Sangeeta Giri
Zoology
June 2021
An integral part of ecosystems from terrestrial to deep marine environments, annelids are a phylum of segmented bilaterian organisms. The morphological and taxonomic variety of annelids is outstanding, and they have developed a wide range of feeding mechanisms and ecologies. Their interactions and development have been the subject of intense debate over the last century, with significant recent changes made to the body plan of the ancestral annelid, the connection between main groups, and the makeup of the annelid crown group. A strong amount of molecular data suggests that clitellates are descended from polychaetes and that they constitute a paraphyletic grade. Errant, Epibenthicpolychaetes are the oldest stem group annelids found in Cambrian Lagerstedt, demonstrating the primordial nature of annelid features like as biramousparapodia, head appendages, and diversified, simple chaetae. Crown group annelids are thought to be a radiation from the Late Cambrian to the Early Ordovician, with clitellates propagating in the Late Palaeozoic, according to recent data from molecular clocks and the fossil record. The majority of their body fossil record is restricted to deposits with extraordinary preservation, and it is broken up by the acquisition of hard pieces in significant groups. Machaeridians are in reality a clade of crown polychaetes, as shown by the finding of an Ordovician fossil containing soft tissues. They have been around for more than 200 million years and have distinctive calcitic dorsal armour, which makes it possible to analyse their way of life and phylogeny in the context of the annelid body plan. We find the Cuniculepadida, a distinct clade of machaeridians, which has many adaptations for burrowing.
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