A cat carrier includes a tray, and an enclosure formed of: a lower housing portion with an upper mating flange, and an upper housing portion with a lower mating flange. Protrusions on one mating flange slidably engage openings formed with respect to the other mating flange, to releasably couple the housings together without tools. Holes in each of the mating flanges align, when the housing portions are mated, and each aligned pair of holes receives a fastener to releasably secure the housing portions together. The holes on one flange transition into a keyed opening (e.g. a hexagonal-shaped opening) that receives a hex head of a bolt, to prevent rotation of the bolt when a wing nut is tightened onto the fastener, permitting final assembly without the use of tools. The protrusions create a gap between the flanges, forming a track, which receives/guides a flange of the base.