Dataset: Microsphere counts from Oikopleura dioica houses following feeding incubations with two microsphere sizes (for each functionalized microsphere) available in equal concentration.

Experiments with 5-day old O. dioica were conducted at the Michael Sars Centre in Bergen, Norway in October 2022 and 2023. Individual animals (15-24 replicates) were removed from their culture chamber, probed to abandon their house, and placed in a staging beaker containing 0.22 µm filtered seawater (FSW) to build fresh houses. Up to 12 actively pumping animals were then transferred from the staging beaker to an incubation chamber. Feeding incubations were carried out in a 12˚C water table with a motorized stir paddle to maintain suspension for 10 minutes. Following the 10-minute incubation, 3-8 animals were individually pipetted into watch glasses and probed to abandon houses so that the appendicularian and house could be preserved separately. Appendicularians were fixed by pipetting animal in 1 mL FSW into a 1.8 mL cryovial with 5 µl 25% microscopy grade glutaraldehyde (0.125% final concentration) to stop digestion. Houses were pipetted into cryovials in a volume of 100 µl without fixative.

Laboratory feeding incubations were carried out on two occasions with two experimental designs. One with all particle sizes (1.0 and 2.0 µm) available in equal concentration to appendicularians. The other with particle sizes (0.5, 1.0 and 3.0 µm) simulated environmental conditions with smaller particles available in higher concentration. For each particle size, two different microsphere types were used with different functionalized surfaces (carboxylate- and amine-modified).