How do snails grow complex shells?


Photos courtesy of Wiley Online Library

Many marine snails produce breathtakingly beautiful shells, where pronounced shell sculpture — like rows of spines or broad flattened blades (called varices) — are aligned between one turn of the shell and the next. As a snail adds new shell at the aperture (the main opening of the shell) during growth, new varices are typically aligned with older varices to yield a surprisingly regular pattern. However, how snails control the placement of new sculpture when they grow, has long puzzled biologists.

University of Alberta researchers, Dr. Nicole Webster and Dr. Richard Palmer used manipulative experiments conducted at BMSC to test how new varices are positioned on the shell during growth of one of the most beautiful shells in the northeastern Pacific: the marine snail Ceratostoma foliatum. Varices were experimentally removed, or experimentally added at unexpected places on the shell, and the snails were then grown under controlled conditions to see how varix removal or re-positioning affected the placement of new varices during subsequent growth. Surprisingly, these experiments did not provide strong support for the widely-held hypothesis that physical contact with a pre-existing varix triggers production of a new varix during growth. Instead, the authors suggest that varix synchrony and spacing may arise from an intrinsic clock-like mechanism that can be further influenced by shell damage and repair. These are also experiments that can really only be done reliably at a research facility like BMSC, with an excellent running seawater system and ready access to the field for experimental animals and their natural prey (Photograph by N. Webster)

Webster, Nicole and A. Richard Palmer, 2019. How do gastropods grow synchronized shell sculpture? Effect of experimental varix manipulations on shell growth by Ceratostoma foliatum (Muricidae: Ocenebrinae). Invertebrate Biology 138:74–88.