Comparative shell coiling and surface texture of Spirorbis species from the Devonian 插畫檔

This scientific illustration provides life-sized and magnified views of small calcareous tubes secreted by marine annelid worms during the Devonian period. The first figure displays a specimen found in both Europe and America, shown at its natural minute size and significantly enlarged to reveal its smooth, planispiral coiling reminiscent of a tiny snail shell. The second figure illustrates a different species from America, distinguished by its prominent, radiating surface ridges and a slightly more compact coil. A final view shows an individual of this same American species but with the tube twisted in the opposite or reverse direction, demonstrating the natural variation in coiling symmetry among these organisms. These tiny, coiled structures were typically found attached to the surfaces of shells, corals, or seaweeds in ancient shallow-water marine environments.