Hydroides elegans

Hydroides elegans is a species of tube-forming serpulid worms. It is a harbour fouling invasive species, in contrast with "Hydroides norvegica" with which it is sometimes confused.
"Hyastenus hilgendorfi" is a species of "decorator crab" which uses other organisms to cover its body and in a study in the Suez Canal "H. elegans" was one of the most frequent epibionts.
Hydroides elegans is well known to settle on man-made objects, and build large aggregations of calcerous tubes, and perform "calcification, which often leads to difficulties in extracting fossil fuels". Since they are an invasive species, they must require the contact of a bacterial biofilm to begin settlement.