2025/08/26 by James R. Thomka, Carlton E. Brett, Donald Bissett +1 · 1 voice
Earth and Planetary Sciences · Environmental Science · #Marine Biology and Ecology Research #Marine Ecology and Invasive Species #Parasite Biology and Host Interactions
paper · doi:10.1080/08912963.2025.2550428
openalex publication_date 2025/08/26 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/21
The Silurian camerate crinoid Eucalyptocrinites Goldfuss commonly served as hosts for pit-forming parasites as well as substrata for encrusters. Although both forms of skeletobiosis may be recorded on the same crinoid calyx, pits and encrusting organisms generally occupy separate portions of the substrate, neither forming a composite association nor showing evidence for interaction. Herein, we describe several Eucalyptocrinites calyxes from the middle Silurian (Wenlock: Sheinwoodian) Massie Formation of southeastern Indiana, U.S.A. that preserve parasitic pits, which were completely or partially overgrown by encrusting bryozoan colonies. The pits, identifiable as Tremichnus paraboloides Brett, indisputably formed while the crinoid host was alive. The overgrowing bryozoans, however, may have encrusted the crinoid either (a) after the death of both the crinoid and the organisms previously occupying the pits or (b) while the crinoid was alive but following expulsion of the pit-forming parasites. Intriguingly, other bryozoan colonies end abruptly at pit boundaries and display thickened rims around pit margins, suggesting that overgrowth was precluded because the pit was occupied by a living parasite. Regardless, this occurrence represents a novel, multi-species skeletobiontic association and highlights the important role that large-calyx crinoids played in fostering biotic interactions in Silurian marine environments.