What is this?
 

In all the years I have been in this hobby... I haven't ever seen one of these.... New to my tank as of the past couple of days. Dosn't seem to move... But i'm not sure. Also looks to have tentacles coming out of it.

https://i.imgur.com/5PjzAYA.jpg?1

https://i.imgur.com/M0n7RcR.jpg?1

I don't know either
One pic shows it as the letter Y.
Did it morph into that from being straight?

No, those are two different ones. Both about 3" away from each other

This is the closest thing I’ve found to it May or may not be it

https://www.melevsreef.com/critter/spaghetti-worm

Yeah I've seen my share of spaghetti worms. Definitely different. I may just remove them and hope for the best lol

maybe a hair worm?

http://reefkeeping.com/issues/2002-06/rs/index.php

A member on another forum suggested Labyrinthulaceae. Which by the very little info I've been able to find online seems accurate. But nothing tells me if it's good or bad!

I spent a some time tonight searching this and as you stated there is very little information about this particular species. What is known is that:

-It is commonly found in sea grasses and have been regularly found on underwater plant leaves

-it is classified as a worm and some also classify it as a fungi

-when found in home aquariums is often misidentified due to its rarity in the home aquarium

-from three separate forum sources (R2R, British aquarists(no longer active) and a German forum) specimens were observed in home aquariums but observers found no negative impact to aquariums but most of these posts were from several years ago I have found nothing since

This is all I could find

Wow! Thank you for doing some leg work! haha. Yeah that's about what I have summed up as well. I think i'm actually going to leave them in there at this time. :twised: