Body length a tad short of 600mm! Emerged from a sparassid. Found curled up into a Gordian tangle, suggesting a Horsehair Worm or Gordian Worm (due to their knottiness)belonging to the Nematomorpha, usually seen emerging from crickets and grasshoppers. It appears, however, that such worms that come from spiders are more likely mermithid Nematodes. All references I could find quote Poinar 1985. The brief text in ADS2014:(p.19)that deals with nematode parasites of spiders is also copied from that article.
Little seems to be knowm about life cycles or identification of long, tough helminths that live in large spiders. Poinar (1985) mentions mermithids up to 150mm and Nematomorphs that parasitise insects are said to be as long as a meter. By size and general appearance this worm resembles Nematomorphs I've seen emerging from Cockroaches.
I dipped the worm in hot water to kill it so I could satisfy my curiosity about its length. It is now preserved in cane spirits if anyone is interested?
Spider Parasite Digital Research Collection Specimen ID: SPDR-F-0035. Collected by S.A. Keiser. Photographed in laboratory.