Translume will develop an extremely robust, inexpensive micro flow cytometer (mFCM) for quantitative detection of phytoplankton. This device will be designed to be deployed on oceanographic platforms, such as moored buoys, or autonomous vehicles of the type presently used by our collaborator Dr. Needoba at the NSF Center for Coastal Margin Observation and Prediction. Our microflow cytomer will be optimized for low power consumption and autonomous long-endurance operations. Previous flow cytometers designed for at-sea applications are physically large and have considerable consumable needs. While the core of these instruments may be small, they require ancillary systems that drastically increase their size, weight, and power consumption. In order to reduce size and power consumption, our mFCM will operate without any pump. We will rely on sea motion (either waves or motion of the vehicle) to drive the fluid (sample and sheath) through our cytometer. The flow velocity will be unsteady and at times may be severely pulsed. This mode of operation would normally be considered unacceptable, as it would drastically affect the flow characteristics such as sheathing, as well as phytoplankton size and density measurements. However, our device will include an integrated optical flow velocity measurement capability that will remediate these shortcomings. The complexity associated with this velocity measurement capability, and the related power consumption, is only a small fraction of that of a pump-operated system. Thus the practical challenges of oceanic deployments will be significantly reduced. Expenditure of sheathing fluid will be minimized using advanced three-dimensional microfluidic design features; or potentially completely eliminated using a sheath-less design. Extreme robustness will be insured by creating all elements (microfluidic optics, structural frame) in a single fused silica monolith providing permanent and exact alignment of all elements.