Unusual tabulate-crinoid biocoenosis from the Lower Devonian of Morocco

Abstract

The Early Devonian (Pragian: sulcatus to pireneae conodont zones) crinoid-coral biocoenosis from Hamar Laghdad, Morocco contains fragments of crinoid stalks of various taxa encrusted by spherical and ellipsoidal coralla of the tabulate coral Hamarilopora minima. These corals were encrusting host crinoids syn vivo, and this is evidenced by pluricolumnals exceeding 30 elements overgrown from all sides. Most known to date crinoid-epibiont associations display various types of reaction to the epibiont, such as swellings and deformations. In the case discussed here, no clear interaction is visible; therefore, this association can be classified as paroecia. It can be inferred, however, that due to a change in mechanical properties of the crinoid stalk (losing flexibility), the epizoan influence on the host was negative, while the coral was profiting from the elevated position over the seafloor and nutrient-bearing water currents. It can be supposed that this interaction was close to parasitism. No strict species-specific relationship between the epizoan and the host was observed. □ Crinoids, tabulate corals, epizoans, Devonian, Morocco, parasitism, paroecia. The fossil record provides many examples of crinoid columnals encrusted by a variety of epibionts. These in most cases include epizoans, belonging to various groups of sessile invertebrates such as sponges, corals, bivalves, bryozoans, brachiopods, cornulitids, serpulid worms, edrioasteroids and other crinoids as well (e.g.

Differentiating Parasitism and Other Interactions in Fossilized Colonial Organisms

“…Loss of stem flexibility as a result of encrustation would have impacted the host crinoid negatively, suggesting that the association was parasitic. Similar associations have been reported involving a wide range of epibionts, both colonial and unitary, on crinoid stems elsewhere in the fossil record (see references in Berkowski and Zapalski, 2014).…”

“…There is a rich fossil record of sponge borings (ichnogenus Entobia) into corals and other biotic substrates (see Bromley, 2004), which warrant further study in this context. Berkowski and Zapalski (2014) recently described examples of the tabulate coral Hamarilopora minima that encrusted the stems of living crinoids in the Early Devonian of Morocco. Loss of stem flexibility as a result of encrustation would have impacted the host crinoid negatively, suggesting that the association was parasitic.…”

Tabulate Corals after the Frasnian/Famennian Crisis: A Unique Fauna from the Holy Cross Mountains, Poland

“…At least in one specimen we have obtained a longitudinal section through the pluricolumnal (see Fig 3G ). The skeleton adheres to the crinoid skeleton, thus suggesting syn vivo encrustation, as in specimens described from the Lower Devonian of Morocco [ 63 ].…”

Large dwellers of the Silurian Halysites biostrome: rhizosessile life strategies of cystiphyllid rugose corals from the Llandovery of Gotland

“…, ,b), Silurian (Sorauf & Kissling ; Vinn & Mõtus ) and Carboniferous (Pickett ). On the other hand, the presence of sweeper tentacles or similar structures in tabulate corals is equivocal, as preserved polyps show rather uniform tentacles (Copper ); in contrast, tabulates settling on crinoids damaged the host's tissue by either sweeper tentacles or digestive filaments (Berkowski & Zapalski ).…”