Life

An amphibious wormlike creature has been found whose young feed on their mother's skin. Part of a group of tropical, legless amphibians called the caecilians, the creature may constitute a missing evolutionary link between hatching from eggs to the live births seen in modern mammals, the researchers believe.

Nursing mothers of Boulengerula taitanus transform the top layer of their skin from its usual flat, dead cells to a thicker layer of large cells rich in protein and fats. The nutrient content of this skin layer is similar to that of milk.

The infants hatch out of closely guarded eggs and are born with immature bodies. They are totally reliant on their mother for the first two months of life. They emerge with modified teeth that allow them to scrape off the top layer of their mother's skin, but they are unable to feed on termites or to dig in the soil until their adult teeth form. Click here to watch a video (wmv format) of a young worm feeding from its mother.

Internal hatching

Alex Kupfer at the Natural History Museum, London, UK, and colleagues discovered the extraordinary cannibalistic behaviour of these caecilians, which allows the young animal to increase its body length by 11% per week.

Caecilians have evolved a diverse range of birthing methods, which may illuminate evolutionary steps en route to the live births of today's mammals.

"About 30% of caecilians give birth to live young, which hatch out of eggs while inside the mother's oviducts and feed on her oviduct tissue before emerging as independent adults after 12 months' gestation. Other species of caecilian have a ‘marsupial' stage, while others hatch from eggs as adults," Kupfer told New Scientist.

Much is still unknown about this 150-million-year-old skin-feeding species and about caecilians in general, some of which can grow to more than 150 centimetres in length. It is not yet clear whether the variety of birth types seen in other land animals is evolutionarily related to caecilians or emerged through separate paths.

Journal reference: Nature (vol 440, p 926)

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