Fig. 2. Biomimetic tadpole robot (`Tadro') with biomimetic tail. Modeled after the free-swimming larvae of the sea squirts (subphylum Urochordata), the robots have a single eyespot (photoresistor), a flapping tail, and a microcontroller that converts the light intensity at the eyespot into a turning angle at the tail. This sensorimotor system produces autonomous phototactic navigation (Long, Jr et al., 2004b). New to this version of the Tadro are the digital microcontroller, servo tail flapper, and the biomimetic gelatin hydrogel of the tail serving as a notochord. The notochord's spring stiffness, k, is determined by bending modulus E and length L, which are coded as quantitative trait loci. The flapping amplitude of the servo motor was constant at ±30°. The tail position had a range of 180°. See Table 1 for additional operating and morphological parameters.