Spider undercarriage

Probably an Orb spider but it's hard to tell from just the stomach :)

I love the 'hook' on the stomach. I've never seen that before (and know little about spiders). I did some looking and didn't come up with a definitive answer (so if anyone knows better...), but the 2 answers I found both involve egg-laying (not a big surprise).

Quoted from the 19th century 'Penny cyclopaedia of the Society for the Diffusion of Useful Knowledge, Volume 1') "...Here there is an organ placed somewhat in the form of a hook...which the spider can move in such a manner a to direct every individual egg...." Penny cyclopaedia of the Society for ... - Google Books

Or from Wikipedia, this could be referring to it (but, not sure) Epigyne - Wikipedia, the free encyclopedia - aparently Orb Weavers "...A still more complicated form of epigyne is found in some of the sheet weavers (Linyphiidae) and orb weavers (Araneidae), where the ovipositor consists of two finger-like projections: first, the more common one, the scape, which arises from the atriolum, and consequently in front of the opening of the oviduct; and second, one which arises behind the opening of the oviduct; this is termed the parmula. Each of these projections may be grooved on the side facing the oviduct, forming a tube." Of course that may be nothing to do with it, but the one big problem with the internet is that you rarely get anything in depth.