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Journal of Paleontology 91(4):604–617


comes from its early stratigraphic position, the hydropore and gonopore openings not being incorporated into the plating of the ambulacral system, the complex system of adradial and abradial ambulacral floor plates, and the multitiered cover plates (Zhao et al., 2010). Vestiges of each of these characters can be seen in more derived pentaradiate taxa, though it is the least clear in Eleutherozoa, where subsequent character evolution erased most of the data from the mouth frame. In Kailidiscus, the mouth frame is bordered by two plate


series—the precursor plates to the oral frame plates and interradially positioned oral plates (termed integrated interradial plates in Zhao et al., 2010). The precursor oral frame plates are


an adradial set of floor plates along the ambulacral midline that is bordered by an abradial set of floor plates to the sides (Zhao et al., 2010) (Fig. 2.1, 2.2). Both sets of floor plates contribute to the wide food groove and bear podial pores. The adradial floor plate set meets along the midline biserially and bears two abradially


multielemental and form a continuous series with the adradial floor plate system (Fig. 2.1, 2.2). These plates are proximal to the oral plates and form the edge of the peristomial opening. The oral plates lie interradially, immediately distal to the precursor oral frame plates. They are broadly exposed on the thecal exterior, as in nearly all oral-plate-bearing taxa. Furthermore, they bear podial pores along their proximal sutures with the precursor oral frame plates and form a continuous series with the abradial floor plate system both positionally and morpho- logically (Fig. 2.1). Oral plates O1 and O6 are clearly present in the CD interray; O7 is possibly present, though this is somewhat unclear in the available material (Fig. 2.2). The floor plate system of Kailidiscus is quadruserial, bearing


positioned prongs that contact each of two adjacent abradial floor plates. These prongs form the edges of each of three podial pores—two adradial pores that are laterally positioned and one abradial pore that is medially positioned (Fig. 2.1). These plates are fully internal and cannot be seen externally on the theca (Fig. 2.2) exceptwhere theywrap around the proximal edge of the


articulating to similar prongs on the adradial floor plates forming the border of three pores—two abradial pores laterally and one adradial pore medially (Fig. 2.1). The abradial margin of the abradial floor plates is broadly expressed externally along the ambulacral margin (Fig. 2.2). The cover plates on Kailidiscus are unusual and similar to other Cambrian taxa such as helicoplacoids and cinctans (Zhao et al., 2010, figs. 6, 8). They are broadly generalized and bear several tiers of plates that decrease in size medially though in repeating cycles. No PPCPs are differentiated or recognizable in this taxon.


Discussion.—Two separate pathways are seen in the evolution of pentaradiate echinoderms with respect to the axial skeleton. The first centers on the oral frame plates and adradial floor plates (Type B peristomial borders of Kammer et al., 2013). This includes some Cambrian eocrinoid-grade echinoderms and some derived edrioasteroids. From the thecal interior, this morphotype is recognized by the radial position of the peristomial border plates. From the exterior, it is recognized by a lack of broad expression of peristomial border plates interradially and the lack of expression of the floor plates along the edges of the ambulacra. The second pathway centers on the oral plates and


the abradial floor plate series. This includes derived blastozoans and crinoids (Type A peristomial borders of Kammer et al., 2013). This morphotype is recognized internally by the interradial positioning of the peristomial bordering plates. From the exterior, it is recognized by the broad expression of the interradial peristomial bordering plates and the broad expression of the floor plate bodies along the edges of the ambulacra.


orals. The abradial floor plate set lies abradially to the adradial floor plates extending along both lateral margins. These plates show a 1:1 correspondence with the adradial floor plate set. Abradial floor plates bear two prongs extending adradially,


Plesiomorphic edrioasteroids.—Edrioasteroids are a para- phyletic assemblage of globular to discoidal echinoderms that have recumbent ambulacra incorporated into the body wall and lack free brachioles or ambulacral extensions above the theca. Many of the Cambrian forms are difficult to interpret because the bottom surface of the theca is plated, covering information about the mouth frame and floor plates. Some taxa such as Cambraster and Stromatocystites have large interradial oral platesmuch like Kailidiscus (Zamora et al., 2013b,


Figure 2. Colorized photographs showing the distribution of plate types on pentaradiate echinoderms. (1, 2) Internal and external views of the Kailidiscus chinensis paratype GM2103, showing the plating of the peristomial border and ambulacral floor plate system. Red plates are the oral plates; green plates are the abradial floor plates; light blue plates are the adradial floor plates; purple plates are the precursor oral frame plates. Note that in the distal ambulacra, only the abradial floor plates can be seen outside the food groove but are visible because the cover plates in yellow are taphonomically stripped from most of the specimen. (3)Interiorviewof the eocrinoid-grade echinoderm Lepidocystis wanneri Foerste, 1938 MCZ628 showing radial oral frame plates in purple and adradial floor plates in light blue. (4) The oral area of Lepidocystis wanneri GTBM95265 showing radial oral frame plates in purple. Brachioles mount at the ambulacral tips. (5) Interior view of the sorophinid Anedriophus moroccoensis Sumrall and Zamora, 2011, FSTG/AA-BCBb-OI-25. Radial oral frame plates in purple lead to uniserial adradial floor plates in light blue. Primary peristomial cover plates in blue and cover plates with podial basins and intrambulacral canals in yellow cover the food groove. (6) The parablastoid Eurekablastus ninemilensis Sprinkle and Sumrall, 2008 1781TX5 showing abradial floor plates in green and oral plates in red. Primary peristomial cover plates in blue and ambulacral cover plates in yellow cover the ambulacra. (7, 8) Exterior CMCIP 40480 and interior CMCIP 40478 view of Edriophus levis. Oral plates in red and abradial floor plates in green are visible from exterior while oral frame plates in purple can only be seen from the interior. Primary peristomial cover plates in blue and ambulacral cover plates in yellow cover the ambulacra. (9) Detail of the diploporitan Eumorphocystis multiporata Branson and Peck, 1940 SUI97599 showing the construction of the ambulacrum. Abradial floor plates in green are in contact with extraxial plates in pink arising from single ‘radial plate’ in black– note filler plates in light yellow and large lumen proximally. Cover plates and brachioles are in dark yellow. (10) Lateral view of Lipsanocystis rugosus Stumm, 1955 UMMP 31432 showing double biserial outer floor plates in green and light green. Oral plates are in red. (11) Summit view of Eumorphocystis multiporata SUI97598 showing abradial floor plates in green and oral plates in red. Primary peristomial cover plates in blue and ambulacral cover plates in yellow cover the ambulacra. (12, 13) Oral views of the eocrinoid grade echinoderm Rhopalocystis destombesi Ubaghs, 1963 without PMO A29122 and with PMO A29124 cover plates. Oral plates in red lead to abradial floor plates in green. Primary peristomial cover plates in blue and ambulacral cover plates in yellow cover the ambulacra. (14) The crinoid Neoplatycrinus dilatatus Wanner, 1916 SUI 134856 showing greatly enlarged primary peristomial cover plates in blue and ambulacral cover plates in yellow. (15) The crinoid Collicrinus yandelli Owen and Shumard, 1850 USNM S1337 showing greatly enlarged primary peristomial cover plates in blue and ambulacral cover plates in yellow. (16) The crinoid Nuxocrinus crassusWhiteaves, 1887 USNM 305473 showing greatly enlarged primary peristomial cover plates in blue and ambulacral cover plates in yellow. Scale bars = 5 mm. (1–5, 7, 8, 11–16)Modified from Kammer et al. (2013); (6, 9, 10)new.


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