Of note are 3 Deathworlds, Jurasia, which contains huge lizards, some of the apex predators rivaling humans in intelligence, which appears to have been a research site of some kind before the Age of Strife. That's what the fragments of data that could be extracted from the few computers the locals had managed to protect said, at least.
Aquarius, which is an oceanic Deathworld that the Old Ones apparently tested numerous biophages on, to the point where they were forced to effectively sterilize the planet and start over, for fear of a local virus killing everything were it to reach the greater galaxy. Now the viral and bacterial threats weren't any more dangerous than the commonly-inhabited parts of the rest of the galaxy, though the local fauna and flora were pretty bad, especially in the depths, since the planet had been converted to a more 'conventional' Deathworld later on. With its size sitting at 3.7 times the average inhabited planet, it could, however, provide a great deal of space for aquatic races.
The third world, Hozris, was of great interest to the Mechanicus, as there were mechanical simulacrums of animals, apparently of varieties commonly found on Terra before the AoS. Once they'd made certain that there were no Abominable Intelligences amongst the machines (few exceeded the average cat in intellect, and those were aberrations) they began discussions, both theological and scientific, with the local machine cult, which, despite what one might expect, didn't have roots in a Mechanicus Ark. Instead it was a home-grown cult that worshipped machines, noting that some of the eldest machine animals had been around since shortly after the AoS began, and considering that a sign of technology's superiority to organic evolution.
