I am doing research on algae from the Upper Cretaceous of Colombia, South America.  The algae I am working with is approximately 5 to 30 µm in size.  The individuals have a well defined "head" or "cap", a well developed "thallus" or "stipe" (I can't tell the difference) and a noticeable "holdfast".  Because these are fossil forms, about all I have to work with is the external morphology (size and shape).  Some forms have the same general shape as, Udotea, some have a "flower-looking" cap as Acetabularia, and some are more globose in shape with a short stalk and holdfast as in the genus Ulva.  I can not find anywhere in the literature where they have been reported and, in the field of paleontology, I have nobody that seems to be interested in talking with me.  I am will to share my photographs online with anyone.  It would be a real help to know what the environment of deposition was.  I am assuming that it was probably shallow, clear and quite water (because of their size) but I am not sure.  Any help would be appreciated.