This paper proposes a novel, lightweight deep convolutional neural network specifically designed for iris segmentation of noisy images acquired by mobile devices. Unlike previous studies, which only focused on improving the accuracy of segmentation mask using the popular CNN technology, our method is a complete end-to-end iris segmentation solution, i.e., segmentation mask and parameterized pupillary and limbic boundaries of the iris are obtained simultaneously, which further enables CNN-based iris segmentation to be applied in any regular iris recognition systems. By introducing an intermediate pictorial boundary representation, predictions of iris boundaries and segmentation mask have collectively formed a multi-label semantic segmentation problem, which could be well solved by a carefully adapted stacked hourglass network. Experimental results show that our method achieves competitive or state-of-the-art performance in both iris segmentation and localization on two challenging mobile iris databases.