You are bidding on a softball sized portion of susswassertang.  It's pretty, it's green and it grows happily in cages or on shelves (I usually anchor it with some green tulle to start with) or anyplace else you want to anchor it.  Very primitive, not a lot of structure, no midrib, stem, root, holdfast. 

"In 2009, a molecular phylogenetic study determined that it is, in fact, a fern gametophyte. It was found to be most closely genetically linked to Lomariopsis lineata, though classification as a distinct species was not ruled out.[8] Efforts to induce süsswassertang specimens to form a sporophyte have failed, which may indicate status as a new species.[9] It is sometimes described as Lomariopsis cf. lineata.[4]"

Fascinating stuff.  For more info, check out the wikipedia link