23-08-26 Raw data for 4 taxa of melanopsids - distance travelled by shell - rod - magnet assembly

The aperture of the shell was sealed with a thin film of general-purpose waterproof glue and the shell was then attached by a hot-glue gun to the end of a fibre-glass rod (2 mm diameter) with the main whorl pointing upstream (‘head-upstream’). The resistance to water flow offered by the shell caused this assembly of shell, rod and magnet to be pushed towards a larger fixed magnet which resisted the deflection of the rod assembly. The shell was held in a tube 0.03m internal diameter and 30mm from the point at which the tube discharged into a test chamber. We focussed on empty shells to avoid the influence of biological behaviour, and we did not attempt to position the shell close to a surface. the shell assembly was in place, the gate valve was opened in steps. At each step, a measurement was made when the shell had stopped moving and was in a stable position. The water velocity was calculated by measuring the volume of the discharge from the pipe over a known period. All results were analysed after subtracting the response of the rod alone. For each shell measured in flowing water in the apparatus, a mean deflection from three replicated readings was obtained. When flow rates were reduced, the assembly moved firmly back to its original position; there was no indication that there was an issue of friction of the rod in its holding tube.