How do gastropods grow synchronized shell sculpture? Effect of experimental varix manipulations on shell growth byCeratostoma foliatum(Muricidae: Ocenebrinae)

Abstract

Gastropod shells display striking patterns in both color and sculpture, but rather little is known about the developmental mechanisms that produce those patterns. Here, we tested a physical feedback hypothesis for how snails control spatial patterning of shell sculpture. Varices—a form of synchronized, blade‐like axial sculpture—are produced at regular intervals around the shell and often aligned closely between adjacent whorls. Older varices were believed to provide a spatial cue about where to position a new varix. To test this hypothesis, we manipulated physical cues by cutting off varices or attaching new ones to the body whorl of individuals of Ceratostoma foliatum, and then allowing snails to grow a new varix. We found that previous varices on the shell were neither necessary nor sufficient to induce a new varix at a particular location. However, the position of older varices did appear to affect the fine tuning of subsequent varix placement. The results of our experiments therefore suggest that varix synchrony arises mainly from some internal mechanism that yields a standardized amount of spiral growth per growth spurt. We also found that shell damage can induce varix production in unusual or aberrant locations during subsequent shell growth.

Quantitative measures and 3D shell models reveal interactions between bands and their position on growing snail shells

“…It should be noted also that physical cues in marine gastropod shells possessing varices (thickened protrusions of shell) do not appear to be the main mechanism used to position new shell structures. Instead, it has been suggested that positional information of these structures is created by a Turinglike system, but with previous shell structures providing some finetuning feedback (Webster & Palmer, 2019).…”

Overcoming the constraints of spiral growth: the case of shell remodelling

“…In dextrally coiled univalved shells, the left side of the mantle (on the inner‐lip or columellar side) dissolves skeletal material on the outer shell surface as the edge of the inner lip expands over the exposed whorl during spiral growth. As a result, external sculpture is partially or wholly removed before the surface is glazed over by the mantle or foot epithelium (Carriker 1972; Webster & Palmer 2019). This kind of surficial dissolution is widespread in gastropods (Signor 1982) and coiled shell‐bearing cephalopods (Signor 1985; Radtke et al .…”