11 May 2010

The platanna: a flat frog with many dimensions

Camilla Bath
Common platanna

This slippery frog may look unassuming, with its tapering, flattened body, muted colours and small, pointed head, but it’s actually one of the most fascinating. For instance, it’s possibly the only frog that can hop backwards – on land, or in water!

The platanna’s common English name comes from the Dutch word, plathander, which means “flat-handed creature”. This frog’s hands and feet also influenced the selection of its genus name, Xenopus. The Latin name, meaning “strange foot”, was given to the platanna because it has sharp back claws (probably used to rake up mud, or sand to use as camouflage) on only three of its toes.

Its fingers lack claws and webbing. This is one slippery character, thanks to its protective mucous covering and smooth skin.

There are 18 different species of platannas in sub-Saharan Africa, also collectively known as African clawed frogs. The best-known species is the common platanna (Xenopus laevis), which is often studied as a model organism.

The platanna’s genus name literally means “medical frog” in Hebrew and they are widely used in laboratory research. They have large cells that are easy for scientists to culture and use in experiments. In the early 1900s, platannas were used around the world as the only reliable pregnancy test available and this low-tech method is still used in some rural areas today. A female frog will spawn when injected with the urine of a pregnant woman, as a result of the high levels of the pregnancy hormone, human chorionic gonadotropin (hCG).

Platannas are also known as the tongueless frog, as they lack the long, sticky organ that most frogs use to catch their prey. Instead, platannas use their fingers to pick up food. They jerk their fork-like digits together to hold their food (usually small fish, crustaceans, insects, worms, or larvae) before clamping down on their prey with their mouths. The species’ tongue is completely attached to the floor of the mouth.

Platannas are excellent swimmers and spend most of their time in water. Their back legs are powerful, with long webbed toes. They are highly aquatic animals, perfectly adapted to moving quickly and with agility in water. These frogs live mainly in lakes, rivers, swamps and reservoirs – but they have been seen to migrate to other bodies of water during periods of drought. On land, the creatures become clumsy and awkward, moving in a series of flopping motions.

Another interesting fact about platannas is that they have no vocal sac; the only noise they can make is a clicking sound when they’re underwater. What’s more, their eyelids and eardrums are both immovable.

You can spot these fascinating aquatic creatures in the Aquarium’s Frogs: Beyond the Pond exhibit.

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