Spirobranchus corniculatus

Spirobranchus corniculatus, commonly referred to as the Indo-Pacific Christmas tree worm, is a species of tube-building annelid fanworms in the family Serpulidae.^[1][2] Belonging to the class Polychaeta, it is recognized for its bristle-like tentacles and the presence of a structure called radioles. It is widely encountered and recognized for its unique resemblance to a conifer and its diverse array of colors.^[3] Initially presumed to be part of a species group including Spirobranchus cruciger and Spirobranchus gaymardi, it has been determined to be a singular, morphologically adaptable species inhabiting the Central Indo-Pacific region.^[4]

Spirobranchus corniculatus
Surat Thani, Thailand, 2023
Scientific classification
Kingdom:	Animalia
Phylum:	Annelida
Clade:	Pleistoannelida
Clade:	Sedentaria
Order:	Sabellida
Family:	Serpulidae
Genus:	Spirobranchus
Species:	S. corniculatus
Binomial name
Spirobranchus corniculatus (Grube, 1862)

Description

The Christmas tree worm is very vibrant in color and changes its color based on depth, camouflage, and a scare tactic.^[5] It has bright spiral rings around its body segments or radioles, which can number more than 200 segments.^[6] The body is abnormally large, ranging up to 45 mm (1.8 in) long and 0.5 mm (0.020 in) wide.^[6]

Biology

The species predominantly engages in reproduction throughout its lifespan. Males use their coloration to attract females.^[5] During mating, females emit a pheromone that signals males to release sperm. In turn, females release eggs; this action is called spawning.^[7] Larvae are characterized by an elongated body.^[8] The species also uses its color to make predators second guess their meal. The species primarily consumes suspended food particles, phytoplankton, and microalgae.^[5]

Distribution and habitat

Spirobranchus corniculatus can be found in the tropical Indo-Pacific, specifically in corals such as Porites lobata, which are typically found in Hawaiian waters.^[6] The Christmas tree worm inhabits depths of 3–30 m (9.8–98.4 ft)^[8] and can also be found living on almost every species of coral.^[5] It is mostly encountered in the eastern side of the globe, spanning Southeast Asia, the Indian Ocean, the central Pacific, and the northern region of Australia.^[5]

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