The body of the parchment tube worm, Chaetopterus variopedatus, is divided into three sections (Voss 1976). The anterior end is a combination of bristle-bearing segments and a shovel-like mouth. Paddle-like structures are found on the middle segment, which are used for pumping water through the subsurface tube. Finally, the body tapers through a series of segments toward the posterior section. The color of C. variopedatus is cream to pale pinkish, and the animal is capable of emitting intense bioluminescent flashes in response to external stimuli (see ‘Community Ecology’ below for more information).
The worm usually remains burrowed beneath the sediment in its U-shaped tube, composed of a parchment-like material imbedded with sand grains (Voss 1976). Both ends of the tube project about 10-13 cm above the sediment surface, like tapering chimneys. Tubes can be seen washed ashore on nearby beaches after strong storms.
Potentially Misidentified Species
Several polychaetes are found in the sediments of the IRL, and some species construct tubes using various materials. However, the parchment tube worm can be distinguished from similar species mainly by the appearance and height of the tube openings that rise well above the surrounding sediment (Voss 1980).
HABITAT AND DISTRIBUTION
The parchment tube worm is considered a cosmopolitan species, occurring in shallow coastal habitats in temperate to tropical locations worldwide (e.g. Gray 1961; Schaffner 1990; Hsueh & Huang 1998). Worm tubes are generally found partially buried on shallow sand or mud flats, or on protected beaches around the low-tide line. The majority of the U-shaped tube is submerged in the surrounding sediment at depths up to 15 cm (Schaffner 1990).
Few published reports are available concerning populations of C. variopedatus in the IRL, but worms can be found throughout the lagoon in the sediments of tidal flats and sheltered beaches.
LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan
The parchment tube worm typically grows to lengths of 14 to 24 cm, or greater (e.g. Macginitie 1939; Ruppert & Barnes 1994). The tubes in which the worms live may measure up to 85 cm in length, with a diameter of 4 cm at the widest middle portion (Gray 1961). As the worm grows, it cuts a slit in the tube with spines located on one of its segments, and then adds more material to expand both the length and width of the tube (Fauchald & Jumars 1979). The lifespan of C. variopedatus varies with environmental conditions and other factors, but most specimens that have been studied live for a period of about one year or less (Thompson & Schaffner 2001).
Details on the abundance of C. variopedatus in the IRL are scarce, but densities of over 1000 individuals m-2 were found for worm populations in the lower Chesapeake Bay at the height of the summer recruitment season (Thompson & Schaffner 2001). In other months, densities of about 30 to 60 individuals m-2 are more common (Schaffner 1990; Thompson & Schaffner 2001).
Reproduction & Embryology
Little information is available detailing the reproductive process for C. variopedatus. However, studies have shown that ovigerous females carry 150,000 to over one million eggs at a time (Thompson & Schaffner 2001). Spawning occurs in the summer for populations residing in Chesapeake Bay (Thompson & Schaffner 2001), but it is likely that the reproductive season of Florida populations is extended due to the warm temperate to subtropical climate. Larvae are planktonic, drifting and feeding in the water column before settling and building a permanent tube in the benthos (Fauchald & Jumars 1979).
Based on its range, the parchment tube worm likely prefers and/or requires warmer temperate to tropical waters in order to thrive.
Parchment tube worms can be found in a variety of salinities, from brackish estuaries to coastal marine waters.
Some studies refer to parchment tube worms as filter feeders, while others assign the species to the ‘suspension feeder’ category. The method of food collection in C. variopedatus differs from that of other filter feeders. In order to draw clean water through the tube, remove wastes, and pump in planktonic food, the worm beats a series of three modified paddle-like body segments (notopodia) against the inner wall of the tube (Macginitie 1939; Wells & Dales 1951; Brown 1975; Fauchald & Jumars 1979; Ruppert & Barnes 1994). This motion creates flow that pulls water into the anterior opening of the U-shaped tube and pushes it out through the opposing end. A mucous film is secreted between the notopodia, which curves to form a bag-like filter that traps detritus and planktonic organisms such as diatoms, protozoans, and larger metazoan zooplankton (Fauchald & Jumars 1979). When the bag reaches a certain size, it is detached from the notopodia, rolled into a ball and carried to the mouth for consumption. The entire process may occur quite rapidly, depending on the size of the worm and the amount of suspended material entering the tube. A worm measuring 18 to 24 cm in length may produce a mucous film at a rate of 1 mm per second, forming individual food balls up to 3 mm in diameter (Ruppert & Barnes 1994).
Little information is available detailing the predators of the parchment tube worm, but it is likely that C. variopedatus is preyed upon by a variety of large bottom-feeding fishes and crustaceans.
Like many other sedentary marine organisms that cannot readily retreat, C. variopedatus has evolved some complex anti-predatory strategies. Chaetopterus is one of a few genera of polychaetes with separate specialized regions that can regenerate an entire body from a single segment (Ruppert & Barnes 1994). Overall, this ability is more common among worms with undifferentiated trunks. Following predation of one or more body parts, the remaining segment(s) supply the cells for the regeneration of other segments, appendages, and even the head in some instances. In order to deter a potential predator before an attack takes place, the parchment tube worm also has the ability to luminesce, or emit bright clouds of luminescent mucous from its tube (Martin & Anctil 1984).
Parchment tube worms often share their borrows with a variety of organisms, including the commensal crabs, Pinnixa chaetopterana, Polyonyx gibbesi and P. bella (Gray 1961; Grove & Woodin 1996; Hsueh & Huang 1998; Grove et al. 2000). All these species likely gain considerable protection and food from the host worm, although some species are considered obligate associates; while others are facultative, choosing to live in association with the worm (Gray 1961).
In recent years, a compound called CVL has been isolated from the tissues of C. variopedatus and studied for its anti-HIV-1 activity (Wang et al. 2006). However, it is unknown whether the compound will reach large-scale synthesis or medical trial stages.
C. variopedatus is considered an ecologically important species for two reasons. First, the worm cycles nutrients by transforming suspended detritus into benthic organic matter through filtration and defecation (Thompson & Schaffner). Secondly, the presence of worm tubes in sediments has been shown to increase benthic biodiversity, presumably because several organisms live on and around the tube openings (Schaffner 1990).
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