Reich et al.—First Ordovician cyclocystoid (Echinodermata) from Gondwana


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Figure 9. Detailed morphology and preservation of Moroccodiscus smithi n. gen. n. sp. showing the frontal plates and the peripheral skirt. (1–5) Digitally reconstructed CT images showing the elongate-trapezoidal trough-shaped frontal plates in different views; paratype UCBL-FSL 712000. (6–8) Small to tiny, imbricate plates (up to 15 rows) of the wide peripheral skirt in different views: (6) moldic holotype UCBL-FSL 712001 top view, not whitened; (7) moldic paratype NPL 62451 bottom view, whitened with ammonium chloride sublimate; (8) paratype UCBL-FSL 712000 bottom view, digitally reconstructed CT image. Scale bars = 5mm.


cyclocystoid species but will help in future discussions on higher-level systematics within the Cyclocystoidea. The elongate, concave frontals sutured to the sloping back


edges of the marginal ossicles, mostly under the distal overhang of these large domed plates, the ducts through these plates leading to radiating and distally branching food grooves on the domed central disk, and eventually leading to a central body opening (the mouth?), resembles the upward-facing food- gathering systems of other suspension-feeding echinoderms, such as edrioasteroids. Extending the distal edge of the marginal ossicles into an exposed concave structure and shortening the frontals and perhaps changing their function would produce the cupules found in most other Ordovician cyclocystoids. Some authors, such as Nichols (1969), considered that cupules housed large tube feet, whereas Smith and Paul (1982) believed that these distinct and obviously important skeletal structures were not associated with tube feet. From the partially visible pattern of ray branching in the holotype (UCBL-FSL 712001) and the possible mouth opening near the center of the folded central disk in paratype NPL 74386 of Moroccodiscus, we can assume that the mouth is also located near the center of the disk in all


specimens of this new species. The interior of the domed central disk has no basal plated surface extending in from the marginal ossicle ring in CT scan cross sections (Fig. 10.1, 10.2). We believe that cyclocystoids were sessile suspension feeders living directly on the seafloor, with the central disk upward and the soft parts protected below it (Sprinkle et al., 2015).


Radial versus interradial orientation in cyclocystoids


Cyclocystoids are nearly radially symmetrical with relatively little irregularity. The mouth appears to have been located in the center of the oral disk in the few specimens where it has been identified, and all the ambulacral grooves, if preserved, appar- ently lead to this point (Smith and Paul, 1982). The periproct has not been identified in cyclocystoids but, if present, was probably lateral in the posterior interray of the oral disk. The peripheral ossicles, however, do show some irregularity in Moroccodiscus and other genera. Because the ambulacra branch dichotomously (Fig. 8.2) during growth away from the central mouth, the marginal ossicles with their pores, cupules, and/or frontal plates


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