After looking back at some of my notes and the squid I attempted, I am pretty sure these are octopus eggs. Most squid lay their eggs in capsules containing multiple eggs where octos always string individual eggs to a substrate (or it appears to each other in this case). Egg size makes me think these will be a small egg species and will hatch out about the size of a grain of rice. Sadly we have not discovered a way to keep them alive in captivity, proper food seemly the major problem.
This paper includes a very good video of what to expect at hatching. The animals in the video are large egg species and have been successfully raised to adults in an aquarium but the hatching will be similar. The white round ball between the arms is the remains of their yolk sack. This should be mostly consumed before a successful hatching but does provide the first couple of day of food.
Squid, octopus, and cuttlefish—even to scientists who study them—are wonderfully weird creatures. Known as the soft-bodied or coleoid cephalopods, they have the largest nervous system of any invertebrate, complex behaviors such as instantaneous camouflage, arms studded with dexterous suckers...
The video shows Octopus bimaculoides (colder water animal, typically from the US West Coast) eggs hatching. This is a large egg species where I suspect yours are small egg. The small egg hatchlings are typically not fully formed and float in the currents for about a month where the large egg animals typically find their way to the substrate after about 1 week where they find food among the rocks. I have no good guess as to what kind of octopus these may be. Unfortunately, a photo at hatching won't help but it would be nice to have a picture or two in the thread as they develop and hatch.
These little guys may be premature in that they still have a very large yolk sack attached. It will feed them until it is gone but it is typically a bad sign when they hatch with it being this large. If you can get your hands on any new hatch larvae, it is worth trying to add it to the tank for food. We have seen some minor success with new hatched crabs but little else has worked. Any tiny moving thing is worth a try except brine shrimp as we know they do not provide enough important fats.