Phosphannulus on crinoid stems

Small phosphatic tubes assignable to the genus Phosphannulus Müller, Nogami & Lenz, 1974 (Order Hyolithelminthes) occur in swellings on Mississippian to Permian age crinoid stems. The swellings resulted from epizoic Phosphannulus specimens being engulfed by growing crinoid stems. At least some Phosphannulus specimens were probably ectoparasites of the crinoids. Similar fossils of Ordovician age that were previously presumed to be a myzostomid polychaete worm are also shown to be Phosphannulus. A true fossil myzostome gall is illustrated for comparison with the Phosphannulus specimens.