New aquarium creatures identified

After a lot of research on my part I discovered a critter I needed identified is definitely a spaghetti worm.  How I got it I don’t know.  It could have been inside a shell or attached to some seaweed.  It has made a tube of grainy stuff which I really think is urchin poop.  It “glued” its tube to the inside of a crown conch shell.  It its so fun to watch when it’s using its tentacles which are really long, really skinny almost clear hair-like things.  They remind me sometimes of a large construction crane: gathering material from down below (on the bottom of the tank) and raising it up to the top which would be its mouth.  Too cool.  We have 3 of these critters now.  Check out this link for a cool picture.
On the same crown conch I noticed some black spots but didn’t question it.  Today I saw something amazing rising up from two of the spots.  I’ve discovered that my fish tank has black-spotted feather duster worms.  They are so cool to watch, too.  If disturbed they shrink to nothing but a dot.  Then they cautiously come back like an umbrella opening upward.  Here’s a link for a picture:
We’ve aquired a porcelain crab somehow; probably mixed in with some sea grass and sand.
I am having trouble finding algae for the critters to eat.  We took a trip to Orange Beach on Sunday and were able to scoop from the shore at the Pass some grasses.  The Gulf beach was barren and the Bay beaches have been, too.  We’ve had some storminess today and are expecting more this week so hopefully I’ll be able to gather some loosened grass for the critters to eat.