It's not unusual to find a single marbled cellar spider carrying her egg sac, but this was the first time I've ever observed two adults with a single egg sac. They were on my front porch, so it was easy for me to check on them periodically for a couple of days until the spiderlings hatched. The adult on the right is still with the spiderlings, but the other one is very close by. I didn't observe any aggressive behavior, so it would appear that both adults were guarding the egg sac. Could the adults be "mommy" and "daddy" longlegs? These spiders don't appear to be as sexually dimorphic as some other species, but the individual on the left does have slightly larger and darker palps. Is that one male? If any spider experts out there are willing to shed some light on this behavior, I would greatly appreciate it. Species ID is based on the dark ventral abdominal stripes, overall pattern, and long legs.