Periwinkle Snail and European Greencrab. The ascent of a thin spiral is enveloped by pressure. Morphed in the grip of an alien predator, the shell is compressed and thickened into a bastion from shattering. Surface and texture adjust accordingly to the dilation of an aperture. The circle informs the line as the spiral descends. A primordial form evolves in response to the strength of an external organism.