Estimating the Retraction Force of a Radiolarian Axial Projection: A Case of Eucyrtidium hexastichum (Haeckel)

Abstract

We report on a process for estimating the retraction force of a pseudopodium of a radiolarian specimen using a video recording of its behavior. Specifically, we focused on the retraction of the axial projection, which is the longest and the thickest pseudopodium, using the video recording of the movement of the specimen towards the container bottom to which its axial projection tip had adhered. Our approach consisted of three steps: shape approximation using seventh-order polynomials, estimation of the movement speed, and numerical simulation of the fluid flow around an object with the same shape as the specimen. The retraction force was estimated to be approximately 2.22 × 10⁻¹⁰ N.