There were several dead insects lying in the garden.
I found a deer carcass on the mountain path.
The police are identifying the remains.
A small animal's carcass was found near the river.
The workers disposed of the dead fish.
遺体 is a respectful, formal term used for a deceased person's body (e.g. at a funeral), whereas 死骸 lacks that respectful tone and is common for animals.
亡骸 is a literary, gentle word for a deceased person's remains, while 死骸 is more neutral and commonly applied to animals or insects.
死骸 usually refers to the carcass of an animal (or a corpse viewed coldly as a mere object), while 屍 is reserved for human corpses in solemn or literary contexts.
Standard kanji spelling; commonly used in news and general writing.
Search-only mixed kanji-kana form; not a standard spelling.
Rarely used kanji form; 屍 is a non-jōyō character that specifically means corpse.
Compound of 死 (し, 'death') and 骸 (がい, 'remains, skeleton'). The reading がい for 骸 is the on'yomi.