Spirobranchus giganteus

Spirobranchus giganteus is a tubicolous annelid that shares the Serpulidae family with about 300 other species. Specimens of Spirobranchus giganteus are found in a wide range of depths, from shallow waters to several hundred meters deep. In terms of geographic distribution, they inhabit the tropical waters of the Pacific, Atlantic, Red Sea, Mediterranean and Caribbean oceans.

This colorful species is accustomed to enter live corals (especially of the Porites genus), as well as dead corals, bivalve shells or even wood, from which only two tentacular crowns show outwards, which can have very bright and varied colors. These tentacular crowns are each formed by a spiral of feathery filaments called radioles, which have two main functions. On the one hand, they capture, thanks to a sticky substance that coats them, the food they filter from the water column. The second function of the radioles is that being vascuralized, they allow them to carry out the gas exchange with the water, and therefore serve the specimen to breathe. At the slightest threat felt by the specimen (they are very sensitive to changes in pressure and light), it will completely retract its crowns into the tube, closing the opening with an modified radiole in the form of a calcareous operculum.

The total length of Spirobranchus giganteus can reach 10 cm, although only a few centimeters of the animal will be visible to the observer. The length of the calcareous tube they form is longer than the length of the animal itself.

As for the reproduction of Spirobranchus giganteus, it is a species with separate sexes (dioecious) whose specimens release eggs and sperm into the water column. There, fertilization will take place, generating larvae that will remain part of the plankton for several weeks. After this time, and after being dispersed by the dominant currents in the area, the larvae settle to the bottom to develop into adults.