Arachnoides
Arachnoides is a genus of sea urchin within the family Clypeasteridae, found in the Indo-Pacific oceans. The base is flat and the upper surface is convex.
If you are looking for a fern genus, its name is Arachniodes.Species
The World Register of Marine Species list the following species as being in this genus:-
Arachnoides zelandiae Gray, 1855 New Zealand: Synonym of Fellaster zelandiae