New soft-bodied panarthropods from diverse Spence Shale (Cambrian; Miaolingian; Wuliuan) depositional environments

Abstract The Cambrian (Miaolingian; Wuliuan) Spence Shale Lagerstätte of northern Utah and southern Idaho is one of the most diverse Burgess Shale-type deposits of Laurentia. It yields a diverse fauna consisting of abundant biomineralized and locally abundant soft-bodied fossils, along a range of environments from shallow-water carbonates to deep-shelf dark shales. Panarthropods are the dominant component throughout the deposit, both in time and space, but whereas the trilobites and agnostoids are abundant, most of the soft-bodied taxa are only known from very few specimens. Additionally, the knowledge of soft-bodied panarthropods is currently largely limited to locations in the Wellsville Mountains of northeastern Utah. This contribution describes 21 new soft-bodied panarthropods from six locations, including the first occurrences of soft-bodied panarthropods in the High-Creek, Smithfield Creek, Spence Gulch, and Two-Mile Canyon localities. Additionally, we report the presence of bradoriids— i.e., Branchiocaris pretiosa Resser, 1929, Perspicaris? dilatus Robison and Richards, 1981, Naraoia? sp. indet., Thelxiope cf. T. palaeothalassia Simonetta and Delle Cave, 1975, and Tuzoia guntheri Robison and Richards, 1981—for the first time from the Spence Shale Lagerstätte; the first reported occurrence outside of the Burgess Shale for Thelxiope cf. T. palaeothalassia; and the first Wuliuan occurrence of Tuzoia guntheri. We also report on a new hurdiid carapace element and additional specimens of Buccaspinea cooperi? Pates et al., 2021, Dioxycaris argenta Walcott, 1886, Hurdia sp. indet., and Tuzoia retifera Walcott, 1912. This new material improves our understanding of the panarthropod fauna of the Spence Shale Lagerstätte and substantially increases our understanding of the distribution of the described taxa in time and space.

The Cambrian (Miaolingian, Wuliuan) Spence Shale of northeastern Utah and southeastern Idaho occupies a distinctive position among the Lagerstätten of the Great Basin, because it preserves a range of environments from shallow-water carbonates to deep-shelf shales.Although this by itself is not unique, the fact that biomineralized and soft-bodied organisms are found in all of these environments, and the biota differs between localities (Kimmig et al., 2019b;Whitaker et al., 2022) makes the Spence Shale a deposit of utmost importance to understanding Cambrian communities and biodiversity.Whereas the depositional environment varies within the Spence Shale, all known exposures are dominated by panarthropods (Kimmig et al., 2019b;Whitaker and Kimmig, 2020).This is not surprising, because panarthropods usually dominate Cambrian Lagerstätten (Robison et al., 2015;Paterson et al., 2016;Hou et al., 2017;Nanglu et al., 2020;Yang et al., 2021).
Here we describe 21 new specimens of exceptionally preserved panarthropods from six localities of the Spence Shale, including a new hurdiid carapace element; the first specimens of Naraoia?Walcott, 1912, Thelxiope cf.T. palaeothalassia Simonetta and Delle Cave, 1975, Perspicaris? dilatus Robison and Richards, 1981, Branchiocaris pretiosa Resser, 1929, and Tuzoia guntheri Robison and Richards, 1981; the first bradoriids; as well as new specimens of Dioxycaris argenta Walcott, 1886 from the deposit.In addition, Naraoia?sp.indet.represents the first occurrence of a soft-bodied taxon from the Two-Mile Canyon locality; Dioxycaris argenta and the bradoriids are the first soft-bodied panarthropods from the Spence Shale type-locality of Spence Gulch; Branchiocaris pretiosa is the first soft-bodied panarthropod from the Smithfield Creek locality; and the bradoriid from High Creek represents the first softbodied panarthropod from this location.These specimens not only extend the geographic and stratigraphic range of these taxa, but also add to the already diverse panarthropod fauna of the Spence Shale, suggesting that there might be more species to be found in currently understudied Spence Shale localities.

Geological setting
There are several Lagerstätte intervals that preserve soft tissues within the Spence Shale Member of the Langston Formation.The deposit is regionally extensive, with outcrops in southeastern Idaho and northeastern Utah (Fig. 1).The Spence Shale Member ranges in age from Mexicella mexicana to Glossopleura walcotti biozones (Cambrian, Miaolingian, Wuliuan, 507.5-506Myr) (Liddell et al., 1997;Kimmig et al., 2019b), with all soft-bodied fossils to date coming from the Glossopleura walcotti Biozone.It was deposited on a slope on the passive western margin of Laurentia, and outcrops record an overall increase in depth from Utah to Idaho.The Spence Shale Member ranges from ∼9 m at Blacksmith Fork to ∼120 m at Oneida Narrows, conformably overlies the Naomi Peak Limestone Member of the Langston Formation and, is in turn, conformably overlain by the High Creek Limestone member of the Langston Formation.Figures 2, 3   Description of new material.-KUMIP579779 (Fig. 2.1, 2.2) is an isolated frontal appendage that measures ∼13 mm along the dorsal margin.Eight well-defined podomeres with tall rectangular outlines (Fig. 2.2, pd2-pd9) are preserved.The appendage is bent, with the five podomeres of the distal region orientated near-parallel to the endites borne by the podomeres of the intermediate region.Evidence for an additional ninth podomere is provided by the endites.Four endites, approximately three times as long as the height of the podomere to which they attach, are preserved (Fig. 2.2, en1-en4).The distal three clearly attach to a podomere, but the podomere that should bear en1 is missing.Endites are curved, with their tips approximately perpendicular to the bases, and bear robust triangular auxiliary spines 2-3 mm in length (Fig. 2.2, aux).A short (submillimeter), straight terminal spine is present (Fig. 2.2, ts).
KUMIP 495356 (Fig. 2.3,2.4) is a more poorly preserved partial frontal appendage.At least four, possibly five, endites are present (Fig. 2.4, en1-en5?) proximal to poorly preserved organic material that might represent distal podomeres orientated ventrally as in KUMIP 579779 (Fig. 2.4, pd?).Endites are incomplete at their tips, but display a prominent curve, and bear robust triangular auxiliary spines ∼1 mm in length (Fig. 2.4, aux).Journal of Paleontology:1-24 KUMIP 491056 (Fig. 3.1, 3.2) is an isolated frontal appendage preserved laterally compressed that comprises at least 10, likely 11, podomeres and measures ∼11 mm along the dorsal margin.Podomeres have tall rectangular outlines and decrease in size distally.Six plate-like endites, borne by intermediate-region podomeres (pd3-pd8), can be observed.The proximal three endites (Fig. 3.2, en3-en5) measure ∼6 mm along the long axis, approximately twice the length of the height of the podomere to which they attach.These endites display a slight curve, orientated convex forward.The distal three endites in the intermediate region (Fig. 3.2, en6-en8) are incomplete, but run parallel to the proximal part of en3-en6.Two reduced endites are observed on the distal podomeres (Fig. 3.2, de).No dorsal spines or terminal spines were observed.
KUMIP 495355 (Fig. 3.3-3.5) is an incomplete isolated frontal appendage preserved laterally compressed (Fig. 3.3, app1), in close association (∼10 mm) with additional organic material, potentially a second poorly-preserved partial appendage in oblique ventral view (Fig. 3.3,app2).The well-preserved appendage (Fig. 3.3, app1) measures ∼9 mm along the dorsal margin, and comprises at least six, possibly up to eight, tall rectangular podomeres (Fig. 3.5, pd).Five endites approximately three times as long as the height of the podomere to which they attach are preserved (Fig. 3.5, en2-en6).The proximal four endites (Fig. 3.5, en2-en5) measure ∼8 mm along the long axis, the distalmost endite (Fig. 3.5, en6) measures ∼6 mm.A possible broken endite is associated with pd1 (Fig. 3.5, en1?).Complete endites are straight and bear small (submillimeter) auxiliary spines, with a larger ∼1 mm auxiliary spine orientated distally at their tips.The dorsal surface and distal part of the appendages are incomplete, precluding the observation of dorsal or terminal spines.The associated organic material tentatively interpreted as a partial poorly preserved appendage (Fig. 3.3, app2) measures ∼7mm along its dorsal margin.A number of linear divisions observed are interpreted as podomere boundaries.A ventral protrusion extends from the most proximal of these, interpreted as an incomplete endite (Fig. 3.3, en), but at least five further divisions can be observed (Fig. 3.3,arrows).The proximal and distal portions of this appendage are not preserved, and it is associated with additional unidentified organic remains.
Remarks.-These appendages can be confidently assigned to the family Hurdiidae within Radiodonta, because they are composed of podomeres bearing unpaired plate-like endites with endites along a single margin only.Although both appendages are incomplete, the separation of the distal articulated region of the appendage into two distinct regionsthe intermediate one with plate-like endites and distal one with either reduced or no endites-provides further support for this assignment.Within Hurdiidae, these appendages bear most similarities to genera Buccaspinea and Hurdia.Distinguishing between these genera based only on frontal appendages is not straightforward.Both genera possess elongate endites that can bear robust and elongate auxiliary spines.Endites in Buccaspinea are far longer than the height of the podomere to which they attach (up to six times; Pates et al., 2021a;Fig. 4), and auxiliary spines are very robust in this genus.Endite length to podomere height ratios in Hurdia are generally between 1:1 and 2:1 (Fig. 4), and auxiliary spines can be elongate and hooked (e.g., Moysiuk and Caron, 2019), but are generally less robust than in Buccaspinea.Reduced endites in the distal region have been observed in both Buccaspinea and Hurdia (e.g., Pates et al., 2019Pates et al., , 2021a) ) but are not known in all Hurdia appendages (e.g., Daley et al., 2013).The extent of curvature and relative width of endites observed in hurdiid fossilized appendages can depend on orientation of preservation relative to bedding (Pates et al., 2018a) and/or relative mesial and distal curvature (Moysiuk and Caron, 2019).
Considering all of these details together, KUMIP 579779 and 495356 are considered more likely to be Buccaspinea and KUMIP 491056 and 495355 more likely Hurdia, although these assignments are only tentative, as outlined below.
Evidence in support of identifying the two appendages as possible Buccaspinea (Fig. 2) comes from the relative length of their endites to podomeres, and the robust nature of the auxiliary spines.The relative length of endites to podomeres in KUMIP 579779 (∼3:1) exceeds those of figured Hurdia specimens from the Burgess Shale and Spence Shale (Fig. 4) and is comparable to that of KUMIP 314040 (Pates et al., 2018, fig. 2.3) that was recently tentatively reassigned to Buccaspinea (Pates et al., 2021a).The lack of clear podomeres in KUMIP 495356 precludes measurement of this ratio for this specimen.Both specimens display robust auxiliary spines that overlap the endite immediately distal to the one to which they are attached, just as in the holotype (Pates et al., 2021a) and other Spence Shale specimens tentatively reassigned to the genus: ROM 59634 (Daley et al., 2013, fig.24C), KUMIP 314040 (Pates et al., 2018a, fig. 2.3, 2.4), andUU 18056.34 (Lerosey-Aubril et al., 2020a).Hurdia appendages typically display less-elongate auxiliary spines that only partly overlap the endite anterior to the one to which they are attached (e.g., Daley et al., 2013, fig. 12, fig. 24A, B, D), although this could in part be due to the distal tips of endites not being completely prepared out the matrix (compare Moysiuk and Caron, 2019, fig.3e to Daley et al., 2013, fig. 12 C).Hurdia auxiliary spines also tend to be less robust than those of Buccaspinea.However, these two appendages (KUMIP 579779 and 495356; Fig. 2) cannot be confidently assigned to Buccaspinea because they could be considered Hurdia appendages with particularly elongate endites and robust auxiliary spines, because these features do vary within the genus.Furthermore, the lack of reduced endites in the distal region (four are observed in the type specimen of Buccaspinea; Pates et al., 2021a) also precludes confident assignment to the genus.Reduced distal endites are known from a single Spence Shale Hurdia specimen, ROM 59651 (Daley et al., 2013, fig. 24D), and numerous Burgess Shale specimens (e.g., Daley et al., 2013, fig. 12), although other published examples lack evidence for distal endites.
Evidence in support of identifying KUMIP 491056 and specimens (Fig. 4), comparable to what was measured for KUMIP 579779 (Fig. 2).Those of KUMIP 491056 are incomplete, precluding measurement of a ratio, however what is preserved is < 2:1, the usual range for Hurdia appendages.Both specimens lack prominent auxiliary spines, although this could be due to these spines being overlain by the endites, due to the orientation of preservation.These two specimens appear to display different extents of curvature.The convex forward curvature of endites observed for KUMIP 491056 is also known from KUMIP 314145, a previously described Hurdia appendage from the Spence Shale (Pates et al., 2018a, fig. 2.1).KUMIP 495355 endites can be determined to be mostly straight and lack a prominent mesial or distal curvature, because the spines at the tips of the endites farthest from the ventral margin of the podomeres can be observed (on endites 5, 6, and possibly 4), and the visible podomere boundaries provides evidence of lateral (rather than frontal) compression.If endites had a prominent mesial curve, then the tips of the endites would not be visible (as they are not in KUMIP 491056).In addition, breaks or deformities from compression would be visible, or the curvature would be visible in the specimen.The straight endites of KUMIP 495355 (Fig. 3.3,app1) are best compared to KUMIP 314042 and 312405 (Pates et al., 2018a, figs. 2.5, 3).
In addition to relatively straight endites, both of these previously described specimens display a distalmost plate-like endite that is shorter than the others-a feature also observed in KUMIP 495355 (Fig. 3.3,app1) and other Spence Shale Hurdia appendages (Daley et al., 2013, fig. 24A, B, D;Pates et al., 2018a, fig. 2.1, 2.2).The oral cone adjacent to the pair of appendages in KUMIP 312405 bears internal tooth rows, confirming the identity of these appendages as Hurdia (Daley and Bergström, 2012;Pates et al., 2018a, fig. 3).Thus, despite the relatively elongate nature of the endites in this specimen, assignment to Hurdia is preferred, albeit only very tentatively.
The affinities of the possible second appendage on slab KUMIP 495355 (Fig. 3.3, app2) are less clear.If the single endite in this possible appendage is interpreted as the distalmost of the plate-like endites of a hurdiid appendage, a total of six podomeres lacking endites would be present distal to the series of podomeres bearing plate-like endites.Notably, KUMIP 314178 (Pates et al., 2018a, fig.2.2) also displays a similar array of five very tall rectangular podomeres distal to the podomeres bearing plate-like endites, which are similar to those of KUMIP 495355 (Fig. 3.3, app1), as noted above.Thus KUMIP 495355 (Fig. 3.3, app2) is tentatively identified as the pair of KUMIP 495355 (Fig. 3.3, app1).Family indet.Gen. et sp.indet.
Description.-KUMIP490912 (Fig. 5) is a partial isolated appendage that measures ∼40 mm along the dorsal margin.Evidence of at least 11 podomeres can be tentatively identified.Only a small amount of material remains of pd1, which is separated from pd2 by a curved boundary (Fig. 5, pd1, pd2).Podomeres display a tall rectangular outline in both intermediate and distal regions of the appendage (proximal region most likely not preserved).The middle part of the appendage is not preserved, and the distal region is curved ventrally, approximately perpendicular to the intermediate region.The ventral margin is not well preserved, and only the base of a single endite can be tentatively identified (Fig. 5, en6?).The dorsal margin is well preserved proximally but not distally.No dorsal spines are present on pd2-pd4, and the dorsal margin is not preserved between pd5-pd8.Small protrusions from the dorsal surface can be seen on pd9 and pd10, which might be dorsal spines (Fig. 5, ds?), however these features cannot be confidently distinguished from the incomplete dorsal margin and indents resulting from boundaries between podomeres.
Material.-KUMIP490912, a partial frontal appendage preserved as a lateral compression.
Remarks.-This specimen can be identified as a partial arthropodized appendage, because it is sclerotized and composed of articulating segments (Ma et al., 2014).The curvature, podomere shape, and podomere number are all compatible with a radiodont affinity.Because the appendage is incomplete, and only the base of endites in the proximal region are preserved, assignment to the family level is difficult, with possible arguments favoring an amplectobeluid or hurdiid affinity.The comparatively low number of podomeres (11, assuming that there are no additional proximal podomeres missing) and the distal region approximately perpendicular to the proximal region are both characters observed in hurdiid radiodonts.This includes both Buccaspinea and Hurdia, the hurdiid radiodonts known from other material from Miners Hollow in the Spence Shale (described above), although the amplectobeluid Lyrarapax (only currently known from the Stage 3 Chengjiang in China) also bears only 11 podomeres in its distal articulated region (Cong et al., 2014(Cong et al., , 2016;;Liu et al., 2018).The putative dorsal spines lack the size and recurved nature common for distal podomeres of amplectobeluid and anomalocaridid radiodonts (e.g., Amplectobelua stephenensis Daley and Budd, 2010, Anomalocaris canadensis Whiteaves, 1892; see Daley and Budd, 2010;Daley and Edgecombe, 2014), however this could be accounted for by their poor preservation.The strong curvature or the appendage distally is also observed in both amplectobeluid and hurdiid appendages.Features that would allow more confidence in assigning the isolated appendage specimen to Hurdiidae (e.g., plate-like spines, presence of auxiliary spines on one margin of endites only) or Amplectobeluidae (e.g., hypertrophied proximal endite, spiniform endites with few or no auxiliary spines) are not preserved, and so this specimen is left in open nomenclature and not identified to the family level.Notably all radiodont appendages that are known from the Spence Shale have been assigned to Hurdiidae.A single body specimen from which frontal appendages are unknown was assigned to Anomalocaris Whiteaves, 1892 (Briggs et al., 2008, fig. 1), however following the vast number of new radiodont taxa described since then, the exact taxonomic placement of this specimen within Radiodonta is unclear.Given that amplectobeluids and anomalocaridids are known from both older and younger deposits in the Great Basin (e.g., Lerosey-Aubril et al., 2014, 2020a;Pates et al., 2021b), it might be expected that representatives of these families will be discovered in the future, and are lacking due to their rarity in Laurentian deposits of Wuliuan age and younger, rather than truly absent.
Description.-KUMIP491057 is a euarthropod carapace with a vase-shaped outline (Fig. 6).It measures ∼23 mm along its long axis, and ∼9 mm at the widest point perpendicular to the long axis (in dorsal view).The posterior part of the nuchal region and anterior part of the carapace are not preserved.The nuchal region is ∼3 mm wide.The carapace element then broadens to its widest point at approximately one-third of the distance from the nuchal region to the anteriormost preserved point.
The carapace then narrows anteriorly, with the outline changing from concave to convex at approximately two-thirds of the distance from the nuchal region to the anteriormost preserved point (Fig. 6, arrows).Relief is highest in the main region (Fig. 6, mr), with slender lateral extensions (Fig. 6, le) delineated by faint lines parallel to the long axis.On the left side of the element, these lines are associated with near-parallel compression wrinkles.
Remarks.-The specimen is likely a radiodont, and the vase-shaped outline and apparent relief allows this specimen to be tentatively identified as a hurdiid central carapace element.This specimen displays features comparable to a number of different hurdiid radiodonts, however the differences indicate that if a hurdiid affinity is confirmed, it most likely represents a new genus and species or belongs to a hurdiid for which the carapace is currently unknown, e.g., Buccaspinea.
The identification of a nuchal region (known in hurdiids, e.  Pates et al., 2021a).A change in outline from convex to concave is also known in Cordaticaris and Hurdia (Daley et al., 2013;Sun et al., 2020).However, in these two genera, this change in slope occurs very close to the distal tip of the carapace, not one-third of the distance from the tip as in KUMIP 491057.
Although the morphological features above support a hurdiid affinity for this euarthropod carapace element, a positive assignment to Hurdiidae, or indeed Radiodonta, requires the recognition of associated radiodont elements, e.g., frontal appendages, oral cones, or other body parts.Caution is warranted Thorax 10 mm long and up to 7 mm wide, composed of seven tergites (Fig. 7, T1-T7), each ∼7 mm wide and 3 mm long.Anterior part of each tergite partially concealed by tergite in front of it and spineless.Posterior part preserving short, thickbased, dorsally projecting sagittal spine.
Center part of pygidium not preserved.Pygidium 2 mm long and 3 mm wide, not including posterior spine, appearing to be composed of three nonarticulated tergites similar in morphology to those of thorax based on presence of three pygidial sagittal spines.Two anterior pygidial sagittal spines extending dorsally, slenderer and shorter than thoracic ones, whereas third spine hypertrophied, straight, and projecting posteriorly.
Posterior spine approximately same length (12 mm) as thorax and pygidium combined (12 mm), appearing to be mostly complete; particularly thick proximally, but gently narrowing distally until reaching approximate half of its proximal diameter at distal tip.
Material.-KUMIP314201, an almost complete specimen in lateral view.
Description.-Valvesubovate in outline; posterior portion moderately wider than anterior, with maximum width approximately two-thirds along length of hinge line from anterior margin.Maximum length 41 mm, maximum width Remarks.-Althoughvalves and complete carapaces of Perspicaris?dilatus are relatively common, YPM IP 530101 is the only known specimen to contain soft tissues (black film) possibly representing the animal being protected by said valves.Unfortunately, the preservation does not allow for a conclusive assessment, because no segments or other morphological information are preserved.The specimen is conspecific with Perspicaris?dilatus based on the outline of the valve (Fig. 8.2) with the maximum width being near the posterior end, and the relatively large posterior process.The shape also fits within the variation of the Perspicaris?dilatus valves from the Rockslide Formation (Kimmig and Pratt, 2015).The valve overlies a Marpolia sp.specimen (Fig. 8.1).
Diagnosis.-As for species.
Remarks.-Two valves are placed in Branchiocaris pretiosa because of their semicircular outline and the size and positioning of the anterior and posterior processes similar to previously described specimens of Branchiocaris pretiosa, which occurs in strata of approximately the same age (Briggs, 1976;Briggs and Robison, 1984).These are the first specimens of Branchiocaris pretiosa from the Spence Shale.Although the specimens do not preserve soft tissues, the valve of Branchiocaris pretiosa is fairly unique in its outline among carapaces of Cambrian arthropods and differs from Perspicaris?dilatus and Dioxycaris argenta in the smaller processes, the anterior process that is slightly smaller than the posterior process, and the semicircular rather than subovate to subelliptical outline of the valve.
Diagnosis.-Tuzoia with ovoid amplete to slightly postplete/ preplete outline (mean L:H 1.45, N = 47, specimens in lateral aspect clearly showing ventral margin).Carapace length 20-120 mm; mean length ∼77 mm (N = 47, SD = 16.5).Dorsal margin straight to slightly convex.Anterior cardinal processes broad-based, very short, not pointed, directed slightly downward.Well-developed anterior notch.Posterior cardinal processes Blunt, very small.Midposterior spine and posteroventral spine present, but very short.Midposterior spine often longer than posteroventral spine.One additional marginal spine between midposterior spine and posteroventral spine present or not.Posterior cardinal angle ∼110°.No dorsal spines.Low-relief lateral ridge running almost parallel to dorsal margin (H:A ∼2.0) underlined by very narrow frill with very small crenulation.Reticulate pattern dense, uniform, very small along anterior, posterior, and dorsal margins.Juvenile morphology similar to that of adults.(Vannier et al., 2007) Occurrence.-KUMIP 561726 originates from the Cycle 3 'Kootenia Quarry' of the Wuliuan Spence Shale Member Description of new material.-KUMIP561726 represents a partial single valve in lateral view.Only approximately half of the anterior part of the specimen is exposed and the posterior part is covered.The exposed part of the specimen is 48 mm long and ∼ 41 mm in height at its widest point.The anterior cardinal process is exposed and projects 2 mm from the anterior margin at an angle of ∼105°.The exterior surface is covered by somewhat irregular reticulate pattern of fine carbonaceous lines surrounding slightly convex interiors.The specimen preserves compaction wrinkles in the center of the valve, suggesting this area was vaulted in life.
New material.-KUMIP561726, partial right valve in lateral view.
Remarks.-Tuzoia retifera was previously known from a single specimen (KUMIP 153918) in the Spence Shale.This new specimen might represent a mostly complete valve, but preparation attempts were unsuccessful and, as such, the above description is based on the exposed part of the specimen.The specimen is assigned to Tuzoia retifera based on the exposed outline of the valve, the angle of the anterior cardinal process, and the somewhat irregular reticulate pattern of fine grooves surrounding slightly convex interiors covering the exterior surface of the valve.The pattern on the exterior surface of the valve is reminiscent of the pattern exhibited by Tuzoia guntheri (see Kimmig and Pratt, 2015).
Diagnosis.-Tuzoia with ovoid, slightly postplete outline (L:H 1.35 in holotype).Length (exclusive of spine) can exceed 80 mm.Dorsal margin straight to slightly convex.Anterior cardinal processes pointing straight forward, overhanging notch.Posterior cardinal processes shorter than anterior cardinal processes, directed upward and backward.At least two dorsal spines (one large and subvertical), both inserted along anterior third of dorsal margin.Posteroventral spine long, slender.Midposterior spine short.Two additional marginal spines present: one, very small, dorsal of midposterior spine; the other, longer, ventral of posteroventral spine.Lateral ridge with low relief, running obliquely (H:A ∼3.0 at valve midlength in holotype).Reticulate pattern over entire lateral surface.(Vannier et al., 2007) Occurrence.-KUMIP 561725 originates from the Cycle 3 'Kootenia Quarry' of the Wuliuan Spence Shale Member (Glossopleura walcotti Biozone) of the Langston Formation, Miners Hollow locality (GPS: 41.602, -KUMIP 561725 (Fig. 9.3, 9.4) is 120 mm long and 77 mm wide and preserved as part and counterpart.The valve has four spines on the posterior margin; the most dorsal 5 mm long, the midposterior spine 5 mm long, the posteroventral spine 10 mm long, and the ventral spine 2 mm long; and two dorsal spines (Fig. 9.3), the more anterior of which is 4 mm long, and the more posterior one 2 mm long.The preserved part of the anterior cardinal projects 2 mm from the anterior margin at an angle of ∼110°.The posterior cardinal process projects 2 mm from the posterior margin at an angle of ∼110°.Dorsal margin straight.
KUMIP 314036 (Fig. 9.4) is 165 mm long and 115 mm wide.None of the spines are preserved, but the outline of the valve corresponds to the outline of Tuzoia guntheri.The anterior cardinal process projects 2 mm from the anterior margin at an angle of ∼110°.
Remarks.-Tuzoia guntheri has been previously reported from the Cambrian (Wulian to Drumian) of the Great Basin and the Drumian Rockslide Formation of northern Canada (Robison and Richards, 1981;Liebermann, 2003;Vannier et al., 2007;Kimmig and Pratt, 2015), but this is its first record in the Spence Shale.
KUMIP 314036 preserves groove-shaped, simple burrows between 1 and 3 mm wide and several centimeters long (Fig. 9.2).Bifurcation is observed in a few instances, but likely due to intersection rather than true branching.They resemble the structures described from below panarthropod valves in other BST deposits (Zhang et al., 2007;Mángano, 2011;Mángano et al., 2012;Kimmig and Pratt, 2016) and are closest in shape and size to those described on valves of Perspicaris?dilatus from the Drumian Ravens Throat River Lagerstätte of northern Canada (Kimmig and Pratt, 2016).
Order and Family uncertain Genus Dioxycaris Gürich, 1929 Type species.-Lerpeditiaargenta Walcott, 1886.Kimmig et al.-New soft-bodied panarthropods from the Spence Shale Circular muscle scar inconspicuous in larger valves; located on smaller specimen (Fig. 10.3) close to anterior margin and three times its diameter from hinge line.
Remarks.-Dioxycaris argenta is the most common bivalved panarthropod in the Spence Shale, however the valves and carapaces seemingly have a tendency to decompose more rapidly than those of other bivalved panarthropods.Although this might have to do with varying taphonomic conditions in different Spence Shale outcrops (Whitaker et al., 2022), it also suggests that the valves might have been thinner than those of other bivalved panarthropods.With the specimens described herein, there are now at least nine specimens known from the Spence Shale, five of them from Antimony Canyon.This value likely underestimates the relative abundance of this taxon, because many fragmentary specimens from the Spence Shale doubtless represent fragments of D. argenta.
Order Bradoriida Raymond, 1935 Family uncertain Genus Walcottella Ulrich and Bassler, 1931 Type species.-Walcottellaapicalis Ulrich and Bassler, 1931 from the middle Cambrian of the Grand Canyon, Arizona, USA.
Figure 11.1-11.4 Occurrence.-KUMIP 579390 originates from + 5 m from the base of the exposed Wuliuan Spence Shale Member (Glossopleura walcotti Biozone) of the Langston Formation, Spence Gulch locality (GPS: 42.306, Remarks.-Thevalve and the trilobite were likely digested and are part of a coprolite or regurgitite that appears to have lost its soft parts.Coprolites are common in the Spence Shale (Kimmig and Strotz, 2017) and bradoriid shells have been identified in coprolites from other deposits (Kimmig and Pratt, 2018).
Description.-Dorsoventrallycompressed, 9.8 mm long (reconstructed pre-disarticulation), preserving cephalon and trunk (partly separated, with greatest degree of separation on right side of specimen).Cephalic shield ovoid in outline, 4.9 mm long, 3.9 mm at widest point 0.5 mm from posterior end.Left portion of cephalon broken off, separated from main body of cephalon (Fig. 12).Genal angles rounded, spineless.Narrow marginal rim preserved on sides of cephalon.One cephalic appendage pair preserved at posterior end of cephalon, partly overlapped by cephalic shield and oriented posteriorly.Partial left antennule appears to be preserved.
Trunk elongated, suboval in outline, 4.9 mm length, 3.8 mm at widest point 1.6 mm from anterior end.Median keel apparent and appears to run entire length of pygidium, 0.4 mm at widest point.Faint marginal rim, 0.2 mm wide, borderng pygidium.
Three appendage pairs apparent on each side of specimen with same morphology as preserved cephalic appendages; right side appears to preserve exopods in addition to endopods.These angled posteriorly, with those on left side more completely preserved.Longest limb, occurring most posteriorly on left side, 1.7 mm length, 0.2 mm at its widest point.Remarks.-Preservation of this specimen is poor, and it appears to be a molt because left part of the cephalon is partially broken off.The specimen preserves sufficient anatomical detail-including the subequally divided dorsal section, the single transverse articulation between the cephalon and the trunk, and the narrow marginal rim of the cephalon-that it can be attributed to Naraoia? sp.indet.The specimen is considered to likely belong to Naraoia also based on the dorsal carapace being divided into two subequal parts that are separated by a single transverse articulation.

Discussion
Panarthropods are by far the most diverse group of animals in the Spence Shale and the new material adds 10 species, bringing the total diversity to 67 species.This makes the Spence Shale the second most diverse panarthropod fauna of the Cambrian of Laurentia, only surpassed by the Burgess Shale of Canada.Unsurprisingly, the most abundant and diverse panarthropods in the Spence Shale are radiodonts and bivalved panarthropods, but the distribution of these two groups differs.So far, radiodonts are restricted to the shales of the Wellsville Mountains, whereas bivalved panarthropods are also found at the High Creek and Spence Gulch localities, in shallower water carbonates (Maxey, 1958;Liddell et al., 1997;Kimmig et al., 2019b;unpublished data, Kimmig, 2021).This difference in distribution could have several explanations: (1) it might be that hurdiid radiodonts preferred deeper-water environments, an explanation indeed offered for their rarity in early Cambrian deposits (Wu et al., 2022); (2) there could be taphonomic factors that allowed radiodonts to be preserved in the Wellsville Mountains strata that were not present at other localities (Whitaker et al., 2022);or (3) this could be due to collection biases, because the Wellsville Mountains localities have been extensively excavated, whereas the other localities have not been sampled to the same extent (Whitaker and Kimmig, 2020).This difference in distribution also applies in general to the abundance of panarthropod and other species in the Spence Shale, because the Wellsville Mountain localities, especially Antimony Canyon and Miners Hollow, are the only known localities for many of the species described (Conway Morris et al., 2015;Legg and Pates, 2017;Kimmig et al., 2019b;Whitaker and Kimmig, 2020).
The soft-bodied panarthropod fauna was previously thought to be limited to the Spence Shale in the Wellsville Mountains and the material presented herein demonstrates that this is definitely not the case.It is now apparent that soft-bodied panarthropods can be preserved in all of the environments present in the Spence Shale, from the shallower-water carbonates of High Creek and Spence Gulch, to the more distal deposits of Two Mile Canyon.

Conclusions
The Spence Shale preserves a unique panarthropod fauna in the Miaolingian of Laurentia, because radiodonts are the most abundant soft-bodied panarthropods, comprising approximately one-third of the identified specimens (Fig. 13).Most of these specimens are hurdiids.Additionally, the Spence Shale not only preserves arthropod species that are found in the Wuliuan-age Burgess Shale of Canada, i.e., Branchiocaris pretiosa, Dioxycaris argenta, Thelxiope cf.T. palaeothalassia, and Tuzoia retifera, but also species that are otherwise confined to the Drumian deposits of Laurentia, i.e., Buccaspinea cooperi Pates et al., 2021a and Tuzoia guntheri.
The new panarthropod specimens described herein also provide additional information on the distribution of soft-bodied taxa in the Spence Shale and suggest that other exposures beyond those currently sampled might also preserve soft-bodied fossils.For instance, most of the collecting in the Spence Shale has been done in the Wellsville Mountains (Whitaker and Kimmig, 2020), and thus, the majority of soft-bodied fossils are known from this region (Kimmig et al., 2019b;Whitaker and Kimmig, 2020).It might be that much of the diversity of the Spence Shale remains to be discovered, and species currently known from one or a few specimens-e.g., Armilimax Kimmig and Selden, 2021, Shaihuludia Kimmig et al., 2023, Siphusauctum O'Brien and Caron, 2012(see Kimmig et al., 2017), Utahscolex Whitaker et al., 2020, and Totiglobus Bell and Sprinkle, 1978(see Wen et al., 2019b)-might be more abundant than previously thought.

Figure 1 .
Figure 1.Locations of the Spence Shale Lagerstätte: (1) map of the western USA showing the location of the Spence Shale; (2) geological map (based on the USGS state maps for Google Earth Pro) of northern Utah and southern Idaho showing the principal localities within the Spence Shale; (3) simplified stratigraphy of the Langston Formation.AC, Antimony Canyon; BF, Blacksmith Fork; CC, Cataract Canyon; CFC, Calls Fort Canyon; DH, Donation Canyon; EC, Emigration Canyon; HC, Hansen Canyon; HCR, High Creek; MH, Miners Hollow; ON, Oneida Narrows; PP, Promontory Point; SC, Smithfield Creek; SG, Spence Gulch; TMC, Two Mile Canyon.

Figure 4 .
Figure 4. Jitter plot showing ratio of endite length to podomere height for published Buccaspinea and Hurdia appendages, alongside appendages recently tentatively reassigned to Buccaspinea? by Pates et al. (2021a), and those described in this contribution.Proximal two endites and associated podomeres measured for each specimen.Numeric values for ratios and sources for published images are provided in Table2.
g., Cordaticaris and Pahvantia; Lerosey-Aubril and Pates, 2018; Sun et al., 2020) allows the anteroposterior axis of the Kimmig et al.-New soft-bodied panarthropods from the Spence Shale 9 https://doi.org/10.1017/jpa.2023.24Published online by Cambridge University Press carapace to be identified.The widest part of the carapace is closest to the posterior, as in all hurdiid central carapace elements.The slender outline of KUMIP 491057 is similar to that known in Aegirocassis, Hurdia victoria Walcott, 1912, and Pahvantia, and contrasts with the broad central elements of Cambroraster, Cordaticaris, and H. triangulata Walcott, 1912.However, the specific shape of the outline differs.A nuchal region (identified in KUMIP 491057, present in Pahvantia) is unknown in Aegirocassis and H. victoria.However, although the presence of lateral extensions separated from the main region by faint lines is also known in Pahvantia (Lerosey-Aubril and Pates, 2018), KUMIP 491057 lacks the prominent ocular notches and associated spines described for Pahvantia (Lerosey-Aubril and Pates, 2018; Lerosey-Aubril et al., 2020a;

Figure 6 .
Figure 6.Radiodonta? (KUMIP 491057) collected by the Gunther family from the Antimony Canyon locality, Spence Shale, Langston Formation (Cambrian: Wuliuan), Utah, USA: (1, 2) possible central carapace element of a hurdiid radiodont in dorsal view and explanatory drawing.le, lateral extension; mr, main region; nr, nuchal region.Arrows indicate change in slope of outer margin from concave to convex.

Table 1 .
Radiodont specimen fragments reported from the Spence Shale, Langston Formation (Cambrian: Wuliuan), Utah, USA.Specimens described in this contribution in bold font.

Table 2 .
Specimens , references, figure numbers, and generic assignments for ratios of endite length to podomere height visualized as jitter plot in Figure4.Only proximal two endites were measured for each specimen.* = same specimen measured multiple times because it was figured in multiple studies.Specimen numbers reproduced as written in original publications.
Ulrich and Bassler, 19311997) mm length, 8 mm width, ovate in outline.Hinge line well-developed, midanterior surface showing marked indentation, possibly indicative of single anterior lobe.Faint furrow demarcating a moderately wide margin.Remarks.-Allthreespecimensareflattenedand show signs of weathering.KUMIP 579390 and 579391 are partially obscured by matrix and overlapping nondescript skeletal elements.The valve outline is more symmetrical than that of Anabarochilina cf. A. australis Hinz-Schallreuter, 1993, described from the Cambrian Marjum and Weeks formations of Utah, and Liangshanella burgessensis Sieveter and Williams, 1997 from the Burgess Shale of Canada(Sieveter and Williams, 1997).However, the outline and the position of the possible anterocentral node is similar to that of Walcottella apicalisUlrich and Bassler, 1931from the Cambrian (Wuliuan) Bright Angel Shale of Arizona.For these reasons, we tentatively assign these specimens to Walcottella.It is worth noting that the Bright Angel Shale specimens are preserved in three dimension and these specimens are flattened.