Brazilian dwarf arboreals that build trapdoors on tree bark, which is a combination nothing else in the hobby offers. T. seladonia is the famous one and it is genuinely spectacular in a way photographs undersell.
Tiny, under two inches, and it constructs a hinged silk and bark door on a vertical surface and lives behind it. Delicate, requiring specific ventilation and humidity, and unforgiving of husbandry errors.
Brazilian export is closed and breeding is difficult, so the supply chain is short, European, and prone to gaps. seladonia has been among the most expensive tarantulas in the hobby for years and has not followed the usual decline curve, because production has never scaled. This is one of the few cases where waiting for the price to fall has not worked.