This figure is the Three-spined Stickleback (or Tiddler, or Tiddlebat, in Great Britain, because that’s kind of hilarious), Gasterosteus aculeatus, number 12 from the first series. This is the only representative of the stickleback order in the set; phylogenetically, they are grouped with more familiar spiny fish like scorpionfish, sea-robins and wolffish (at one time they were grouped with seahorses, pipefish and kin in Sygnathiformes, but that is no longer considered correct).