From: Brighton, UK
In my own custom mod I added 'Aquatic'. The Wekkarus and Lemeresh (the latter from DWE) are currently the only two races set as this. For the biases I think I went for a slightly more extreme level than those of the Amphibious family.
I added 'Arachnid' just for the Dhayuts, to try and break up the Insectoid monolith somewhat! Almost every family dislikes Arachnids, as spiders traditionally feed on everything they are big enough to eat, that is except Machine races.
With regard to the game's use of 'Ursidian' as a family, though this does actually mean 'bear-like', I think DW uses it more simply to refer to 'animalistic' races not small enough to be considered Rodents. As such I changed the Zenox to Ursidian. I guess you could break this up further, into actual Ursine, Canine, Feline, etc... races if you wanted, but I'm only playing with the 40 races of DWE and the catch-all use of Ursidian works well for me. I remember in the Ikkaru Galactopedia descrition it says they are a 'primate' race, which of course the humans are as well, so I think I changed just that word to 'simian', which in the context of the game I took to mean 'monkey-like'.
Perhaps it would be great if in further patches to the game some more complexity was added to raceFamilies.txt, allowing for further definition of the differences between familes? Other, that is, than just how much the like/dislike each other, and how the Shakturi feel toward them.
I toyed a while back with the idea of dividing the Reptilians into 'Saurian' (I think I would have put the Naxxilians and the Mortalens in that group... but I'm not sure now) and something approximating as 'lizard-like', but I couldn't find an appropriately technical word for that latter category. The Reptilians are the largest grouping in the vanilla game it makes a lot of sense to try and divide them up somewhat.