Arthropod identification request (a spider with no legs?)
This appears to be the underside of a walnut orbweaver:

These orbweaver spiders are not medically significant.
Spiders often lose their legs in wasp attacks. Some spider wasps will remove the legs and then try to bring the spider to its nest for larvae to feed on. Sometimes they drop their spider victims accidentally.
Some will simply deposit eggs into the spider and leave it there, letting the larvae grow inside the spider and feeding on it from the inside.. these ones don't usually remove the legs - they usually just paralyze the spider.
Spiders can lose their legs through various attacks, but they can also lose their legs in molting accidents... particularly if they are in the middle of a molt and then are aggressively interrupted.