fucoid

adj

1. Resembling or relating to seaweeds of the genus Fucus.

   “The first cell division in zygotes of the fucoid brown alga Pelvetia compressa is asymmetric […]”

2. Of sandstone: bearing seaweed-like markings.

   “Calcareous siltstone, Cambrian Fucoid Beds, earth.ox.ac.uk webpage The Fucoid beds are quite variable in appearance in composition […] The rock unit got its name from the early belief that these markings were the compressed remains of seaweeds (fucoids). Now it is thought that they are the trails left by feeding creatures on the sea floor.”

noun

1. A fucoid seaweed.

   “Among a number of unidentified specimens […] was one of an unusually well-defined, almost perfect frond of a fucoid.”