Llwygarua suzannae, Botting & Muir, 2023

Botting, Joseph P. & Muir, Lucy A., 2023, A new thalassematid echiuran worm from the Middle Ordovician Castle Bank Biota of Wales, UK, Acta Palaeontologica Polonica 68 (4), pp. 571-581 : 574-577

publication ID	https://doi.org/ 10.4202/app.01107.2023
persistent identifier	https://treatment.plazi.org/id/8165B75B-FFAF-E97D-7515-5179FE96F9DE
treatment provided by	Felipe
scientific name	Llwygarua suzannae
status	sp. nov.

Treatment

Llwygarua suzannae sp. nov.

Figs. 2B View Fig , 3 View Fig , 4 View Fig .

ZooBank LSID: urn:lsid:zoobank.org:act:ADCFAAFC-D007-496D-AC8A-3809F1CA6F7E

Etymology: After Suzanne Douel, a retired biology teacher who has supported research on the Castle Bank fauna since its discovery.

Type material: Holotype, NMW.2021.3G.99, complete specimen in lateral view . Paratype, NMW.2021.3G.100, complete specimen with folded proboscis from the type locality and horizon .

Type locality: Castle Bank , near Llandrindod, Wales, UK .

Type horizon: Didymograptus murchisoni Biozone, Darriwilian, Middle Ordovician.

Material: Type material and probably also NMW.2021. 3G.101, complete specimen in dorsal view, with fine details lacking, from the type locality and horizon .

Diagnosis. —Trunk widest at anterior, tapering to short, bluntly pointed caudal tip, which curves slightly ventrally; no obvious anal hooks; proboscis approximately half length of trunk and nearly as broad, bilobed with slightly irregular margins and with short anterior projections either side of gutter along the midline; texture of proboscis weakly reticulate. Pair of stout, straight anterior setae. Longitudinal trunk muscles form approximately 8–12 broad bands; oblique transverse musculature finer but also fasciculated.

Description.—Worm with trapezoidal trunk and broad, bilobed proboscis. Holotype ( Fig. 2B View Fig ) preserved in oblique lateral view, and paratype ( Fig. 3 View Fig ) mostly lateral with proboscis folded over and with lobes flattened out to either side. The holotype is 7 mm long and 1.5 mm wide, and the paratype is 5.5 mm long and 1.2 mm wide. The additional specimen is also 5.5 mm long and 1.2 mm wide. The significant information is derived from the holotype and paratype. The specimen NMW.2021.3G.101 ( Fig. 4 View Fig ) shows the same proportions and body shape (including narrowed caudal region), but is complicated by wrinkling and lacks the fine detail to confirm the assignment.

Trunk broadest close to anterior end, tapering gradually towards posterior, then more rapidly in the posteriormost third (change in angle of taper much stronger on ventral side than dorsal). Posterior termination bluntly pointed, bending ventrally ( Fig. 2B View Fig 1 View Fig ). In the paratype, there are several irregular projections ( Fig. 3A View Fig 4 View Fig ) that may result from decay of this region, and possibly reflect some internal structures of the anal region, but are too indistinct to be clearly interpreted.

Surface of trunk is wrinkled, presumably due to compaction of the cuticle, which shows no distinct texture and was apparently smooth. Anterior ventral setal pair visible in holotype (one distinct, the other probably present but partly overlapping compressed margin; Fig. 2B View Fig 4 View Fig ). Setae straight, at least 0.3 mm long (base uncertain), and relatively robust with blunt end.

Multiple dark longitudinal bands are visible in the trunk of the paratype ( Fig. 3A View Fig 1 View Fig , A 2 View Fig ), and less clearly in the holotype ( Fig. 2B View Fig 1 View Fig ); these are interpreted as longitudinal subdermal muscle bands. The number of these cannot be counted accurately due to the superposition of the two sides of the body wall, but the estimated number is 8–12. Finer oblique to transverse lines are superimposed on the primary muscle bands in the paratype, forming narrow bundles (probably of at least 2–3 fibres) at around 70° to the longitudinal structures ( Fig. 3A View Fig 2 View Fig ). Oblique structures only locally visible, but are aligned with steps in trunk outline ( Fig. 3A View Fig 1 View Fig ) and therefore appear to have exerted some control of deformation during burial; holotype shows similarly-angled fabric.

Proboscis ( Figs. 2B View Fig 3 View Fig , B 5 View Fig , 3A 3 View Fig ) with midline separating two lobes, approximately half as long as trunk, and around 80% as wide (depending on angle of flattening). Margin slightly undulating and finely crenulated ( Fig. 3A View Fig 5 View Fig ), but on larger scale effectively straight until broadly rounded apex Fig. 2B View Fig 3 View Fig ). Based on angles of flattening, the two lobes curl inwards ventrally. Internal darker strands mark the midline between lobes ( Figs. 3A 3 View Fig , 4A View Fig 2 View Fig ), around the expected location of the gutter leading to the mouth. Either side of the midline, short (0.1–0.2 mm) sharply rounded projections extend from the apex ( Figs. 2B View Fig 3 View Fig , B 5 View Fig , 3A 3 View Fig ); these projections are also weakly preserved in the additional specimen ( Fig. 4A View Fig 3 View Fig ). The lobes of the proboscis show a distinct polygonal reticulation of darker lines ( Figs. 2B View Fig 5 View Fig , 3A View Fig 5 View Fig ), similar in preservation to that of nervous tissue in arthropods ( Botting et al. 2023b).

Remarks.—The new species is reconstructed in Fig. 5 View Fig . There are no comparable fossil echiurans with which this species could be confused. Coprinoscolex ellogimus Jones and Thompson, 1977 , from the Carboniferous Mazon Creek Biota shows little fine detail but is different in shape (tapered at both ends), with a much smaller, fan-like proboscis and no anterior setae ( Jones and Thompson 1977). Those authors used the lack of setae to argue that the species should be assigned to the extant echiuran family Bonellidae , but this is not strong evidence. The specimens typically also contain Tomaculum -like, cylindrical pellets, for which there is no evidence in the Castle Bank Biota. Such pellets could be produced by various worms, including annelids and priapulids ( Hu et al. 2021), and the assignment of Coprinoscolex ellogimus to the echiurans was based primarily on the proboscis, body form and convoluted gut. Whilst this is reasonably compelling, there is little similarity of Coprinoscolex ellogimus to Llwygarua suzannae gen. et sp. nov.

The most challenging feature to interpret in the new material is the reticulation on the proboscis, which has no obvious counterpart in living echiurans. However, the structures and sculpture of modern echiuran probosces are diverse, including a variety of ridged forms ( Maiorova and Adrianov 2018), and it is possible that this feature represents either a surface texture, or an internal organisation of, e.g., nerves or blood vessels. No such features are known in the very limited material of other echiuran fossils, however, and such anatomical details as could explain the structures are not preserved in Coprinoscolex ellogimus ; at this stage the true interpretation of the reticulation is unknown.

Stratigraphic and geographic range.— Type horizon and locality only.