We sometimes hear that a platypus doesn't have a stomach. This statement presumably is based on a study published in 2008 about the genes controlling platypus digestion. The study's findings were summarised as signifying that "the platypus lacks a functional stomach".
However the platypus's digestive tract does include a small expanded pouch-like section where one would normally expect a stomach to be located.
Unlike a human stomach, this structure doesn't secrete digestive acids or enzymes, though it does contain Brunner's glands. This produces a mucus-rich fluid to assist nutrient absorption.
Given that platypus foraging behaviour entails swallowing relatively small mouthfuls of food at intervals of 40 seconds or generally longer over a feeding period lasting many hours, there's also no need for the animal's stomach to have a large holding capacity to accommodate large but occasional meals.
Related, is the story we hear that a platypus does not have teeth. They actually are born with teeth, but they shed them soon after they start eating solid food.
In the absence of teeth, it has sometimes been claimed that a platypus uses gravel to help mash its food into manageable pieces for consumption.
It would seem that platypus food is mashed up so well in the mouth that it's unnecessary for much additional processing to occur before food reaches the intestines.
Bits of mud and sand are sometimes found mixed with edible invertebrates when these are removed by researchers from a platypus's cheek pouches which they use to temporarily store prey while swimming underwater.
However, there's no reason to believe that this inedible material is anything other than an inconvenience, ingested accidentally as a platypus grabs its mainly bottom-dwelling prey.
After losing its teeth, the platypus chews up its prey using rough grinding pads located at the back of its jaws, probably after squeezing excess water out of its mouth through corrugations located at the edge of the lower bill.
The grinding pads are made of the tough structural protein called keratin. Keratin is also found in human hair and fingernails and the claws, horns and hooves of other mammals.
In a platypus's bill, it can reduce aquatic insects, small freshwater shrimps and worms to a fine paste without any help from other abrasive agents.
For more information about the platypus and its conservation needs, see the Australian Platypus Conservancy website at www.platypus.asn.au. You can also report any sightings of platypus (and rakali/the Australian water-rat) through this site.
- Melody Serena is a conservation biologist at Australian Platypus Conservancy.
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