Lagenorhynchus is, of course, the latin for dolphin. The idea of dolphins morphing into people came basically from the legend that is mentioned in the story about dolphins being the souls of dead sailors. I developed that into the idea that they did have a Human-like form. And from there the idea of a people who could be both humanoid and water-dwelling mammals was created. It only remained to create a planet for them to live on. One that was almost entirely water. Naturally that would attract the crew of the TARDIS.

The method of reaching the underwater city was a little problematic. In the real world the ‘bends’ would be an issue and the compression stops Chrístõ worries about would be necessary. But this is science fiction.

The underwater city, of course, owes its origins to many such ideas in fiction. Various 1950s/60s undersea city movies, an old episode of Doctor Who itself that featured the lost Atlantis, the modern Stargate Atlantis with its shield, though none of them were actually the inspiration for this city. It was thought out entirely from scratch. The style of the houses was kept simple, as was their life. The dolphin planet, which I later called Aquaria, is what was described in the episode Castrovalva as a ‘dwelling of simplicity’.

The simple life has a history, and that history is the main issue of the story. Tracing the origins of the dolphin people. The dead planet where their people come from, a desert with hardly any moisture in the air is a deliberate contrast to their own paradise. But the two main reasons for portraying them as colonists from another world are to allow for follow up stories in other settings and to put the idea that Earth dolphins might be related to these ones. Now eat a tuna sandwich if you can!