The larval stage of a creature's development is its earliest stage. Many insects have a larval stage, and the larvae can look very different to the adult of the same insect.
Something is long if it goes for a considerable way in one direction. Something goes for a long time if it happens for an extended period.
The lizard in the picture has a very long tail.
The opposite of long is short.
Your clothes are loose if they are too big for you. The opposite of loose is tight. The woman in the picture is wearing jeans that are far too loose for her because she has lost weight.