Plankton provide the foundation for life on earth. To advance our understanding of the marine ecosystem, for scientific, commercial and survival purposes, more in situ continuous monitoring and analysis of plankton is required. Cost, complexity, power and data communication demands are barriers to widespread deployment of in situ plankton microscopes. We address these barriers by building and characterizing a lensless microscope with a data pipeline optimized for the Raspberry Pi 3. The pipeline records 1080p video of multiple plankton swimming in a sample well while simultaneously detecting, tracking and selecting salient cropped images for classification @ 5.1 frames per second. Thirteen machine learning classifiers and combinations of nine sets of features are evaluated on nine plankton classes, optimized for speed (F1=0.74 @ 1 msec. per image prediction) and accuracy (F1=0.81 @ .80 sec.). System performance results confirm that performing the entire data pipeline from image capture to classification is possible on a low-cost open-source embedded computer.