A tidy white archival cardboard box is filled with what looks rather like tiny stone churros, barely a few centimeters long. These are fossilized tubes that once housed marine polychaete worms. Also amongst this gathering are elegantly curved tubes with distinctive thin flanges or wings.
The old handwritten label identifies the contents as “Hamulus onyx” (now recognized under the name Pyrgopolon onyx), which applies to the churro-like tubes with their longitudinal grooves. The winged tubes most likely belonged to a closely related species, H. squamosus. The label indicates the fossils were found in Cretaceous age deposits along the Tombigbee River that straddles the states of Mississippi and Alabama.
Hamulus is a genus of serpulid polychaete worms. Being soft-bodied, worms seldom leave a trace in the fossil record; however, some polychaetes build tubes of mucous, chiton, calcium carbonate, or agglomerated sand/random particles of stuff. Serpulid worms specialize in secreting protective hard calcium carbonate tubes around them, which are then more likely to survive the fossilization process even if the worms themselves vanish. As a result, we know that this is an extremely ancient group of animals, with the first unequivocal fossils dating from the Middle Triassic, about 244 million years ago. Serpulids still exist today, encrusting hard substrates at all depths in the world’s oceans.
While we may think of worms of the earth as force of decomposition, the serpulids are builders that have contributed to the construction of mounds and reefs for millions of years. But like other marine animals that biomineralize calcium carbonate, the serpulids’ stony shelters are in danger from the dissolving effects of ocean acidification caused by global carbon emissions. Though many species of serpulids remain abundant and are even deemed biofouling agents that encrust human-made structures, scientific studies show increased levels of dissolved carbon dioxide weakens the structure of worm tubes. What we learn from these little creatures informs us about the impacts we have on other organisms. And all organisms — even worms — deserve to have safe, strong homes.
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