It is aJapanese maple - acer palmatum, dissectum variety. They make excellent bonsai, with the caveat that most dissectums are grafted, which often makes for trunks with different coloured bark above and below the graft. You can collect disectum seed in late autumn and grow them on. In 10 years you will have lovely bonsai with no graft lines on the trunk. Some of the seedlings will be weak growers, others will be fine on their own roots.