worm does not have any specialized appendages for movement or swimming.
The worms's most distinct features are the two "crowns" that are shaped like Christmas-trees. These "crowns" are actually highly modified prostomial
Prostomium
Prostomium is the first body segment in annelid worms. It is in front of the mouth, being usually a small shelf- or lip-like extension over the dorsal side of the mouth. It sometimes bears antennae and eyes. It often functions like a kind of overlip when the animal is feeding...
palps which are specialized mouth appendages of the worm. Each spiral is composed of feather-like tentacles called radiole
Radiole
A radiole is a heavily ciliated feather-like tentacle found in highly organized clusters on the crowns of Canalipalpata. Canalipalpata is an order of sessile marine polychaete worms consisting of 31 families...
s, which are heavily ciliated which allows any prey that are trapped in them to be transported straight towards the worm's mouth. While they are primarily feeding structures, S. giganteus also uses its radioles for respiration. It is because of this that the structures are commonly called "gills".
One of the major differences between Christmas-tree worms and the closely related sabellida
Sabellida
Sabellida is a suborder of annelid worms in the class Polychaeta. They are filter feeders with no buccal organ. The prostomium is fused with the peristomium and bears a ring of feathery feeding tentacles...
fan worms is that the latter do not have any specialized body structures to plug the holes of their tubes with when they withdraw into them. S. giganteus, like the other members of its family possess a modified radiole, usually called the operculum
Operculum (animal)
An operculum is an anatomical feature, a stiff structure resembling a lid or a small door that opens and closes, and thus controls contact between the outside world and an internal part of an animal...
, that it uses to secure its hole when withdrawn into its tube.
As an annelid
Annelid
The annelids , formally called Annelida , are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches...
, S. giganteus possesses a complete digestive system. It 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, including pedal ganglia, which are unique to the Polychaeta. Like other polychaetes, S. giganteus excrete with fully developed nephridia. When they reproduce, they simply shed their gametes straight into the water where the eggs (and spermatozoa) will become part of the zooplankton
Zooplankton
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...
and can 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
Spirobranchus giganteus is commonly found embedded in entire heads of massive corals. Like members of its family, it can secrete a calcareousCalcareous
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:...
tube around its body. This tube serves as the worm's home and protection. S. giganteus usually bores a hole into an existing head of living coral before secreting its tube, thereby increasing its level of protection.
As sedentary inhabitants of coral reefs, Christmas tree worms feed primarily by filter feeding
Filter feeder
Filter feeders are 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 feeding are clams, krill, sponges, baleen whales, and many fish and some sharks. Some birds,...
. 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.
Importance to humans
While the worm itself has no commercial fishery importance, it is of interest to marine aquarists and divers everywhere. The variously colored worm crowns make extremely popular underwater photographic subjects for sport divers. Many aquarists that have miniature reef aquariums purposely include heads of coral that S. giganteus specimens inhabit.Conservation status
As the species is widespread and relatively common, there are no conservation efforts focusing on this species (or Polychaetes in general).Etymology and taxonomy
Spirobranchus essentially translates to "spiral gills", referring to the worm's unique crown.There are two subspecies recognized by the ITIS, S. gigantea corniculatus and S. gigantea gigantea.