Relating ciliary propulsion morphology and flow to particle acquisition in marine planktonic ciliates I: the tintinnid ciliate Amphorides quadrilineata.

This article focuses on the feeding-current generation and particle handling behaviors of the marine tintinnid ciliate *Amphorides quadrilineata*. Using high-speed digital imaging, micro-particle image velocimetry (μPIV), and computational fluid dynamics (CFD), the study demonstrates that *A. quadrilineata* swims forward by beating its oral cilia backward, creating a feeding current characterized by a saddle flow vector field that laterally directs particles to the ciliary ring for selective capture via localized ciliary reversals. When swimming backward, ciliary beating reverses, generating an inverse saddle flow that facilitates active rejection of unwanted particles. The lorica, a protective shell, increases drag and mechanical power requirements but enhances feeding-current generation and particle encounter rates through a drag-based mechanism, with CFD simulations estimating a ~29% higher encounter rate for cells with a full-length lorica compared to those without.