Use a comma between coordinate modifiers. Modifiers are coordinate if they modify the same word. You can test to see if the modifiers are coordinate by inserting and between them. If the description still makes sense, then the modifiers are coordinate.
Ebola viruses are known as filoviruses for their long, filamentlike
appearance under a microscope. [Long and filamentlike
modify the appearance of the virus equally, so a comma is needed between them.]
--"Research Notes," Science News
