Allaire et al.—Early Ordovician eocrinoids from Morocco
(e.g., Figs. 2, 5.9, 5.14, 5.17, 7.2–7.9, 8.1, 8.2, 8.7, 8.9, 8.10). However, some individuals have one or more additional secondary plates. These additional elements can consist of isolated plates, localized between infralaterals and laterals and/or between the laterals and the first radial circlet (e.g., Figs. 7.11, 7.15, 7.16, 8.6). In some other specimens, these additional plates can form a circlet (complete or incomplete) between infralaterals and laterals (Figs. 5.11, 7.12, 7.14, 8.3, 8.5). Some specimens have two circlets of intercalary plates: one between infralaterals and laterals and one between the laterals and the first radial circlet (e.g., Figs. 5.10, 7.13, 8.4). The thecal length of the studied specimens varies from
12 to 50mm. Some individuals are particularly large (e.g., Figs. 7.1–7.3, 8.7, 8.8, 8.10); however, most observed speci- mens have a thecal length between 15 and 20mm. Generally, radial plates have a relatively conical shape with
a blunt summit, usually more accentuated for the third radial plate (e.g., Figs. 2, 5.9–5.11, 7.3, 7.5–7.8, 7.10–7.16, 8.1–8.6, 8.9, 8.10). The radial plates relief can be more or less pronounced; in some specimens, the radials are simply convex (e.g., Figs. 7.1, 7.2, 7.9, 8.7, 8.8). In most specimens, the external surface of thecal plates is entirely smooth. However, in a few individuals, almost all thecal plates show a central, nipple- shaped umbo (e.g., Figs. 5.14, 7.3, 7.4, 8.9, 8.10; already observed by Chauvel, 1971, pl. 2, fig. 4). The stem of R. destombesi is composed of cylindrical
columnals becoming thinner distally (see Ubaghs, 1963, text- fig. 1). The proximal part of the stemis composed of an alternation
of very short and longer columnals (e.g., Figs. 2.4, 2.5, 7.15, 7.16, 8.6, 8.10); this difference disappears progressively distally, as the diameter of the stem decreases. The newly collected material did not yield any specimen showing the distal extremity of the stem. The proximal part is often preserved in connection with the theca, but the distal part of the stem is alwaysmissing.Only a few isolated distal fragments could be observed. As mentioned by Ubaghs (1963), the best-preserved stems of R. destombesi (Fig. 2.4) do not show any evidence of the attachment structure at their distal tip. The brachioles are rarely preserved (Figs. 2.4, 7.2, 7.4, 8.8,
8.9). As indicated by Ubaghs (1963), they are biserial and swollen in their proximal part. Particularly well-preserved and long brachioles can be observed in specimen 1750a (Figs. 7.4, 8.9; not figured by Ubaghs): although their distal tip is missing, they were certainly twice as long as the theca. The morphology of the oral surface—the ambulacra, the
peristomial area, the periproct (posterior interradial area), and the respiratory structures (epispires)—was perfectly described by Ubaghs (1963) and is not further elaborated here (see Ubaghs, 1963, text-figs. 1–8).
Materials.—Seven latex casts of original samples described by Ubaghs (1963): the holotype A 29120 and A 29134 (part and
699
counterpart), A 22122, A 29116, A29122, A 29124, A 29132, A (locality 809 = 1157 = 1725; Fig. 1), and 1750a, b (locality 1737 = 1738 = 1750; Fig. 1). Several latex casts realized of original specimens of Chauvel (1971, 1978) and Chauvel and Régnault (1986): 1157a, b1, c, e–g, i–l, o, p, p', q, and M1725a' (locality 809 = 1157 = 1725; Fig. 1); and 2367a1–a4, b1, e, f (f1, f2), g–i (locality 2367; Fig. 1). Original samples from locality 2367 (Fig. 1): 2367a, b, f, h, i and 2367 SR1, 4–7. One sample from locality Z-F12c (Fig. 1): AA-TISa-OI-9. Eleven samples with numerous external molds of thecae coming from Z-F25 (Fig. 1): ML 20.269.379–382, and UCBL-FSL 711.159– 163, UCBL-FSL 711.650.
Remarks.—Numerous specimens possess supplementary plates (secondary plates, isolated or forming complete circlets) in addition to the seven primary circlets described by Ubaghs (1963). The presence of these additional secondary elements is not a simple by-product of allometric growth: many specimens having a small size possess additional plates (up to two circlets; e.g., Figs. 7.13, 8.4), while other specimens having a larger size have no additional plates, or only isolated ones (e.g., Fig. 7.1– 7.3). For these large individuals, the primary circlets of plates are joined and comprise elements whose size is proportionally large, illustrating a holoperipheric growth mode. This suggests that the theca of R. destombesi could grow in two ways: a simple holoperipheric growth of the plates forming the seven primary circlets of the theca and by inserting new plates (additional secondary plates) between some of these main circlets. Consequently, the diagnosis of R. destombesi (unchanged
since Ubaghs, 1963) was emended to underscore the main characteristics of the species and to consider its morphological variability partly caused by the potential presence of additional secondary plates. Chauvel and Régnault (1986, text-fig. 3A–E) identified
some specimens of R. destombesi showing additional secondary plates inserted between laterals and infralaterals, and between laterals and radials (as isolated plates or forming incomplete circlets). Only one of them could be examined (1157b1, Fig. 7.11). It shows a small secondary plate between the infralaterals and laterals, and its morphology fits well with the
species R. destombesi. The other specimens 1157m, n, and o/1 figured by Chauvel and Régnault (1986, text-fig. 3A, C–E) could not be reexamined, but according to the description and drawings of the authors, the morphological features of these individuals seem to support their assignment to R. destombesi. Ubaghs (1963, text-fig. 9) described a specimen of
R. destombesi that he considered as abnormal due to the presence of additional plates intercalated between infralaterals and laterals, and between the laterals and the first radial circlet. Chauvel and Régnault (1986, text-fig. 3G) identified this
Figure 7. Rhopalocystis destombesi, drawings realized under a stereomicroscope with a camera lucida. (1) 1157q1; (2) 2367h; (3) 1157e1; (4) 1750a1; (5) 2367b1; (6) holotype (A29134 and A29120, part and counterpart), drawing modified from Ubaghs (1963, text-fig. 2.2); (7) ML 20.269.380a; (8) 2367f1; (9) AA- TISa-OI-9a; (10) oral surface of the theca showing the conical radials, the five ambulacra, the brachioliferous plates, the peristomial area, and the anal region containing the periproct, (holotype A29134 and A29120, part and counterpart), drawing modified from Ubaghs (1963, text-fig. 2.3); (11) 1157b1; (12) 2367 SR5; (13) 2367a1; (14) 2367 SR1; (15) 2367 SR6; (16) 2367a3. (1, 11–16) Specimens showing seven primary circlets of plates and additional secondary plates, as isolated plates or forming one complete or incomplete circlet, which can be inserted between infralaterals and laterals, and between laterals and radials; (2–9) specimens possessing only the seven primary circlets of plates that characterize the species, without additional secondary plates. (1, 3, 6, 10, 11) Locality 809 (=1157 = 1725), late Tremadocian (A. murrayi Zone); (2, 5, 8, 12–16) locality 2367, late Tremadocian (H. copiosus Zone); (4) locality 1750 (=1737 = 1738), late Tremadocian (A. murrayi Zone); (7) locality Z-F25, middle Floian (?B. jacksoni Zone); (9) locality Z-F12c, late Tremadocian (A. murrayi Zone). p. = periproct; an. p. = anal protuberance; br. = brachioliferous plates; o. = oral plates. (1–9, 11–16) Scale bar = 1 cm; (10) scale bar = 5mm.
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