Big evidence of the existence of previously extinct Palaeozoic associations


Big evidence of the existence of previously extinct Palaeozoic associations

In the Palaeozoic era, Crinoids and Corals were two benthic besties, that flourished very well on the seafloor. There have been many examples of such bonds from the seafloor fossil records, where corals were believed to have huge growths of crinoid stems that could climb above the seafloor for filter feeding. The strong bond between the two disappeared some 274 million years ago. They were thought to be extinct until recently, when scientists have found evidence of corals growing from the stalks of crinoids in the floor of the Pacific Ocean, as evident by the work of Hiroki Kise and team published in Palaeogeography, Palaeoclimatology, Palaeoecology.

Crinoids belong to Palaeozoic benthos, the most crinoids are unstalked forms, while the previous was in a relationship with other life forms. Neither Paleozoic corals nor crinoids survived the Permo-Triassic crisis. Now with the appearance of the new groups of crinoids and hexacorals, this ecological niche remained vacant and hence disappeared from marine biotic interactions. In recent times no crinoid-anthozoan relationship has been seen in the seas. The researchers observed 2 new recently discovered analogs of such Palaeozoic association that is Crinoid (Metacrinus rotundus) being the host with hexacorals (zoantharian and actiniarian) being the epibiont to understand the Paleozoic associations. The samples were analyzed under a stereoscopic microscope and pictured using a camera of lens 28-80mm. Microtomography scanning was done for investigating internal structures. While CT scan was done for increasing image resolution. For identification of actininarian DNA barcoding by PCR was done with DNA extraction.

Pakistan Journal of Biological Sciences

They found that crinoid (Metacrinus rotundus) is the commonest species, that forms parabolic feeding fan, as they are passive feeders but diversify to meet the needs. Their stem remained fairly flexible after the attachment of hexacorals. No anatomical change of crinoid stereo has been found at the site of attachment of epizoans. Two epizoans of hexacoral species were found, that is; Abyssoanthus sp. And Metridioidea sp. The Abyssoanthus sp. Though rare, encrusts hard inorganic substrates like mudstones, off the Pacific Coast of Japan. Unlike other colonial zoantharians, this species was composed of uncolonial, single polyps, and was less than 1 cm in diameter, having the broad oral disc, expanded tentacles, and long oral disc. their tentacles were organized in two cycles. Regarding the other species, Metridioidea which is a sea anemone, they conducted a BLAST search and found that the sp. Was related to Galatheanthemum sp. Belongs to the same genus, which is a member of the super family Metridioidea. Its physical features consisted of long columns with cuticular surface and simple flatted ends with the absence of a disc-like structure. Therefore, this sea anemone having the characteristic columnar shape, and the basal disc is known as Metridioidea sp. Indet.

This research provided a big contribution in explaining the gap in the fossil record. This Paleozoic fossil of corals and crinoids hasa calcite skeleton. Because of the inability of corals to be modified by the epibiont, it is believed that this relationship could be present for a long time and simply hasn’t been recorded.


Symbiosis, Actualism, Zoantharia, Actiniaria, Modern analog, Paleoecology, Abyssoanthus sp., Metridioidea sp., Palaeogeography, Palaeoclimatology, epibiont, Paleozoic fossils.