That would be a fairly large spider, but if it lives primarily under water then it's a bit more feasible.
It's probably easiest if it evolved from existing water dwelling spiders.
These spiders bring bubbles of air down for them to breathe. These bubbles may actually act as a shiny lure for fish and larger ocean predators. This means bioluminescence is not required.
If the spider can craft large enough bubbles it may only need its prey to accidentally breach the bubble, the spider could then rapidly seal the breach and the gilled creature would suffocate and become weakened inside the gas atmosphere of the bubble. Allowing the spider to easily finish it off.
Alternatively the spider would simply create a web network which has gaps large enough for it to pass through while a larger creature will get tangled if it tries to follow. Once trapped, the spider can finish off the prey and drag it into its bubble for consumption.
The web, if woven in a mesh, would appear to be slime to the uninitiated. It would have a much higher tensile strength than slime though.
Another sort of out there option is for the spider to actually tend to a small farm of sessile nematocyst-wielding creatures, cnidarians. Weaving a structure for the cnidarians to live on, the cnidarians would sting and paralyse any large creatures who wandered into the web. The spider could then capture the prey and give its corpse back to the cnidarians to feed them and keep things clean. This would be similar to some small crabs who live in sea anemones.