Allaire et al.—Early Ordovician eocrinoids from Morocco


radials (isolated plates or one circlet), and forming sometimes rows between laterals; the basal can be split; radials globular- shaped; thecal plates ornamented with continuous vermiculated folds. Stem composed of cylindrical columnals of different sizes, some of them more elongated and nodal-shaped (swollen).


Occurrence.—Late Tremadocian (A. victoriae Zone to H. copiosus Zone), Fezouata Shale, Zagora area, localities 809 (=1157 = 1725), 2367, Z-F1, and Z-F12c (Fig. 3), central Anti-Atlas (Morocco).


Description.—The theca of R. zagoraensis is relatively small (thecal length between 15 and 21 mm). It is made up of six principal circlets of plates. The basal circlet is generally com- posed of one plate, but this basal plate is sometimes split into two superposed elements (e.g., Figs. 14.19, 14.20, 15.12), which is unique within the genus Rhopalocystis. The infralateral circlet is composed of four plates, and the lateral circlet is composed of a variable number of plates between four and six. The radials are generally organized in three circlets. Numerous additional secondary plates can be intercalated between the six primary circlets of plates. Their shape, size, and organization are irregular. These intercalary plates can be located between infralaterals and laterals (e.g., Fig. 14.1–14.17, 14.19–14.21), and between laterals and radials (e.g., Fig. 14.1–14.4, 14.6–14.8, 14.10, 14.11, 14.13, 14.14). Some specimens also display additional rows of plates between laterals (e.g., Fig. 14.1–14.3, 14.8, 14.10, 14.11, 14.14). The additional skeletal elements located between infralaterals and laterals can be very numerous and form up to three circlets of plates. Usually, the additional plates located between laterals and radials are less numerous; they can consist of isolated plates or form one com- plete circlet. The size, shape, and organization of these sec- ondary plates are irregular, and they do not form continuous and well-defined circlets, but rather an irregular, disorganized pavement. The radials have a characteristic globular shape (almost


hemispheric) and usually constitute three circlets (e.g., Fig. 14.1–14.13, 14.15, 14.17, 14.20), but some individuals have four circlets of radials (e.g., Fig. 14.14), and some small specimens seem to have only two radial circlets (e.g., Fig. 14.18, 14.21) . R. zagoraensis is characterized by a typical ornamentation,


already described by Chauvel (1971, 1978) and consisting of continuous folds (Fig. 15). Indeed, thecal plates are ornamented with vermiculated ridges (folds), but this ornamentation is more or less pronounced among the individuals. In some specimens, the plates have only short vermiculated folds, whereas in others,


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the thecal plates have both small and long folds, which are continuous on several plates and meet at the center of the largest ones (infralaterals, laterals). This produces a characteristic pattern corresponding to vermiculate radiating ridges (Fig. 15.1–15.3, 15.5, 15.10, 15.14). Usually the radials also have ornamentation folds. Finally, in some specimens, this typical ornamentation (small vermiculated folds) is little pronounced (e.g., Fig. 15.4, 15.6–15.9, 15.12, 15.13, 15.15), and sometimes only the basal is vermiculated (e.g., Fig. 15.13). The extension and strength of the ornamentation are highly variable among individuals. This variability in the ornamentation can be observed at each locality. Plate boundaries can be bordered by numerous epispires, and they are sometimes difficult to identify in the most ornamented specimens because of the vermiculated ridges (e.g., Fig. 15.2, 15.4, 15.5, 15.8, 15.10, 15.14). In some specimens, the proximal part of the stem is


preserved in connection with the theca (e.g., Figs. 14.5, 14.6, 14.13, 15.7, 15.11, 15.12). It is made up of cylindrical columnals of various sizes; some of them are more elongated, swollen, and nodal-shaped. Apart from the globular shape of the radials, the


morphology of the oral surface of R. zagoraensis (e.g., Figs. 14.22, 15.16) is very similar to that of R. destombesi. The posterior interradial area can be observed in several specimens (e.g., Figs. 14.3, 14.4, 14.8–14.10, 14.12, 14.18, 14.20, 14.22, 15.4, 15.5, 15.9, 15.13, 15.15, 15.16); the organization of this area appears to be also comparable to that of R. destombesi. It is composed of a higher number of plates comparing with the other interradii, and the periproct is located at the same place, behind the anal protuberance (a plate with an important relief). The brachioles were not observed, but they are probably biserial and swollen at their base.


Materials.—Several latex casts of the original study material of Chauvel (1971, 1978) and Chauvel and Régnault (1986): the holotype 1725g and 1725b', c'1, f', h, h', i1, i3, i6–i8, i12, i16, i17, i19, j6–j8 (locality 809 = 1157 = 1725; Fig. 1) and 2367c1, c2, c3, d1, d2 (locality 2367; Fig. 1). Examined original samples include specimens 1725h'


(locality 809 = 1157 = 1725; Fig. 1), 2367c and d (locality 2367; Fig. 1), as well as numerous external molds of thecae from Z-F12c (Fig. 1): AA-TISa-OI-1-24 and UCBL-FSL 712.044. Two original samples with external molds of thecae and


isolated plates, coming from locality Z-F1 (Fig. 1): AA-TAM- OI-64 and 74.


Remarks.—In R. zagoraensis, the variability in the number of additional plates appears to reflect a growth allometry. Indeed,


Figure 13. Rhopalocystis havliceki, photographs of latex casts dusted with ammonium chloride. (1, 2, 6, 8–10) Locality Z-F1, late Tremadocian; (3–5, 7) locality Z-F12c; late Tremadocian (A. murrayi Zone); (11) locality 2082, Lower Ordovician. (1) Aboral part of theca, two radii are visible (AA-TAM-OI-7). (2) Fragment of a theca (lateral area), with both extremities missing (AA-TAM-OI-79). (3) Aboral part of theca; a part of the oral surface is preserved; two ambulacra are visible; each possesses eight brachioliferous plates (AA-TISa-OI-22g). (4) Theca with the aboral part missing; the ornamentation is clearly visible; some plates exhibit a central umbo; all plates possess small ornamentation folds that can be continuous from plate to plate (AA-TISa-OI-27a); an aboral fragment of theca belonging to another individual (AA-TISa-OI-27b, right side) is preserved above the theca of AA-TISa-OI-27a; two spine-shaped radials are visible. (5) AA-TISa-OI-26; (6) AA-TAM-OI-6a; (7) AA-TISa-OI-22e; (5–7) adoral part of thecae with the proximal part of stem preserved in connection with theca. (8) AA-TAM-OI-21a; (9) AA-TAM-OI-22; (10) AA-TAM-OI-9; (11) 2082a (specimen initially assigned to Rhopalocystis sp. C and figured by Chauvel, 1978, text-fig. 11o, p, pl. 5 fig. 4); (8–11) thecae partially complete; the aboral part is missing; the spine shape of some laterals is clearly visible; these plates seem particularly robust. Scale bar = 1 cm.


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