THE EFFECT OF SHELL MORPHOLOGY ON SEDIMENT RETENTION IN TURRITELLINE GASTROPODS

Turritelline gastropods are typically semi-infaunal, spending the majority of their lives in sediment with only their apertures exposed at the sediment-water interface. Species vary in both whorl profile and shell sculpture, which consists of varying numbers of fine to pronounced spiral chords, but the effect of these variations on sediment retention has not previously been analyzed.

In order to consistently compare a variety of morphologies we micro-CT scanned six extant and fossil species representing a variety of shell forms, Mesalia brevialis (Recent), Turritella abrupta (Miocene), T. acuticarinata, T. banksii (Recent), T. duplicata (Recent), and T. montanitensis (Miocene). These species range from straight-sided (T. banksii) to strongly convex (M. brevialis) in profile and from nearly smooth (T. banksii) to strongly bicarinate (acuticarinata). These digital models were cropped to 50 mm in length and 3D printed the models using an ObJetPro 3D printer using the polymer acrylic DurusWhite RGD525.

The printed models were placed in a flume with a small amount of the apertural end of the model exposed and the rest of the model buried 1 cm below the sediment water interface at the apical end. All models were tested in 2 natural sands, a fine sand (average particle diameter 0.25 mm), and a coarse sand (average diameter 1.5 mm). Photos were taken before and after 15 minutes of exposure to current and the additional area exposed was calculated. Each species-sediment size pair was tested multiple times. While all results appeared normally distributed, they were also highly variable for each species. Further, superior performance in a particular sediment type was not necessarily consistent with the habitat of that species. Additionally, sculpture complexity, measured as the trace of one side of a whorl divided by the height of that whorl, did not exhibit a strong relationship with sediment retention.