Those are round worms in his poop - so the wormer is working. Very normal for a 9 week old to be pooping out roundworms after being wormed. Might still see them in a couple more bowel movements, but they should be gone after that. ( I added the warning to the subject line, I've seen plenty of roundworms, but the close-up pics you posted were a bit unexpected).
Gryffon Vom Wildhaus
BH, OB1, TR1, AD
Rottweiler/Hairy Dog mix?? 2004-2015