Just turn your back, Mom.

A female in a species of legless amphibians called caecilians nourishes her youngsters by letting them eat the skin off her back, says an international research team.

Caecilians, which look like worms or snakes, burrow through the soil in the tropics. Some species lay eggs, and quirks of several of these species got Mark Wilkinson of the Natural History Museum in London and other researchers wondering whether these morns fed their young. The hatchlings had scraperlike teeth, for example, and they hung around their mother for their first weeks of life.

Now studying the egg-laying African species Boulengerula taitanus, Wilkinson and his colleagues have found the missing baby food. They dug up and observed 21 nesting females and their broods.

The researchers saw skinny, pink youngsters poke their lower jaws against their mother's' backs and peel off the dark outer layer of her skin, leaving her bluish white. Also, females with young develop an especially thick outer layer of skin with morsels of fat in it, the researchers report in the April 13 Nature.

The scraper teeth in these young resemble teeth of fetal caecilians in live-birth species. Scientists speculate that those youngsters use them to graze on the linings of their mothers' oviducts as they slide by. Since the skin feeders have the same kind of scraper teeth, researchers speculate they come from a lineage intermediate between ancient, egg-laying lineages of caecilians and more-recent lineages bearing live young.--S. M.