From TARDIS Index File, the free Doctor Who reference.

Chimeron
Place of origin:	Chumeria
Appearances:	DW: Delta and the Bannermen
Notable Individuals:	Delta

The Chimeron are a race of humanoids who were nearly wiped out.

Chimerons hatch from large grey eggs and start as green, wrinkly infants. Though males keep this appearance throughout their life, the queens of the species have a slightly different development. In order to properly develop, the young queens are given a special substance from birth onwards. In the first few hours, they rapidly grow and become more Human-like, developing hair and other more distinct facial features and they start losing wrinkles. Chimeron queens also develop a strong singing voice at this age, partly as communication and partly as a powerful means of defence. Once they reach the Singing Time, they perfect their defensive songs and reach closer to adult size. Adult queen chimerons look similar to Human females with slightly green skin and grey patches behind the ears for detecting higher frequencies.

The Chimerons were nearly wiped out by the Bannermen, but one of the last queens, Delta, was able to escape with an egg. The egg hatched on Earth, and with the assistance of the Doctor, Delta and her daughter were able to escape annihilation by the Bannermen; they eventually left earth in the company of a young human named Billy who had fallen in love with Delta and took a serum (actually Chimeron baby food) that began to transform him into a Chimeron. (DW: Delta and the Bannermen)