Microscopic black dots on an acropora frag base. Worms? Snails?

[A.Jones]

I recently got two acropora frags with loads of densely packed tiny black dots around the base of the coral. With 25x jeweler's glasses they look like maybe flat worms but under a microscope they look like tube worms or tribe snails. But under the microscope they also look like they are in an egg sac. Anyone seen this before?

 

[A.Jones]

I recently got two acropora frags with loads of densely packed tiny black dots around the base of the coral. With 25x jeweler's glasses they look like maybe flat worms but under a microscope they look like tube worms or tribe snails. But under the microscope they also look like they are in an egg sac. Anyone seen this before?