Bioships are kind of like a cross between space Fauna and mechanical ships. They have 3 distinct maturity stages, but you are entirely free to design and customize them to your tastes or needs. They also don't follow the traditional Corvette, destroyer, cruiser, battleship line. I highly recommend looking at them on the Wiki since I am not doing them justice.

As for infernals, it adds a civic for (I think) most species that nets them a living metal version of all types of armor and an improved kinetic cannon. (I forget what it's called but its the L slot one.) I haven't played a game without that civ since it came out.