''Odontosyllis phosphorea'', commonly known as a fireworm, is a

polychaete worm 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 ma ...

that inhabits the Pacific coast of North and Central America. The organism normally lives in a tube on the seabed, but it becomes

bioluminescent Bioluminescence is the emission of light during a chemiluminescence reaction by living organisms. Bioluminescence occurs in multifarious organisms ranging from marine vertebrates and invertebrates, as well as in some fungi, microorganisms inc ...

when it rises to the surface of the sea during breeding season.

Description

''Odontosyllis phosphorea'' is a small worm some long and in diameter when fully grown. Its elongated body is composed of many segments, each bearing a pair of

parapodia In invertebrates, the term parapodium ( Gr. ''para'', beyond or beside + ''podia'', feet; : parapodia) refers to lateral outgrowths or protrusions from the body. Parapodia are predominantly found in annelids, where they are paired, unjointed late ...

. With these appendages it can crawl, burrow and swim, but it normally lives in a parchment-like tube it creates on a rock or other hard surface on the

seabed The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as seabeds. The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...

. The head has two pairs of eyes, a nuchal hood which covers the back of the

prostomium The prostomium (From Ancient Greek, meaning "before the mouth"; : prostomia; sometimes also called the "acron") is the Cephalization, cephalized first body segment in an annelid worm's body at the anterior end. It is in front of (but does not in ...

, and a ring of small curved teeth inside the

pharynx The pharynx (: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea (the tubes going down to the stomach and the lungs respectively). It is found in vertebrates and invertebrates ...

. The parapodia in the central part of the body are slender and tapering. The upper surface of the worm is dark with yellowish transverse bands.

Distribution and habitat

This fireworm occurs on the west coast of North America from British Columbia to California, with a separate population off the coast of Panama in Central America. The species typically lives among seaweed growing on rocks and among seagrasses such as ''

Zostera ''Zostera'' is a small genus of widely distributed seagrasses, commonly called marine eelgrass, or simply seagrass or eelgrass. The genus ''Zostera'' contains 15 species. Ecology '' Zostera marina'' is found on sandy substrates or in estuarie ...

''. It can be found on the seabed from the

intertidal zone The intertidal zone or foreshore is the area above water level at low tide and underwater at high tide; in other words, it is the part of the littoral zone within the tidal range. This area can include several types of habitats with various ...

down to the

continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an islan ...

Ecology

''Odontosyllis phosphorea'' feeds mainly on

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

microalgae Microalgae or microphytes are microscopic scale, microscopic algae invisible to the naked eye. They are phytoplankton typically found in freshwater and marine life, marine systems, living in both the water column and sediment. They are unicellul ...

and

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

ic particles. It swallows this prey whole by everting its pharynx around the food item. It is itself eaten by fish, crabs and birds, being particularly vulnerable during its reproductive phase when it rises to the surface. One means of defence that it exhibits at these times is that it can shed its bioluminescent tail which may serve as a

decoy A decoy (derived from the Dutch ''de'' ''kooi'', literally "the cage" or possibly ''eenden kooi'', " duck cage") is usually a person, device, or event which resembles what an individual or a group might be looking for, but it is only meant to ...

while the worm returns to the seabed. Reproduction is seasonal in ''O. phosphorea'', its timing related to the phases of the moon. Spawning takes place between June and October, at night at two-weekly intervals coinciding with

neap tide Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables c ...

s. Shortly after sunset, worms begin to rise to the surface. Males usually appear first, the hind part of their body emitting a blue-green light, and periodically discharging a lingering secretion of luminous matter into the water. Females appear soon afterwards, emitting flashes of light, and swimming in small circles on the water's surface. Both the body of the female and the secretions it produces are luminous and sometimes a male gyrates on the surface with a female. The display ceases within half an hour of starting. Water samples taken in the vicinity of males and females and their luminous secretions contain spermatozoa and eggs respectively. This breeding activity contrasts with the closely related Bermuda fireworm (''Odontosyllis enopla'') which is largely non-seasonal in its breeding behaviour but very specific in its lunar periodicity and timing, rising to the surface to spawn 55 minutes after sunset, on a night just after the full moon.

References

{{Taxonbar, from=Q3525254 Syllidae Bioluminescent annelids Animals described in 1909