|One of the caecilian species in the Order Gymnophiona|
One rather remarkable characteristic that these animals exhibit is that mothers feed their young. This feeding is very unusual in the animal kingdom, though, in that mothers develop tissue inside of the oviduct for this purpose. Early on, eggs develop as normal, with the offspring feeding on the yolk. However, after this food supply is gone the offspring break out and then latch onto their mother's oviduct tissue. The tissue releases a milk-like substance specifically produced for feeding the young, but the babies also take chunks out of the tissue as they feed. Other species have an even more bizarre method in which the young scrape the skin off of their mother's body. Caecilians are also unusual among amphibians in that fertilization is internal.
Below is a video depicting these unusual creatures and some of their habits, narrated by the ever-wonderful David Attenborough. Discussion of Caecilians begins at 0:24.
Sources are the San Diego Zoo, Animal Diversity Web, and Vertebrate Life. Image is from Wikimedia Commons under a Creative Commons license. Video is from YouTube.