green flat wormy things?

[norgebyblood]

ok so near the end of my octos life these really weird green THINGS started showing up in the sand and rocks. they were thin, flat, and dark green like a green brittle star color and when u pinched them, they would divide and keep living. we gave the tank back to my teacher with the sand and such still in it (against my advice, parents werent concerned). also, my mom said that on his last full day, the worm things appeared to be attacking the octopus, as was the brittlestar (my guess with the star is that it thought the octo was dead, managed to mangle an arm before mom wrestled the two apart) anyone know what the heck these things are?????

 

[OB]

Sounds like a variety of Platyhelminth to me...