Spider Dalek

The Spider Daleks were slightly larger than the standard Dalek, but with eight legs. They were more maneuverable than standard Daleks, but more vulnerable at their joints. The Thals believed that this design had been abandoned for centuries. Giant-sized versions, known as Striders, were ten times larger than the standard Spider Dalek. (EDA: War of the Daleks)

Other information
A faction of Daleks from a parallel universe resembled Spider Daleks, and were viewed as abominations by the Daleks of the "main" universe. (DWM: ''Fire and Brimstone)

Behind the Scenes
The Spider Dalek was a new version of Dalek which might have appeared in a proposed revival of Doctor Who developed during the mid-1990s. (A backdoor pilot for the proposed revival appeared as Doctor Who: The TV Movie.) A short CGI test of the new version of Dalek leaked to the internet.