These tiny snails, their tubes are only 1-2 mm in diameter, superficially look like tube-dwelling worms. They feed by extruding a plankton-entrapping mucus net that they later can ingest. Note the operculum used to seal shut their tube.
Summary[edit] Description: English: Fossil of a Serpulorbis granifera at the Tellus Science Museum near Cartersville, Georgia. Date: 18 September 2021 (according to Exif data). Source: Own work. Author: JJonahJackalope.
Description: Petaloconchus sp. - beachworn worm shell mass, 3.05 cm across. Family Vermetidae - worm shells are filter-feeding, hard-substrate encrusters. Vermetid gastropods often encrust their shells together, resulting in irregular, twisted masses or small reef-like structures. Date: 16 March 2011, 20:13. Source: Petaloconchus sp. (worm shell) (San Salvador Island, Bahamas) 3. Author: James St. John.