Ordovician Petraster Billings, 1858 (Asteroidea: Echinodermata) and early asteroid skeletal differentiation Author Blake, Daniel B. Departement of Earth Sciences and Environmental Change, University of Illinois, 3081 NHB, 1301 West Green Street, 61801 Urbana, IL (United States) dblake@illinois.edu Author Lefebvre, Bertrand Université Claude Bernard Lyon 1, ENSL, CNRS, LGL-TPE, 43 boulevard du 11 Novembre, F- 69622 Villeurbanne (France) bertrand.lefebvre@univ-lyon1.fr text Comptes Rendus Palevol 2024 2024-05-29 23 17 217 239 http://dx.doi.org/10.5852/cr-palevol2024v23a17 journal article 305499 10.5852/cr-palevol2024v23a17 8fc26efa-4ffb-4993-bf58-7fb38916b793 1777-571X 14225117 urn:lsid:zoobank.org:pub:C0E27E25-6719-40FD-A2B8-829B484D6C13 Petraster caidramiensis n. sp. (Figs 2; 3) urn:lsid:zoobank.org:act: 6ECFC7FD-1A25-4E53-A8D6-AC8AE7D760B1 DERIVATION OF NAME . — The species name is based on the El Caid Rami area source of the holotype . TYPE MATERIAL . — Holotype . Morocco • UCBL-FSL 712025 [ao] (Vizcaïno coll.). Arm radius approximately 35 mm , disk radius approximately 11-13 mm ; only limited distortion accompanied sediment compaction. Paratypes . Morocco • Specimens are variously preserved, all incomplete. Specimens known from both surfaces marked “[ao]”, only aboral marked “[a]”, only oral marked “[o]”; assignment of some to species is tentative, these also marked “[?]” UCBL-FSL 711739 [o?], UCBL-FSL 711757 [ao], UCBL-FSL 712077 [o?], and UCBL-FSL 712820 [ao?] ( Reboul coll.); UCBL-FSL 712024 [o], UCBL-FSL 712027 [o], and UCBL-FSL 712028 [a] ( Vizcaïno coll.); UCBL-FSL 712910 [a?], UCBL-FSL 712914 [o?], UCBL-FSL 713032 [o], and UCBL-FSL 713034 [a] ( Auvray coll.) . DIAGNOSIS . — Aboral series of arms proportionately delicate, not tightly and closely abutted; many small accessories intercalated among the larger ossicles. Carinals, adradiallia recognized. Axillary similar in size to adjacent inferomarginals; polygonal, enclosed by marginals. Actinal ossicles few, enlarged. Axials bilateral at transverse ridge. MATERIAL EXAMINED . — Three arms and the disk of the holotype , in aboral view, and one arm and a portion of the disk of the oral surface of the counterpart. Abactinals of the medial portion of the disk are collapsed into the disk. Paratypes are variously preserved, all incomplete. TYPE LOCALITY AND HORIZON . — El Caid Rami area, eastern Anti-Atlas, Morocco ; Lower Ktaoua-Upper Tiouririne formations, early-middle Katian, Late Ordovician. DESCRIPTION Petraster in which arms are moderately elongate, R reaching at least c. 37 mm . Aboral series (i.e., all series aboral of inferomarginals) of arms proportionately delicate, not tightly and closely abutted; many small accessories intercalated among larger. Carinal series in part identified by positioning and alignment, series not demonstrably reaching central disk; carinals approximately equidimensional, ossicular central area enlarged, possibly flanged laterally. Arm adradialia appearing weakly aligned in single series, ossicles similar to, approximately aligned with carinals; carinal and adradial series possibly separated by granulate interareas. Madreporite on aboral disk, bordered laterally by enlarged, crescentic ossicles. Superomarginal series on arms clearly defined, differentiation weakening on disk. Arm superomarginals approximately equidimensional, central area of ossicle enlarged, successive ossicles appearing flanged; superomarginals approximately aligned in transverse series with both adjacent carinal and inferomarginal, the latter weakly exposed in aboral aspect. In oral aspect, inferomarginals of disk rectangular, aligned with and abutting adaxial series; appearing to become more nearly equidimensional, less clearly differentiated from adjacent ossicles on arms; surfaces of disk inferomarginals pustulate, possibly with thin, delicate spinelets, no enlarged spines. Intermarginals perhaps numerous on disk but recognition obscured by weakening of superomarginal definition; intermarginals appearing to reach or nearly reach arm tip. Axillary little enlarged relative to adjacent inferomarginals, polygonal, distal end truncated, proximal margin rounded. Actinal ossicles relatively few, quite large, similar in form to adjacent inferomarginals and axillary. Axials approximately equidimensional, sequential axials abutted laterally, not overlapping, approximately bilateral at transverse ridge; transverse channel not well-defined. MAO robust; circumorals enlarged, dumbbell shaped. Adaxial preservation varied among specimens, appearing approximately equidimensional, thought to lack a prominent nose. FIG . 2. — A1-A7 , Petraster caidramiensis n. sp. ; Lower Ktaoua/Upper Tiouririne formations, Late Ordovician (early–middle Katian); El Caid Rami area, Morocco; latex casts; holotype UCBL-FSL 712025: A1 , aboral view of remnant; A2 , A3 , inclined, aboral views of “NE” and “SE” arms of ( A1 ), arrows identify superomarginals ( A2 ) and carinals ( A3 ), adradialia weakly defined; A4 , oral view; axillary abuts MAO, actinals obscure; A5 , midarm axials, adaxials, inferomarginals; A6 , A7 , aboral views, extraxials small, irregular; circumorals dumbbell-shaped ( A7 , arrows ); B , Petraster caidramiensis ?; Lower Ktaoua Formation, Late Ordovician (early Katian); Tarafin Signit, Morocco; latex cast, UCBL-FSL 712910; madreporite ( arrow ) texture granular, bordered to right by crescentic ossicle; disk ossicles not differentiated. Scale bars: A1, A4, A6, B, 10 mm; A2, A3, A5, A7, 5 mm. REMARK Petraster caidrami is separated from P. crozonensis and P. kinahani by presence of only moderately differentiated enlarged aboral arm ossicles with numerous small intercalated granular accessary ossicles; presence of a single pentameral axillary similar in size to adjacent inferomarginals; presence of abutted, bilateral axials, the transverse ridge “T”-shaped.