Componaster spurius, Glass & Blake & Lefebvre, 2024

Glass, Alexander, Blake, Daniel B. & Lefebvre, Bertrand, 2024, An unusual new ophiuroid (Echinodermata) from the Late Ordovician (early Katian) of Morocco, Comptes Rendus Palevol 23 (25), pp. 401-415 : 404-409

Componaster spurius n. gen., n. sp.

( Figs 1-4)

urn:lsid:zoobank.org:act:D6E0704E-575A-4EA6-9AD3-30C9A1CC450D

MATERIAL EXAMINED. — Holotype. Kingdom of Morocco • 1 specimen; Tizi n’Mourghi ( Cricket’s Pass ); Lower Ktaoua Formation , Upper Ordovician (lower Katian); MHNM.15690.113.3.1-2, oral ( MHNM.15690.113.3.1) and aboral ( MHNM.15690.113.3.2) on separate slabs.

Paratypes. Kingdom of Morocco • 17 specimens; same as for the holotype; AA.TNMa. OS.4, AA.TNMa. OS.5, AA.TNMb. OS.13, AA.TNMb. OS.23, AA.TNMb. OS.28, AA.TNMb. OS.29, MHNM.15690.113.1.1-2, MHNT.PAL.2005.0.138.1.1, MHNT. PAL.2005.0.138.2.1, MHNT.PAL.2005.0.146.1.1-8, MHNT. PAL.2005.0.146.2.1-8, MHNT.PAL.2005.0.155 .

TAXON ASSIGNMENTS UNCERTAIN. — Several specimens that cooccur with C. spurius n. gen., n. sp. are too poorly preserved to allow unequivocal assignment. Some exhibit sufficient morphology to be suggestive of C. spurius n. gen., n. sp. and are listed for completeness. These are AA.TNMb.OS.14, AA.TNMb.OS.18.1, AA.TNMb. OS.18.2, AA.TNMb.OS.20, AA.TNMb.OS.26, AA.TNMb. OS.27, AA.TNMb.OS.30, AA.TNMc.OS.2, ML.20.269412, MHNM.15690.113.2.1-2, and MHNT.PAL.2005.0.163.

ETYMOLOGY. — Latin, spurius , false, spurious, illegitimate, in reference to an ophiuroid with form and an aboral skeleton that are suggestive of those of asteroids.

TYPE LOCALITY AND STRATUM. — Lower Ktaoua Formation, Upper Ordovician (lower Katian), Tizi n’Mourghi (Cricket’s Pass), Kingdom of Morocco .

DIAGNOSIS. — Ophiuroid with proximally paired, otherwise ontogenetically offset axials distally. Proximal axials with transverse ridge located proximally along adradial ridge (i.e., “boot-shaped”), but positioned medially in offset axials (i.e., “T-shaped”). Abactinals closely abutted, polygonal, aligned in more or less regular series across the arms and aboral interbrachial areas of the disk. An irregular aboral circlet encloses a central apical ossicle.

DESCRIPTION (HOLOTYPE MHNM.15690.113.3.1-2) Overall form stellate with concave interbrachial margins that smoothly merge with the arms ( Figs 1A, B; 3A, E). Aboral disk covered by closely abutting or partially overlapping ovate to polygonal ossicles, surfaces bearing densely arranged shallow pits ( Figs 1B; 2A, C, E, F). Apex of disk bearing single polygonal ossicle (yellow in Figures 1C; 2B, D, F), it surrounded by circlet of ossicles of which at least four are distinguishable ( Figs 1C; 2B, D, F). A single row of smaller irregular to polygonal, slightly longer than wide ossicles extend across axis of the proximal arm portions (pink in Figures 1C; 2). Where each of these rows enters the disk area it joins a series of similar ossicles (green in Figures 1C; 2B, D, F) that extend parallel to interbrachial margin curvature to join central ossicular rows of neighboring arms. The latter (green in Figure 1C) series of ossicles abut directly to the circlet of ossicles that surround the apex ( Figs 1C; 2D, F). Adjacent, on each side of the mid-arm ossicles extends an additional row of often smaller and slightly longer than wide ossicles (orange in Figures 1C; 2B, D, F, H) that follow the gradual curvature of the interbrachial disk area to the adjacent arm. Evidence of a potential additional outer series of aboral adradial ossicles, as marked by the remnants of multiple individual ossicles of uncertain size and shape along the outermost edges of the disk (see adradial to the orange circlet in Figures 1C). Accessory disk ossicles (spines, granules, articulation sites) not observed. The oral interbrachial disk areas covered by irregular rows of closely abutting, tightly packed, elongated scalar ossicles ( Fig. 3B, C, E). Madreporite not observed.

Arms taper evenly. At least ten axial-adaxial pairs inside disk, free arm length about as or slightly longer than maximum disk diameter ( Figs 1; 2; 3A). Axial arrangement across arm midline inconsistent along and among arms: proximally axials (first 3-4 axials) paired or slightly offset, gradually becoming significantly offset (fully alternating) for remainder of arm ( Figs 1A; 3A, B, E; 4 A-C). Axial midline straight to slightly sinusoidal ( Figs 4A, B). Oral axial adradial ridge surfaces closely abutting proximally and distally, lacking orally visible interaxial muscle gaps ( Figs 3A, E; 4A).Transverse ridge located proximally along the adradial ridge in proximal (first 3-4) axials, thereafter location changes gradually more distally to medially along each axial’s adradial ridge ( Figs 1A; 3A, D, E; 4A). Podial basins round to slightly wider than long ( Figs 1A; 3A, E). Where visible at proximal arm region, podial basin floors formed by the proximal axials, with slightly raised, rounded abradial edges forming rims ( Figs 3D; 4A), some with possible skeletal gaps between basin floor edge and adradial adaxial wall ( Fig. 4A). Aboral surface of axials smooth with proximal and distal boundaries slightly curved abradially and distally, resulting in skewed axial shape ( Fig. 4B, C). Adaxials stout, oral abradial surface slightly below axials. Consecutive adaxials closely abutting proximally and distally. Proximal adaxials with single, distal flange, bordering podial basins. More distally, the abradial podial basin margin is partially shared with a proximal flange on distal adaxial. Abradial edge of adaxials slightly curved ( Figs 3E; 4A). Lateral or groove spines, or associated articulation sites, not recognized. Orally, single adradial podial basin on each mouth angle ossicle, and a proximal-most, scoop-shaped depression between adjacent ( Fig. 3E). Aboral surface of mouth frame ossicles hidden by aboral skeleton.

MORPHOLOGICAL VARIATION IN THE PARATYPES

Some of the paratypes exhibit some minor morphological variation from the holotype. Paratype MHNM.15690.113.1.2 exhibits an additional irregular circlet of ossicles between the centermost (blue in Figure 2B) and the outermost aboral circlet (orange in Figure 2B). This paratype is the largest specimen and presence of additional ossicles could be reflective of increased size. Paratype AA.TNMb.OS.2 ( Fig. 2F) exhibits an unequivocal central apical ossicle surrounded by an aboral circlet of six equally-sized ossicles. In paratype AA.TNMb. OS.28, one of these circlet ossicles appears compound, constructed of three closely fitted ossicles ( Fig. 2D). Paratype AA.TNMb.OS.23 ( Fig. 2H) lacks an unequivocal central apical ossicle and associated circlet but the specimen’s overall poor preservation makes identifying ossicular boundaries particularly difficult.

Paratypes MHNM.15690.113.1.2 ( Fig.2B) and AA.TNMb. OS.28 ( Fig. 2D) support the interpretation of a possible additional series of aboral ossicles along the margin of the disk, as described in the holotype. Alternatively, these features might be the aborally exposed abradial edges of the scalar ossicles that cover the oral interbrachia.

In contrast to the tightly fitted and stout polygonal ossicles on the aboral surface, the interradii of the oral surface consist of oval-shaped scalar ossicles. In places they appear to imbricate slightly towards the mouth as in the holotype ( Fig. 3E). This is also visible in at least one interbrachial of the paratype MHNT.PAL.2005.0.138.2.1 ( Fig. 3B) where they form shingle-like rows, however, they are more irregularly distributed in others ( Fig. 3C), perhaps due to disruption.

The number of proximally paired axials appears to vary within and among specimens.Whereas the holotype exhibits 3-4 paired axials before the first offset, at least one arm in each paratype MHNT.PAL.2005.0.146.1.3 and MHNT. PAL.2005.0.138.2.1 has up to five paired axials. In contrast, paratype MHNT.PAL.2005.0.146.2.3 shows a slight offset of the aboral axial distal surface of the axial immediately beyond the paired circumorals ( Fig. 4C, D), whereas this shift doesn’t occur in some of the arms of paratype MHNT. PAL.2005.0.146.2.8 until the second or third axial after the circumoral ( Fig 4B).

The floors of the podial basins and associated abradial cuplike rims adradial to the abutting adaxial are visible on proximal axials of the holotype and paratype MHNT.PAL.2005.0.146.1.3 ( Fig. 3D). Here, consistent with a proximal abradial ridge, podial basin floors consist of a single axial. Ossicular boundaries of the podial basins shared by consecutive axials due to centrally located adradial ridges are poorly preserved in all available specimens. It cannot be determined unequivocally that shared podial basins consist of a partial distal floor and the proximal floor of the distal axial, as is the case in some other asterozoans, or whether they consist of distally extended floors of the proximal axial.

The aboral surface of the mouth frame is covered by the disk skeleton in the holotype. Paratypes MHNT.PAL.2005.0.146.2.3 and MHNT.PAL.2005.0.146.28 have exposed oral mouth frames that exhibit mouth angle ossicles that are long and slen- der aborally, together with circumorals creating characteristic ophiuran Y-shaped configuration with small, proximal-most torus in MHNT.PAL.2005.0.146.2.3 ( Fig. 4D).

REMARKS ON PRESERVATIONAL AMBIGUITIES

Even though Componaster spurius n. gen., n. sp. is known from multiple specimens in both oral and aboral aspect, ambiguities and poor preservation among and within specimens leave room for alternative interpretations. Some molds are partially filled with a powdery to very-fine, grainy crystalline residue of iron oxide (see Figs 3A, D; 4 B-D). The effects on the latex casts include partial or complete loss of boundaries between ossicles, and a granular surface “veneer” obscuring true ossicular surface textures. Missing or partially preserved ossicles, including variations in ossicular depth, might not necessarily be due to taphonomic or diagenetic factors, but a result of variable infilling of the molds with the iron oxides – affecting the fidelity of the final latex cast. These vagaries challenge observation and interpretation of morphology. In particular, it severely limits the application of the detailed “lateral arm plate” (LAP) morphologies proposed byThuy & Stöhr (2011) and used for post-Paleozoic ophiuroids and Paleozoic crown-group members. Adaxial surfaces in available specimens exhibit too few unambiguous details to allow such a comprehensive analysis.

Among available specimens of C. spurius n. gen., n. sp., the distal-most arm tips have been lost, and ossicular boundaries are equivocal. Whether the mid-arm ossicles, and adjacent aboral series of adradial ossicles extend to the distalmost arm tips cannot be determined.

Coding for Lovén’s law was not possible due to poor preservation and lack of consistent exposure of relevant arm regions.