PREFERENCES OF CORNULITES FOR ANTHRACOSPIRIFER VERSUS PUNCTOSPIRIFER IN THE CHESTERIAN BANGOR LIMESTONE, ALABAMA, USA

Punctae in brachiopods have been argued to deter shell-fouling organisms. The enigmatic sclerobiont, Cornulites, is a common encruster of Paleozoic brachiopods, frequently found attached to spiriferides and often considered to live in near symbiosis or even parasitism with its brachiopod host. In the Bangor Limestone (Chesterian) of Alabama, two spiriferide brachiopods – Anthracospirifer and Punctospirifer – co-occur and are of similar size and morphology, but the former is impunctate whereas the latter bears punctae. These two taxa, in the presence of the common encruster Cornulites, created a “natural experiment” for the effects of punctae on encrustation.

Cornulites clearly prefers Anthracospirifer rather than the punctate Punctospirifer, encrusting Anthracospirifer more frequently than the other spiriferide. On both brachiopod taxa, Cornulites significantly attached close to, or on, the fold and sulcus, most often parallel to plicae. Therefore, although Cornulites preferred the impunctate brachiopod, the larvae preferentially settled near the area of the exhalant currents, regardless of whether the host was punctate or not.

These results support the hypotheses that Paleozoic sclerobionts, and particularly in this study, Cornulites, preferred impunctate brachiopods, and that some sclerobionts taxa lived at least commensally with their hosts, benefiting from exhalant currents generated by their live brachiopod substrates.