What animal / insect carcass is this? (Victoria, Australia)
This is a tadpole shrimp. The most common species here down under is Triops australiensis.

Here is an image of it:



Source: https://www.flickr.com/photos/euprepiosaur/23782620153

Here is some info from Western Australia Museum (I found nothing on Victoria Museum): http://museum.wa.gov.au/creature-feature-tadpole-shrimp

PS: This is not a duplicate of this question because the species here is clearly different.