23 Steromphala umbilicalis. H. 6mm, B.11.5mm. Aug. 2013. Menai Strait, Wales.

23 Steromphala umbilicalis. H. 6mm, B.11.5mm. Aug. 2013. Menai Strait, Wales.

Foot on glass. Travels with direct, ditaxic, compression waves (dark in image) on the sole. Turns by different rates (or reversal) of wave-flow on either side of central furrow.