Worms may be fairly low on most reef visitors’ bucket lists but they’re super-important members of the reef environment. Overwhelmingly Polychaetes – that is, segmented worms lined with little limb-like appendages – they’re key prey in the marine food web and themselves important consumers of organic debris in the sediments.
FOR OUR PURPOSES – THAT IS, FOR SEEING THE REEF – marine worms come in three categories:
- The flashy tube worms we see all the time – like the Christmas Tree and feather duster worms that embed themselves in the corals and sea floor and extend their colorful tentacles into the water column to capture plankton;
- The sneaky guys we see sometimes – like the fireworms, scale, ribbon and flatworms that hide under rocks and crawl among the corals, and the Spaghetti Worms that stretch their tentacles across the substrate from hidey holes and crevices;
- The generally wormy worms we seldom see – like the lugworms and peanut worms that hide out in pretty much every square inch of sand flats and sediment.
Note: These are not exactly the criteria used by science, which classifies worms into phyla, families, genera and species based on actual physical characteristics and relationships. Here, we’re focused on the wormy critters we’re likely to encounter and how we’re likely to do so.
SEGMENTS, PARAPODS, SETAE – THE STUFF OF POLYCHATES
Most of the marine worms in our sights are members of Phylum Annelida (from “little rings”), known in street talk as segmented worms. Their bodies are made up of multiple ring-like segments, each with its own set of identical organs.
In the ocean world, the great preponderance of segmented worms, both in species and physical volume, are members of Class Polychaetea, a term meaning “many hairs.”
In these guys, first of all, each body segment sports a pair of parapodia, limb-like appendages used for walking, swimming and digging. Parapodia shapes reflect lifestyles – e.g.: leg-like, paddle-like, shovel-like.
And in nearly all species, each parapod is festooned with multitudinous spiny setae, or sort of haur-like bristles (the “chaetae” in polychaete).
Virtually all species sport setae/ bristles, but the term “bristle worm” is usually reserved for guys like fireworms. Not only do their particularly stiff bristles easily penetrate tissues (like fish mouths and human skin), they inject a stinging toxin that gives them their fiery reputations.
TUBE WORMS – GORGEOUS RADIOLES
Both Christmas Tree and feather duster worms live in cylindrical dwellings they construct, embedded in the corals or sediments.
Both extend their paired crowns of colorful radioles, specialized tentacles that filter plankton from the surrounding waters. The radioles can exhibit any of a range of colors but the colors don’t appear to serve any meaningful advantage. The radioles are coated with sticky mucus that traps particles that contact them, passing them down cilia-lined grooves to the mouth at the crown base. They also work like “gills” to let the animals absorb oxygen.
But, to be clear, beneath their fancy headgear, tucked inside their cylindrical domiciles, tube worms possess basic wormy bodies. As good polychaetes, they’re equipped with parapodia that help them move up and down inside their tubes. Additionally, the worms fan the parapodia to circulate water for in-tube aeration.
TUBE WORM DISTINCTIONS
Christmas Trees are entirely found embedded in corals, in tubes constructed of calcium carbonate they secrete with special glands. They don’t bore into it. They settle on living coral and let it grow up around them.
And they’re apparently picky about the types of coral they’ll settle on. It’s estimated that they can live as long as 30 years, although a more typical lifespan is likely to be 10 to 20 years.
Feather dusters are found in corals but they may be just as happy on sandy bottoms. Rather than calcium-based tubes, theycreate parchment-like tubes of mucus, strengthened with bits of sand and shell.
For both groups of worms, those feathery whorls are attractive to predators hoping to pick off an easy snack, so the ability to quickly withdraw into a protective tube home is important their survival.
Christmas trees have the advantage of opercula, or trap doors they can snap shut above them, flush with the coral surface. Feather dusters lack these, and in fact their tubes often extend above the substrate even when they’ve withdrawn into them.
But both worms’ tubes are usually significantly longer than their inhabitants – typically 1½ inches for the worm, as long as 10 inches for the tube – giving them room to scoot down in.
THE OTHER GUYS (JUST A FEW)
BRISTLE WORMS/FIRE WORMS
Polychaetes par excellence, fireworms are the free-living wormy guys that get people most excited – after all, they move about on the corals, looking menacing. And they sting. Their stiff bristles cause significant pain just by penetrating soft tissues. And when they do so, they inject a toxin that inflames those tissues upon contact.
They’re not easily spotted. Usually hidden in crevices and under rubble during daylight hours, they emerge at night to feed on coral polyps, sea anemones and small crustaceans. Sometimes you can encounter them crawling amidst coral head crannies during the daytime.
SPAGHETTI WORMS
Found in tropical waters worldwide, Spaghetti Worms are polychaete tube worms without the fancy radioles. Their tubes are concoctions of sand and mucus, but you’re unlikely to see them – they’re adept at hiding out in crevices, crannies and other obscure places.
What you will see are their long, mucus-infused feeding tentacles extending across the bottom from their hiding places in coral, rocks or rubble. They’re not exactly exciting, but you’ll see them.
RIBBON WORMS
Ribbon Worms make up an estimated 1,200 species in Phylum Nemertea – totally seperate from polychaetes. Found in in oceans worldwide, they’re thin, flattened unsegmented and often colorful.
They’re also excellent at hiding, spending their lives concealed in algae, crevices and rubble dining on invertebrates. In other words, rarely spotted.
MARINE FLATWORMS
With some 30,000 species in Phylum Platyhelminthes in Phylum Platyhelminthes (broad flat worms), Marine Flat Worms are broad, very thin and unsegmented.
And, often, very colorful – they’ve been called “butterflies of the sea.” They’re also hard to spot. They’re small, ranging in size, say, .004 of an inch to a few inches. Many hide out in crevices or under rocks, emerging only at nighttime.
But some do strut around in daylight. Their colors advertise a toxicity that makes them unattractive to predators. Others simply fake the toxicity, mimicking the nudibranchs they superficially resemble that are, in fact, toxic.
BURROWING WORMS
Burrowers like lugworms, acorn worms and peanut worms are not among the wormy critters you’re likely to encounter directly – and probably won’t be thrilled at if you do – but their importance can’t be overstated.
- First, they’re keystones of the food web. When bottom-feeding fish like rays and grunts scrounge in the sediments for edibles, it’s worms they’re after as well as crustaceans and small mollusks.
- Secondly, many are deposit feeders who swallow their way through sand and mud to extract nutrients, recycling them and contributing to healthy reef habitats. Others show up to break down animal carcasses or prey on other small invertebrates.
Many are polychaetes, many are in other phyla. Southern Lugworms (Arenicola cristata, Phylum Annelida), acorn worms (Phylum Hemichordata) and peanut worms (Phylum Sipuncula) are common representative types.
If you don’t see the worms themselves, sometimes you’ll see their signs. Lugworms and acorn worms both live in u-shaped burrows, ingesting sand for its nutrients and expelling the sandy waste as conical mounds or conical castings surrounding their burrow openings.
PRINCIPAL SOURCES: Reef Creature Identification Florida, Caribbean, Bahamas, Paul Humann, Ned DeLoach; Les Wilk; Reef Creature Identification, Tropical Pacific, Paul Humann, Ned DeLoach; Marine Life, Caribbean, Bahamas, Florida, Marty Snyderman & Clay Wiseman; Marine Life of the North Atlantic, Andrew Martinez; Why should we care about marine worms?, National Wildlife Foundation; What are Christmas tree worms? National Oceanic and Atmospheric Administration: Learn About the Life and Times of the Christmas Tree Worm, Thought.co.; Christmas Tree Worm, Oceana.org; Featherduster Worms, Waikiki Aquarium; Feather duster worm, Marine Education Society of Australasia; Giant Feather Duster Worms, Marinebio.org; Bristle Worms – Fireworms – Polychaete, ARC REEF (Atlantic Reef Conservation); Bristle Worms | Stinging Facts About Bearded Fireworms, PrivateScuba.com; Beautiful fireworm, Wild Singapore; Ocean Beauties: Marine Flatworms, Scuba.com; Spaghetti Worms, Waikiki Aquarium; Marine Worms, Annelid, et.all, Wikipedia.