A study of diverse cysts developed on fossil echinoderms from Poland results in the recognition that these on Late Jurassic crinoid stems are attributable to the life activity of myzostomidan polychaetes, and those on Middle and Late Jurassic echinoids, to the activity of copepod arthropods. A review of formerly reported cysts of coeval age from Europe and western Asia permits the distinguishing of several types that differ in shape and/or location on the echinoderm skeleton. Although the studied cysts qualify as trace fossils (which require a separate ichnotaxonomy), their ethological and ecological characteristics are presented in terms of interspecific parasite-host relationships. The classical interpretation of VON GRAFF (1885) is affirmed for myzostomidan endocysts in crinoid stems, whereas for echinoid tests a new interpretation is offered for large exocysts ('Halloween pumpkin-mask' type) as having been induced by copepods, comparable in their ethology to those on prcscnt-day biota (hydrocorals) other than echinoderms. A copepod attribution by MERCIER (1936) of cysts (Castexia type) on some Middle Jurassic collyritid echinoids from France is fully accepted. This is supplemented by some new finds in Poland, a re-study of the Castexia cysts from France, and a re-interpretation of former reports from the literature. Eco-ethological consequences of the location of copepods in the ambulacral and peristomial parts of cidaroid and hemicidaroid echinoids are discussed; larval settling apparently took place at the tubefeet pores and gonopores, through which the copepod larvae reached the echinoid's interior and began to parasitize it. Attribution of the discussed cysts to copepods yields, consequently, an extension of the stratigraphical range of the class Copepoda H. MILNE-EDWARDS, 1840, to the Early Jurassic. In POSTSCRIPT, suggested is the bald-sea-urchin disease to have caused some lesions in the collyritid echinoids (Middle Jurassic: Callovian) from France.
