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


745


Figure 7. Detailed morphology and preservation of Moroccodiscus smithi n. gen. n. sp. showing the marginal ossicles and radial ducts. (1–5) rectangular- to trapezoidal-shaped marginal ossicles with one or two radial ducts; the latter ossicles are normally wider and/or trapezoidal. (1) Paratype UCBL-FSL 712000; (2) paratype NPL 62451; (3) paratype NPL 74385; (4) paratype UCBL-FSL 712000; (5) paratype NPL 74386. (6) Both types of marginal ossicles showing the radial duct openings; paratype UCBL-FSL 712000. (7–9) Partial marginal rings with steinkern fillings of radial ducts and molds of cupule-like cavities and frontal plates. (7) Holotype UCBL-FSL 712001; (8) paratype NPL 74386; (9) paratype UCBL-FSL 712000. (1–3, 7–9) Photographs of moldic specimens whitened with ammonium chloride sublimate. (4–6) Digitally reconstructed CT images. Scale bars = 5mm.


Alnif, eastern Anti-Atlas Mountains, southeastern Morocco, North Africa (see Rábano et al., 2014; Zamora et al., 2015). All known specimens of this cyclocystoid appear to have come from this same thin interval, although the locality has been given several different names by different collectors (30.639525°N, 005.104275°W; 30.92025°N, 005.25339°W; and 30.55223°N, 005.15240°W).


Description.—Most specimens nearly circular, holotype very slightly subpentagonal, axially compressed, many specimens slightly convex on one side, nearly flat or slightly concave on the other side. Most of relief in studied molds located in ring of thick marginal ossicles. Central disk, frontal plates, and peri- pheral skirt very thin, easily damaged, and more difficult to interpret.


Central disk (Fig. 6): thin, domed, nearly circular area


about 61mm wide in holotype (about 68% of thecal diameter), about 20mm wide in smaller paratype NPL 62451A (about 50% of diameter); composed of two tightly appressed, thin layers, upper layer of slightly imbricate (toward center), small


(flooring?) plates, each bearing a central, shallow, radiating food groove with elongate pores laterally between plates; lower layer has more rounded pores within polygonal annular plates: two arc-shaped areas near outer margin of disk more disrupted, tilted up, and more clearly imbricate in scans (Fig. 6.1–6.6). Food grooves shallow, difficult to see, in some places marked by plated ‘rays’ between radiating lines of pores, cover plates on food grooves very small and cryptic, not usually seen; mouth small, usually near center of disk; folded paratype NPL 74386 (Fig. 3.12, 3.13) has small mouth opening partly exposed in fused area (oral frame?) with converging food grooves about one-third its diameter; periproct not seen, possibly lateral. Marginal ossicles (Figs. 7, 8.1): Holotype having complete


circlet of 54 large, rectangular to trapezoidal, thick ossicles with total of 68 radial ducts (Figs. 3.1, 3.2, 7.7, 8.1); smallest paratype NPL 62451 having nearly complete circlet of 33 large ossicles interrupted by about 9 stunted ossicles (Figs. 3.8, 3.9, 4.1, 4.2, 9.7) with total of about 54–55 radial ducts; ossicles with one radial duct nearly rectangular, longer than wide (3.8– 3.9mmlong, 2.2mmwide), nine of these ossicles slightly wider


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