Whirlpool Pukai

The whirlpool pukai's tail functions as a buoy. It is filled with buoyant gases, including the very smelly methanethiol. While the smelliness of the gas is merely a byproduct of its digestive system, it does discourage predators from biting the whirlpool pukai's tail.

The buoyant tail, along with tiny air spaces in layers of its body wall, help it remain on the surface of the water. This allows it to fulfill the distinct niche of a sedentary, surface-dwelling filter-feeder. A whirlpool pukai feeds much like humans breathe: its stomach expands and contracts to create a difference in pressure relative to the environment. When the plankton-filled water flows in, the plankton are trapped inside the stomach by a combination of sticky mucus and microscopic "pincers" on the microvilli. The water swiftly passes through and is "exhaled" at the other end through a conical sphincter at the tip of the whirlpool pukai's tail.

To allow for constant water flow, the plankton are digested individually, rather than as a whole. Like the tentacles of a sundew, the microvilli will curl around a prey item to expose it to as many digestive glands as possible. The microvilli will inflate with fluids and join together with a thick mucus, creating a tiny dome or "mini-stomach." The chyme (semifluid mass of partly digested food) collects in an elastic, urn-shaped membrane outside the stomach, which drains to a "chyme pipe" in the thick part of the tail. The chyme pipe secretes a few enzymes on the chyme as the chyme passes to the coil of intestines lower on the tail. There, the food's nutrients are absorbed, and the lighter-than-air gases produced are shunted off to flotation chambers. (the "fins" on the tail) The heavier-than-air gases and indigestible solids are removed by water that flows in from the mouth, down a tail "pipe", and into the small waste storage area.

Despite its rocky-looking appearance, the whirlpool pukai's body segments are flexible, and can expand to accommodate water or especially big plankton. (that is, "especially big" relative to itself)