The lower shell was covered with 56 hemispherical protrusions, seen as a self-destruct system (DW: Dalek), and are possibly also the shield generators.
The voice of a Dalek was electronic, the Dalek creature having no vocal apparatus as such. Their most infamous statement was "EX-TER-MIN-ATE!", with each syllable individually screeched in a frantic electronic scream. Other common utterances included "I (or WE) OBEY!" to any command given by a superior. Daleks also had a radio communicator built into their shells, and emitted an alarm to summon other nearby Daleks if the casing was opened from outside.
The Dalek's eyepiece was its most vulnerable spot, and impairing its vision often led to its main weapon being fired indiscriminately. The Dalek casing also functioned as a fully-sealed environment suit, allowing travel through the vacuumof space or underwater without the need for additional life-support equipment. (DW: The Dalek Invasion of Earth, DW: The Parting of the Ways)
A Dalek was connected to its casing through a positronic link while the mutant itself accesses nutrient feeders and control mechanisms inside its internal chamber. (BFA: The Time of the Daleks)
Due to their gliding motion, some models of Dalek were notoriously unable to tackle st
The power source of the Dalek casing appears to have varied at different points in their history. During his first encounter with them on Skaro, the First Doctor learned that the casing was externally powered by static electricity transmitted through the metal floors of the Dalek City. Isolating a Da
lek from the floor using a non-conductive material shut down the casing, although it was not immediately fatal to the occupant. This weakness was not seen on any other occasion. (DW: The Daleks)
By the beginning of the Last Great Time War the Daleks had adapted their technology to use a form of energy apparently inextricably linked to the process of time travel (possible Artron Energy.) On more than one occasion Daleks and their devices were seen to leech this energy from time-travelers to power themselves. (DW: Dalek, Doomsday).Whatever the power source was that the Daleks used in the interim, it was (apparently uniquely) immune to being drained by the City of the Exxilons.
Strangely, the Daleks retained motive power and the ability to speak even though their weaponry was shut down (strongly suggesting the weapon systems had a separate power supply). The Third Doctorindicated that this was because the Daleks were psychokinetic, the City being unable to absorb psychic energy. Other references to the Daleks having any kind of psychic potential are rather scarce, but on the planet Kyrol the Doctor later discovered an enclave of humanised Daleks who had, through years of meditation, developed their psychokinesis to a remarkable degree. (DW: Death to the Daleks, DWM: Children of the Revolution)
The casing was also booby-trapped making even dead Daleks a dangerous foe. They were frequently equipped with virus transmitters which worked automatically. (NSA: I am a Dalek) Furthermore, the armour contains an automated distress beacon which activates if disturbed. (DW: Planet of the Daleks)The interior mutant was, as Ace described it, a green or pinkish "blob." (DW: Remembrance of the Daleks) It is the brain of the Dalek and the true creature that hates everything that is not a Dalek. The "blobs" are most often genetically-mutated Kaleds or, at times, other species captured by the Daleks and are depicted as having multiple tentacle-like protrusions and a normal sized right eye with the left eye much reduced in size so as to be easily missed. Despite their apparent lack of any motive capability they are shown to be capable of defending themselves, as demonstrated when a Dalek attacked and killed a soldier. (DW: Resurrection of the Daleks)
While typically the Daleks are small mutants, at least one member of the species, Dalek Sec, had extremely large tentacles and was pale green; he could even produce a sac-like membrane that appeared to come from his mouth (most likely a self-induced alteration in preparation for the final experiment). It was this membrane that he used to absorb Mr. Diagoras and transform into a Human-Dalek. (DW: Daleks in Manhattan, Evolution of the Daleks) Before or during the Time War, the Daleks mutated even more, it had a large eye in the centre of its body and tentacles. (DW: Dalek)
During WWII, three Daleks managed to engage a Progenitor and create pure-breed Dalek. Their current appearance is unknown, but presumably less mutated. (DW: Victory of the Daleks)