The Zephonim appeared in Soul Reaver; they were the descendants of the vampire lieutenant Zephon. After Raziel returned from the Abyss as a Reaver of Souls, he encountered them in their stronghold: the Silenced Cathedral. The Elder God told Raziel the Zephonim had murdered the Cathedral's human guardians.
Since Raziel's execution, all of the clans had evolved and experienced dramatic physical changes. The Zephonim's evolution had made them spider-like. They were particularly agile, with thin, wiry bodies, and long arms and legs. They walked on all fours most of the time, but they could walk upright if they wanted to. Their fangs were very prominent.
The arachnidan traits of the Zephonim did not stop at their appearance. They could scale most (if not all) vertical surfaces, clinging to them for long periods of time, or dropping down to ambush their prey from above. Curiously, they faced away from the wall while climbing. When they caught humans, they would bind them in thread, to feed from later. The Silenced Cathedral had a room where humans - writhing and wrapped up from head to toe - could be seen swinging from the ceiling and walls. In the Canyons in Blood Omen 2, the Lesser Demons bound humans in a similar fashion.
Adult Zephonim could be distinguished from their fledgling counterparts by the large skin frills that decorated their backs. This clan pupated (evolved) inside the many grey/white cocoons attached to the Cathedral's walls and pipes. Looking carefully, it was possible to see the shape of the enclosed Zephonim's face in the pulsing skin of a cocoon.
There was an amusing glitch involving the Zephonim, most easily replicated in the 'three pipes' room of the Cathedral. On rare occasions, they performed an unusual 'ballerina' jumping movement, leaping straight up and completing a 360° turn in mid-air (or turning 180° one way, then turning back), with their arms outstretched. It appeared to be a loop of their mount wall/drop from wall animations. The glitch seemed to occur when a Zephonim tried to mount a wall that didn't actually exist; they were detecting a suspended ledge instead. With patience, the glitch could be triggered in the 'three pipes' room by having Raziel constantly leap between the ledges there.
In addition, Zephon's resemblance to the Alien Queen (from the movie Aliens ) is often noted. However, there are other signs that the game developers were fans of that film. In particular, amongst the humans ensnared by the Zephonim, there were many dead with gaping holes in their torsos. Their ribs and spinal column were exposed. Sticking strictly within the Legacy of Kain universe, this injury could have been some weird and unlikely homage to Janos Audron, performed by the Zephonim on their victims. Straying outside of Legacy of Kain, it looked like these poor souls had been host to an Alien Chestburster.