Mieridduryn bonniae, Pates & Botting & Muir & Wolfe, 2022

Pates, Stephen, Botting, Joseph P., Muir, Lucy A. & Wolfe, Joanna M., 2022, Ordovician opabiniid-like animals and the role of the proboscis in euarthropod head evolution, Nature Communications 13 (1), pp. 1-15 : 2

publication ID	https://doi.org/ 10.1038/s41467-022-34204-w
DOI	https://doi.org/10.5281/zenodo.7346852
persistent identifier	https://treatment.plazi.org/id/03FD8143-EC07-FFAC-FCBC-FF07FCEC9CF0
treatment provided by	Tatiana
scientific name	Mieridduryn bonniae
status	nov. gen. et sp.

Treatment

Mieridduryn bonniae nov. gen. et sp.

Figures 1 – 5 View Fig View Fig View Fig View Fig View Fig , Supplementary Figs. 2 – 4 View Fig View Fig View Fig

Etymology. After Bonnie Douel, niece of the site owners and fossil devotee; the family has followed and supported the research extensively since the discovery of the fauna.

Holotype. NMW.2021.3 G.7 known from part and counterpart. Counterpart preserves anterior portion only.

Locality and horizon. Collected from the Darriwilian (Middle Ordovician, Didymograptusmurchisoni Biozone ) Gilwern Volcanic Formation at Castle Bank , near Llandrindod, Powys ( UK) 33, 34.

Diagnosis. As for genus, by monotypy.

Description. NMW.2021.3 G.7 preserves the head region and anterior portion of the trunk ( Fig. 1 View Fig ). The specimen, which measures ~13 mm along the dorsal margin (not including proboscis), is twisted so that the anterior provides an oblique-lateral view, which becomes more oblique-ventral towards the posterior.

The head region preserves evidence for a dorsal sclerite, annulated proboscis, and posterior-facing mouth composed of sclerotized plates.The dorsal sclerite (length ~2 mm) has a rounded lateral margin. The proboscis, which is a single structure and not an overlapping pair of appendages, measures ca. 3 mm along its dorsal margin, is annulated, curves ventrally, and displays slender spines at regular intervals (~0.2 mm spacing, one per two to four annulations) along its dorsal margin ( Figs. 2a View Fig , 3 View Fig , 4d View Fig , Supplementary Fig. 2 View Fig ). Evidence for a posteriorfacing mouth is provided by the gut trace, which twists ventrally where it connects to the mouth ( Figs. 2a View Fig , 4c View Fig , Supplementary Fig. 3 View Fig ). The mouth is ~0.4 mm in diameter and preserves evidence for small, lightly sclerotized plates subequal in size (Supplementary Fig. 4 View Fig ). Plate boundaries are most visible at the anterior and posterior of the ring; the left and right sides display greater disarticulation and are less complete (Supplementary Fig. 4 View Fig ).

The trunk bears two sets of appendages: dorsolateral flaps and ventral lobopodous limbs. Flaps intersect with faint curved boundaries, interpreted as the body margin, and display a subrectangular outline with rounded margins ( Fig. 5b View Fig ). Flaps decrease in size towards the posterior (lf1 measures ~3 mm along its long axis, lf3 ~2 mm). Although most flaps display a smooth external surface, the anteriormost flaps provide evidence for internal linear features, interpreted as strengthening rays ( Figs.2b, c View Fig , 4c View Fig ). These are visible in the left anterior flap, which has been split obliquely, revealing interior structures. The strengthening rays run parallel to the long axis of the flap and cover most of the flap width. Both anterior flaps display a darker region that covers most of the surface facing the body midline. This darker region preserves fine lines that run perpendicular to the strengthening rays, interpreted as setal structures. Additional setal structures protrude from underneath the posterior margins of other flaps (e.g. Fig. 5b View Fig ). Towards the posterior, the body is twisted and the swimming flaps become preserved more obliquely. This reveals a second ventral series of lobopodous limbs ( Fig. 5c, d View Fig ). These limbs are triangular in outline and display lineations that run perpendicular to the long axis, interpreted as annuli. Spines protrude from the posterior margin ( Fig. 5c, d View Fig ).

Remarks. The unique combination of characters, including some previously considered exclusive to opabiniids (annulated proboscis) and radiodonts (dorsal spines on the protocerebral appendage) supports the erection of a new genus and species. Phylogenetic analyses support Mieridduryn bonniae nov. gen. et sp. as the most stemwardmember of the euarthropodstem lineage thatbears dorsal spines on the protocerebral appendage and dorsolateral flaps with strengthening rays, and most crownward member to exhibit lobopodous ventral limbs (further remarks in Supplementary Information).