Allaire et al.—Early Ordovician eocrinoids from Morocco Systematic paleontology


Class Eocrinoidea Jaekel, 1918 Order Ascocystitida Frest, 2005


Family Rhopalocystidae Frest, 2005 Genus Rhopalocystis Ubaghs, 1963


Type species.—Rhopalocystis destombesi Ubaghs, 1963 from the Destombes locality 809 (=1157 = 1725), Zagora area, central Anti-Atlas (Morocco), by original designation.


Other species.—R. fraga Chauvel (1971), R. grandis Chauvel (1971), R. zagoraensis Chauvel (1971), and R. havliceki Chauvel (1978).


Diagnosis.—Claviform theca composed of thick plates bearing circular to elliptical epispires on their margins, pentameral symmetry expressed by the plating of radial circlets, unique and thick basal cup-shaped plate, four pentagonal to hexagonal infralaterals, at least six laterals, five short embedded ambulacra with four to eight plates each bearing long biserial brachioles swollen at their base; lateral periproct on the adoral CD interray, long slowly tapering holomeric stem.


Occurrence.—Middle Tremadocian (A. victoriae Zone) to middle Floian (?B. jacksoni Zone), Fezouata Shale, Agdz- Zagora area, central Anti-Atlas, Morocco.


Remarks.—The original diagnosis of the genus Rhopalocystis (Ubaghs, 1963), was successively modified by Ubaghs (1968) and Sprinkle (1973). It is further emended here to clarify the main characteristics defining the singular morphology of this genus. Fairly good pentameral symmetry is indicated by five perradial areas (each composed of one column of radial plates) and five interradial areas (composed of more numerous plates generally less organized). Several small specimens of eocrinoids (thecal length


5–8mm) coming from locality 2367 were described by Chauvel and Régnault (1986, text-fig. 4). They were interpreted as putative juvenile individuals of either Rhopalocystis or Balantiocystis (Chauvel and Régnault, 1986) or, alternatively, assigned to a new, yet undescribed, genus of small, nail-shaped eocrinoids, possibly related to Ascocystites cuneiformis Chauvel, 1941 (Lefebvre et al., 2016b). Their thecae are composed of four well-organized circlets of plates (one very small basal, four infralaterals, six laterals, and five radials; no interradial plates). The oral surface contains the peristome surrounded by five simple brachioliferous areas (Chauvel and Régnault, 1986). The newmaterial did not yield this type of small specimens, but one of those figured by Chauvel and Régnault (1986, text-fig. 4) was reexamined in this study (specimen M.2367dE). A long and slender stem is preserved articulated to the theca; it ismade up of small cylindrical columnals of different lengths. Numerous well-preserved specimens of Rhopalocystis were collected in the level yielding the small individuals (locality 2367), but no specimens of Balantiocystis were observed. These small specimens could therefore correspond to juvenile indivi- duals of Rhopalocystis sp.


Rhopalocystis destombesi Ubaghs, 1963 Figures 2, 4.1, 4.2, 5.9–5.11, 5.14, 5.17, 7, 8


1963 Rhopalocystis destombesi Ubaghs, p. 27, pl. 1–3, text- figs. 1–9.


1968 Rhopalocystis destombesi; Ubaghs, S481, text-figs. 292, 293, 298, 310.


1971 Rhopalocystis destombesi; Chauvel, p. 46, pl. 2, fig. 4. 1973 Rhopalocystis destombesi; Sprinkle, p. 110. 1986 Rhopalocystis destombesi; Chauvel and Régnault, p. 865, pl. 1, figs. 1–4, text-fig. 3A–E.


1986 Rhopalocystis dehirensis; Chauvel and Régnault, p. 865, pl. 1, figs. 5–8, text-fig. 3F–H.


2007 Rhopalocystis destombesi; Guensburg and Sprinkle, p. 283, text-fig. 3B.


2013 Rhopalocystis destombesi; Kammer et al., p. 4, text-fig. 2A, B, D, E.


2013 Rhopalocystis destombesi; Lefebvre et al., p. 182, text- fig. 14.8b.


2015 Rhopalocystis destombesi; Allaire et al., p. 24, text-fig. 2B–D, F.


2016 Rhopalocystis destombesi; Guensburg et al., p. 263, text- fig. 8A.


2016b Rhopalocystis destombesi;Lefebvreetal.,p.13, text-fig. 8D.


Holotype.—Samples A29134 and A29120 (part and counter- part) from the Fezouata Shale, Zagora area (locality 809; Fig. 1),


Anti-Atlas, Morocco (Ubaghs, 1963, p. 27, pl. 2, figs. 2, 3, pl. 3, fig. 1, text-fig. 1).


Diagnosis.—Rhopalocystis with a theca composed of seven primary circlets of plates, one basal circlet (a single plate), one infralateral circlet (four plates), one lateral circlet (six plates), four radial circlets consisting of five perradial areas (each composed of one column of four radial plates), and five interradial areas composed of plates arranged in four to five successive rows. Infralateral and lateral circlets joined or separated by additional secondary plates (isolated or forming one circlet); some additional


secondary plates can be also present between the lateral and the first radial circlet. Radial plates conical-shaped, with a blunt summit. Thecal plates without ornamentation (smooth surface) or exhibiting a central, nipple-shaped umbo.


Occurrence.—Middle Tremadocian (A. victoriae Zone) to mid- dle Floian (?B. jacksoniZone), Fezouata Shale,Agdz-Zagora area, localities 809 (=1157 = 1725), 1737 (=1738 = 1750), 2367, Z-F12c, and Z-F25 (Fig. 3), central Anti-Atlas (Morocco).


Description.—The theca of R. destombesi consists of seven primary circlets of well-organized and sutured plates with three aboral circlets of plates (a single basal, four infralaterals, six laterals) surmounted by 10 columns of plates: five meridian areas (consisting of radials and supraradials) and five interradial areas (formed of a higher number of elements; one of these areas contains the periproct). The oral surface, the morphology of the ambulacra and the peristome, the respiratory structures, the brachioles, and the stem were described with great accuracy by Ubaghs (1963, p. 26–37). This well-organized and regular thecal morphology is clearly visible in most specimens


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