How did that bobbit worm get into your tank.

Fistly if you want to understand the marine eco system you have to get a serious grasp on planktonic dipersal of marine life.
Near on 98 percent of all marine life, once born in what ever manner starts out transparent and of a planktonic size.
Even the great blue marlin fish starts out ultra tiny and invisible to the naked eye for its time living in and feeding on the plankton till too large, and with them its too large at approximately 15 mill long and then off it goes now unable to hide with its pelagic life style.


Now inverts, mobile in this case, all start out semi transparent and very small like a half to 3 mililmetres in size.
Once they swim or float their begining of life, then crawl around, they find places to hide, in coral you bought, in rock from an infected tank where they have bred or in sponge, mantis, crabs worms ofr types all satrt out ultra tiny and you get them, but do not see them for ages as they grow.

My last substrate tank my daughter accidently broke a long time ago, so once the kitchen floor became our pool, lol,i transfered all life to the shed tanks,when i tore it town in the sand there was one whopper and 3 tiny ones and never before this put 2 and 2 together as to why i would lose a fish or a shrimp from time ot time over those years.
https://www.google.com.au/search?hl=en&authuser=0&tbm=isch&source=hp&biw=1366&bih=620&ei=YMxtXO2KBJWDoATS4b_wAQ&q=bobbit+worm&oq=bobbit+worm&gs_l=img.1.0.0l10.2551.5026..7992...0.0..0.329.2975.2-10j1......2....1..gws-wiz-img.....0..35i39.mKUeUcfOWKs#imgrc=_&spf=1550699626794