Dalek (Barusa's universe)

In one of the infinite parallel universes of "possible space", the Daleks were half-insectoid, half-humanoid mutants in casings that had a spider-like appearance, able to fold and unfold. (COMIC: Fire and Brimstone) These Daleks were also carnivorous, able to devour those they killed. (PROSE: The Chronicles of Doctor Who?)

The universe of Barusa
These Daleks were native to a universe where the history of the Doctor was recorded by his grandfather and companion, the Time Lord Cardinal Barusa. (PROSE: The Chronicles of Doctor Who?) In events similar to the creation of the Daleks as witnessed by the Fourth Doctor in his home universe, (TV: Genesis of the Daleks) these Daleks were created by the Kaled scientist Davros on a war-torn Skaro, initially under the pretense of creating life-support systems for Kaled babies born with life-threatening mutations, but actually in an effort to upgrade the Kaleds into the "ultimate killing machines". The Doctor was sent to Skaro by the Master, supposedly to avert their creation, but his attempts to denounce Davros to the Kaled High Council instead resulted in Davros leaking the location of the Kaled base to the Thals, wiping out the Kaleds except for himself and his Dalek creations.

Subsequently, the Doctor was captured by Davros and the Daleks while trying to sneak into the incubator room to destroy Davros's supply of further Dalek embryos. However, before Davros could have his "children" kill the Doctor, the Master intervened, revealing to the Daleks how Davros had betrayed their Kaled ancestros to the Thals. This, rather than a belief in his inferiority, caused the Daleks to turn on Davros and destroy them. Thereafter, they pledged loyalty to the Master, helping him chase the Doctor through time. (PROSE: The Chronicles of Doctor Who?)

Into another universe
At some point, a Dalek ship fell through a spatial rift and emerged in the Doctor's reality in the Magellan Cluster. There, the alternative Daleks came into conflict with the Dalek Hive. The Hive Daleks were terrified by the potential of their parallel counterparts, who took months to subdue even with all of the Dalek Hive's resources. This led the Supreme Dalek to mastermind a preemptive strike on the alternate universe, taking control of the engineered sun known as Crivello's Cauldron in order to turn it into a wormhole that would allow the Daleks to conquer the rest of the Multiverse. By then, only one of the interdimensional Daleks was left alive, being shown by Marquez to the Eighth Doctor.

However, in the few seconds after the portal opened but before the Dalek Hive could cross it, more Spider Daleks came through on the attack (with a group managing to destroy the Supreme Dalek himself), alongside a swarm of Great Vampires from another universe. (COMIC: Fire and Brimstone)

Behind the scenes
These "Spider Daleks" originated as a proposed redesign for the Daleks in a rebooted Doctor Who TV series that would have followed from the Leekley Bible.

The redesign was intended to take full advantage of the then-new technology of CGI, but bore little resemblance to their predecessors. Concept art depicted these creatures as having six-legged, adaptive casings, from which their mutant controller could emerge, wielding claws and lethal weaponry. A brief screen test of these new all-CGI Daleks was broadcast on television as a trailer of sorts, early into the development of what ultimately become the Doctor Who TV movie; it was later released on DVD alongside the TV movie itself.

In the finished Doctor Who TV movie, however, the Spider Dalek was not featured: the Daleks executing in the prologue are heard, but emphatically not seen. Later merchandising and continuity would establish these Daleks to have been "ordinary" Imperial Daleks of the Dalek Prelature.