Pates et al.—Hurdiids from the middle Cambrian of Utah
Hurdiids from the Wheeler Formation.—Hurdia is known from theWheeler Formation by a single P-element. Peytoia is known from one appendage and several mouthparts. KUMIP 153901a/b (Fig.5.6,5.7)was first described by Robison and Richards (1981, pl., 4, fig. 1a, b) as Proboscicaris agnosta, which at the time was thought to be a phyllocarid. Proboscicaris is now identified as the P-element of the Hurdia carapace (Daley et al., 2009). KUMIP 314086a/b (Fig. 5.1, 5.2) was first described by Briggs et al. (2008, fig. 2.2) as a radiodontan appendage. Owing to the relatively limited preservation, they did not classify it to genus. It is an appendage with 10 podomeres, with elongated ventral spines on podomeres 2–6. Six auxiliary spines are present perpendicular to the ventral spine of podomere 5. There are three small triangular terminal spines on podomere 10. The presence of three terminal spines, the orientation of ventral spines, and the curved distal end indicate it is a Peytoia appendage. Conway Morris and Robison (1982, text-fig. 1, pl. 1, figs. 1–5) described two specimens,KUMIP 153093a/b (Fig. 5.10, 5.11) andKUMIP 153094 (Fig. 5.5), of radiodontan oral cones as Peytoia cf. P. nathorsti, and we support this interpretation because of the overall arrangements of plates and the lack of tooth rows inside the main opening. The genuine absence of additional rows of teeth can be confirmed by examining the central opening, which is well preserved. KUMIP 314078 (Fig. 5.8, 5.9), first described by Briggs et al. (2008, fig. 2.2), is an oral cone with four large plates and seven smaller plates between each pair of larger plates. Part of themouth apparatus is not preserved, but it can be inferred that it had 32 plates (four large, 28 small) radially arranged. The central opening of the incompletemouth apparatus does not have additional tooth rows, so it can be identified as Peytoia. Conway Morris and Robison (1988, fig. 26.3) identified
KUMIP 204781a/b (Fig. 5.3, 5.4) from the Wheeler Formation as a P. nathorsti appendage. A previous taxonomic analysis (Daley et al., 2013a) suggested that this was potentially a Hurdia appendage. As the distal end of the appendage is not preserved and the morphology of the ventral spines is not conclusive, it is identified here as a hurdiid, but no identification to the genus level is made.
Peytoia from the Marjum Formation.—Hurdia is not known from the Marjum Formation. Briggs and Robison (1984) iden- tified USNM 374593 (Figs. 6, 7) from the Marjum Formation as a partial body (lacking frontal appendages) of Peytoia nathorsti because of the presence of transverse lines on the flaps. These had only been observed in P. nathorsti and not Anomalocaris canadensis, which at the time was the only other radiodontan body type known. We support placement in Peytoia because of the presence of large posterior-tapering swim flaps (in contrast to the small flaps of Hurdia) with transverse lines (which are absent in Anomalocaris) and the absence of a tail fan (present in Hurdia and Anomalocaris). The specimen consists of the 11 most posterior segments and tail of the animal, with flaps and central body structures preserved together. There is slight overlap of the anterior and posterior edges of the flaps and the
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presence of some high-relief mineralized structures (Fig. 7). A dark brown-grey linear structure (‘ba’ in Fig. 6.5) runs down the median axis of the animal, 6–7mm wide near the anterior,
tapering to a point and disappearing as it reaches the pair of body flaps. This region has a very thin (1mm wide) feature at its midline running along the length of the body, particularly visible in the counterpart (‘g’ in Fig. 6.5). This is interpreted to be the gut running through the body cavity. It is flanked on both sides by a series of bilaterally symmetrical dark grey features (‘s1–s11’ in Fig. 6.5). They are larger anteriorly (3× 25mm) than posteriorly (1.5 ×10mm) and are interpreted as setal blade blocks because of their preservation, position, and co-occurrence with body flaps. Lateral to the setal blade structures, and partly overlapping them, there is a series of dark reflective structures with high relief, present in the region where the base of the flaps meets the axial region (‘m1–m6’ in Fig. 6.5). These structures are interpreted as musclulature because of similarities between them and musculature in
Anomalocaris canadensis (Daley and Edgecombe, 2014, figs. 15, 17). Both have a fibrous texture (Fig. 7.3–7.5), are
similar in size and shape (Fig. 7), and are at the base of body flaps (Fig. 7.1, 7.2). In A. canadensis, these structures are pre- served as an orange material or as a high-relief dark grey to black reflective material. In Peytoia (USNM 374593), they are similarly preserved as high-relief dark reflective material, although the fibrous details are less well preserved than in A. canadensis (compare Fig. 7.3, 7.5 to Fig. 7.4). They are not interpreted as gut diverticulae, which are often preserved as high-relief dark reflective material, as they do not intersect the
gut and are instead associated with the intersection of the body flaps with the cuticularized body, far from the body axis. However, it must be noted that euarthropod gut diverticulae are preserved in a variety of ways (Lerosey-Aubril et al., 2012), and the preservation of this musculature is different from muscu- lature reported from some other Burgess-Shale type localities: Pambdelurion from Sirius Passet (Budd, 1998) and Myoscolex from the Emu Bay Shale (Briggs and Nedin, 1997). The second most anterior flap on the right side of the
counterpart preserves a set of high-relief linear structures near its base, located between the musculature of this flap and the flap in front of it (Fig. 6.4, ‘st’ in Fig. 6.5). The six parallel, evenly spaced structures are mineralized, and although they are closely packed, they do not touch one another. The longest one, closest to the body axis, is just under 1mm in length, and the structures become shorter away from the body axis, with the shortest one just under 0.5mm in length. Two millimeters below the linear structures, there are a number of circular mineralized structures, around 0.25 to 0.5mm in diameter. Small spheres 0.5mm in diameter are present on other phosphatized blocks. Similar structures, which were identified as clusters of pyrite framboids, have been reported from the middle Cambrian (Series 3) Pioche Shale by Moore and Lieberman (2009). Transverse lines only cover the anterior portion of the flap (Fig. 6.3), and no internal structure of the flaps is preserved, similar to P. nathorsti from
Figure 5. Hurdiid appendages, oral cones, and carapace element from the Wheeler Formation, House Range, Utah, USA. (1) Appendage KUMIP 314086b; (2) KUMIP 314086a, part to 1;(3) appendage KUMIP 204781a; (4) KUMIP 204781b, counterpart to 3;(5) oral cone KUMIP 314094; (6) Hurdia P-element 153901a; (7) KUMIP 153901b, counterpart to 6;(8) oral cone KUMIP 314078b; (9) KUMIP 314078a, part to 8;(10) oral cone KUMIP 153093b; (11) KUMIP 153093a, part to 10. Scale bars = 10mm.
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