A new bubblegum coral from the Nazca Ridge reveals chitin as the structural scaffold of skeleton-less Paragorgia colonies

Abstract Bubblegum corals ( Paragorgia ; Corallidae) form among the largest branching colonies in deep-sea environments despite lacking an axial skeleton. How these octocorals maintain structural cohesion using only sub-millimeter sclerites has remained unexplained. Here we describe Paragorgia quitinosa Sánchez & Easton n. sp., collected at 670 m depth on the Nazca Ridge (southeastern Pacific) during the Schmidt Ocean Institute RV Falkor (too) expedition FKt240708, and report the first evidence of visible chitin in octocoral tissues. The new species is diagnosed by autozoids and siphonozoids retracted on prominent, rounded mounds, large 8-derived radiate capstan sclerites (mean 0.095 mm), and canal walls composed of a polysaccharide substance resistant to dilute hypochlorite digestion. Scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), FTIR, RAMAN and TMS/GC-MS analyses confirm the presence of chitin in the perforating and boundary canals of the coenenchyme in this species and a second Paragorgia sp. Micro-XCT imaging reveals that the holotype is a reproductively active female bearing multiple oocyte cohorts exclusively in siphonozoids. Phylogenetic analyses based on ultraconserved elements (UCEs) and concatenated mitochondrial protein-coding genes place P. quitinosa within Paragorgia , sister to P. johnsoni and P. jamesi , and confirm that Sibogagorgia is polyphyletic. These findings establish that chitin forms a structural canal network throughout the coenenchyme of skeleton-less bubblegum corals—the third report of chitin in Anthozoa after sea anemones and black corals—and suggest a biomechanical role of chitin in the octocoral coenenchyme, potentially explaining the remarkable size and flexibility of skeleton-less branching octocoral colonies.