A little Snakuscule snake snaked its way into Fiji! Amongst other plugins, the good people from the Biomedical Imaging Group of the EPFL in Switzerland kindly permitted us to redistribute the Snakuscule plugin!
After updating Fiji, you will find the menu item Plugins › Segmentation › Snakuscule. After clicking on it, you will see two concentric circles on your image – the Snakuscule. After putting it roughly into a place of a blob-like structure in your image, clicking on the optimization button in the toolbar will fit the Snakuscule to the structure in the image as well as possible.