We report the generation of subdiffractive laser light focal spots in far-field regime, by means of the so-called Optical Eigenmodes (OEi) technique applied to the focusing properties of a single valve of Arachnoidiscus genus diatom. Diatoms are ubiquitous microalgae whose external walls are able to confine light in several hot-spots. We demonstrated that the presence of the valve brings a significant contribution to the OEi-induced light squeezing, improving its performance.