That’s before blood coagulants evolved, from a quick Google search… so… maybe it was not particularly needed and they still did suck on blood just… slower.

Is that more or less disturbing?

Instantly made me think of the pit scene from the 2005 movie King Kong … especially the part with the giant worms

they still do, extant species will swallow prey hole, its the predatory leech, snails, frogs, or anything. i suspect this was also the basis for the goauld symbiotes from sg1. in sg1 they had the more ancient predatory(hemiparasites) forms that dont need hosts, and the current ones thare obligate parasites.