With only one trituration available, any provings or triturations of Urochordates would be of immense value. Since we have no provings of the Thaliaceae and Larvaceae, they would be a higher priority. A number of species are quite prominent as well, and would make excellent candidates for a proving.
Edible species of Tunicate, such as Halocynthia roretzi, Styela clava, Microcosmus sabatieri, Pyura chilensis, or Pyura praeputialis would make excellent choices for proving.
Several Tunicates have become invasive species over time in a number of geographic areas, such as the Didemnum and Styela genii. Didemnum vexillum has become smothering in the Georges Bank of North America, likely presenting a profound resonance to issues affecting this region.
Image Credit: https://en.wikipedia.org/wiki/Tunicate#/media/File:Ascidians.jpg