Harebayaspis plurima, Adrain & Pérez-Peris, 2021

Adrain, Jonathan M. & Pérez-Peris, Francesc, 2021, Middle Ordovician (Darriwilian) cheirurid trilobites from the Table Cove Formation, western Newfoundland, Canada, Zootaxa 5041 (1), pp. 1-73 : 35-37

Harebayaspis plurima n. sp.

Plates 13–16

Material. Holotype, pygidium, GSC 135277 (Pl. 16, figs 8, 9, 13, 17, 18), from horizon TCM 24, and assigned specimens GSC 135256 , 135257 , 135259 , 135260 , 135261 , 135264–135268 , 135274 , 135275 from horizon TCM 24, GSC 135258 , 135262 , 135273 , 135276 , 135279 from horizon TCM 18, GSC 135255 , 135263 , 135269 , 135271 , 135272 , 135278 from locality TCL 2, and GSC 135270 from locality TCL 6.

Etymology. Latin plurimus: most, in reference to the high number of pygidial segments.

Diagnosis. Eye set close to glabella, eye ridge short; fixigena abaxial to palpebral lobe narrow and turned posteriorly; librigenal field with large caecal pits and robustly inflated caecal trunks; pygidium with seven segments.

Description. Cranidial measurements are based on the specimens of Plate 13 , figures 2, 17. Cranidium subtrapezoidal in outline, broad (tr.) with maximum width across genal angles (excluding genal spines), tapering forward, slightly vaulted medially, in anterior view fixigenal field downturned abaxially, in lateral view subtly sloping downwards from the horizontal anteriorly; anterior border describing a broad arch directed forward with the medial portion opposite to the frontal lobe of the glabella almost transverse, medially and in most distal region shorter (sag., exsag.), maximum length (sag.) opposite intersection of S3 with axial furrow (e.g., Pl. 13, figs 2, 3), in anterior view medial part slightly vaulted dorsally (e.g., Pl. 13, fig. 5), gradually flattening distally, with sculpture of densely and evenly distributed tiny granules; anterior border furrow short (sag.), deeply incised, describing an anteriorly directed arch opposite glabella, with the median part almost transverse, distally beyond the glabella running slightly posteriorly, slightly anteriorly convex; glabella subrectangular in outline, with sagittal length 98.85% (96.2–101.5%) maximum glabellar width across L1, lateral margins subparallel, subtly tapering forward, anterolateral corners slightly rounded, posterolateral corners more squared off, anterior margin describing anterior arch with the medial part almost transverse, posterior margin with medial part transverse and distally slightly concave anteriorly across L1, anterior part slightly vaulted, posterior part flatter, sloped downward from the horizontal anterior to S1 (e.g., Pl. 13, fig. 5), with sculpture of dense medium-sized tubercles (larger than on the anterior border) arranged in arcs flanking the glabellar furrows (e.g., Pl. 13, figs 1, 2); S1–S3 well defined, deeply incised, relatively short (exsag.), extending about three quarters of the glabellar width; S1 slightly longer (sag.) than S2/S3, deeply incised distally and shallower proximally, directed posteromedially with the most proximal part curving more posteriorly, not connected with SO, proximal tip followed by a shallow dorsal depression that connects with SO and separates L1 from the median glabellar part; S2 parallel to S1, similar width and depth to S1; S3 shorter than S1/S2, strongly directed backwards; SO deeply incised, slightly shallower medially, long (sag.) behind median glabellar area, shorter abaxially; LO subrectangular in outline, relatively long in medial part behind median glabellar area, slightly shorter laterally, anterior margin transverse, slightly anteriorly concave medially, with distal part running slightly forward, posterior margin describing a broad posteriorly directed arch, corners squared off with the anterior corner slightly more extended outwardly than posterior corner, sculpture similar to that of the glabella; L1 wedge-shaped, slightly longer (exsag.) than L2, posterior margin subtly bowed posteriorly, dorsally inflated compared with the median area of the glabella (e.g., Pl. 13, fig. 11); L2 and L3 subrectangular in outline, similar in size, slightly shorter (exsag.) than L1; frontal lobe subtrapezoidal in outline, broader anteriorly, tapering posteriorly, slightly shorter than L1–L3; axial furrow deep and narrow, similar to the glabellar furrows; fixigenal field subtriangular in outline, with sculpture of dense irregular caecal pits of medium size and small tubercles distributed evenly across the surface; anterior fixigena shorter (exsag.) and narrower (tr.) than posterior part, in anterior view almost transverse to the horizontal, divided by eye ridge into anterior and posterior part (e.g., Pl. 13, figs 1, 2, 3, 10); anterior part very small with same width as the rest of anterior fixigena, very short (sag.), shorter laterally; posterior part of the anterior fixigena triangular in outline, anterior margin anterolaterally concave; posterior part of the fixigena subrectangular in outline, wider than long, anterior margin directed slightly posteriorly, in anterior view proximal part almost transverse to the horizontal and distal part downturned; posterior border furrow narrow deeply incised, short (sag., exsag.), transversely directed adaxial to genal angle, then abruptly curved anteriorly and slightly laterally; lateral border furrow with similar width and depth as the posterior border furrow, directed anterolaterally; posterior border shorter (exsag.) opposite L1, lengthening gradually abaxially until maximum length at genal angle, distally the genal angle is abruptly curved, anterior margin transverse, posterior margin slightly running posteriorly; genal spine conical in shape, directed posterolaterally, tapering distally, ending in a pointed tip (e.g., Pl. 15, figs 12, 13, 15, 16); lateral border short (exsag.) and narrow (tr.), directed anteriorly and slightly laterally, wider near the genal angle, narrowing forward; posterior border, genal spine and lateral border share a sculpture of densely distributed tiny tubercles; palpebral lobe small, posterior end set opposite L2, anterior end continuous with a well defined eye ridge (e.g., Pl. 13, figs 3, 6, 10), eye ridge running adaxially and anteriorly, connected proximally to axial furrow just posterior to the intersection of S3 with axial furrow; palpebral furrow running anteriorly from the posterior end of the palpebral lobe, merged anteriorly with a fine furrow running along the posterior side of the eye ridge; doublure beneath LO short (sag.). approximately half the sagittal length of LO; very short (exsag.), transverse doublure beneath the posterior border, slightly expanded under the genal angle.

Librigenal measurements were made on the specimens of Plate 14 , figures 18, 19, 20. Librigena narrow, elongate; eye small, set in the middle of the librigena, separated from field by smooth, weakly inflated socle lacking sculpture; librigenal field triangular in outline, elongate and narrow, width of field 36.4% (31.6–40.7%) length along lateral border furrow; in lateral view field slopes downward from the base of the eye to border furrow; field with sculpture of small to medium caecal pits and anastomosing caecal trunks, with tiny tubercles scattered irregularly over trunks; border furrow deep, narrow, slightly bowed laterally; border narrow, with width 57.1% (50.0–66.7%) width of field, outer margin gently curved laterally; posterior projection slightly longer than anterior projection, slightly curved medially in external view; anterior projection curved medially; posterior facial suture long curving convexly laterally, changing slope opposite border furrow from slightly curved laterally through the border to adaxially (e.g., Pl. 14, fig. 18); anterior facial suture short, curved laterally, with a gentle slope opposite border furrow; lateral border doublure very narrow beneath the entire border (e.g., Pl. 14, figs 21, 22), lacking sculpture.

Rostral plate, hypostome, and thorax unknown.

Pygidial measurements were made on the specimens of Plate 15 , figure 1, and Plate 16 figure 9. Pygidium approximately semicircular in outline, broader anteriorly across the first pleural segment, narrowing posteriorly, sagittal length (excluding articulating half-ring and pleural spines) 45.5% (40.3–45.5%) maximum width (excluding pleural spines), anterior part slightly vaulted medially; fulcrum set far from the axis (e.g., Pl. 16, fig. 18), pleurae slightly downturned distal to the fulcrum, almost transverse; articulating half-ring short, longer sagittally with sagittal length 10.0% (8.9–11.1%) pygidial length, shorter exsagittally, anterior margin broadly bowed anteriorly, posterior almost transverse, vaulted dorsally, smooth; articulating furrow short (sag., exsag.), longer sagittally, slightly shorter exsagittally, shallow, deepening exsagittally; axis composed of seven axial rings, narrow and elongate, with sagittal length 147.6% (142.3–152.9%) maximum width across first axial ring, slightly tapering posteriorly, slightly vaulted anteriorly, gradually flattening posteriorly (e.g., Pl. 16, fig. 8); axial rings with sculpture of evenly distributed medium-sized tubercles; first six axial rings similar in shape, subrectangular in outline, gradually reducing in length (sag.) and width (tr.) from the first to the sixth segment; each of first six segments slightly shorter sagittally, longer exsagittally, anterior margin slightly bowed posteriorly, posterior margin slightly bowed anteriorly, corners squared off; seventh axial ring semicircular in outline, longer sagittally, much shorter exsagittally, anterior margin transverse, posterior posteriorly bowed; terminal piece absent; six inter-ring furrows, decreasing gradually in length (sag.) and width (tr.) from anterior to posterior, longer sagittally, shorter exsagittally, shallow sagittally, slightly deeper exsagittally; axial furrow with width similar to length of articulating furrow, forming wider areas in the intersections with inter-ring furrows, pleural furrows and interpleural furrows, deeply incised anteriorly, shallowing posteriorly; first pleural segment divided by a short (exsag.) and deep pleural furrow; pleural furrow with transverse course, distal part slightly curved posteriorly (e.g., Pl. 16, fig. 9), anterior pleural band shorter (exsag.) than posterior pleural band, transverse, distal tip slightly curved posteriorly, extended slightly beyond the pygidial margin; posterior pleural band long (sag.), running transversely, curving posteriorly before reaching pygidial margin, slightly longer (exsag.) across the pygidial margin, extended beyond pygidial margin by a pleural spine; pleural spine running posterolaterally, conical in outline, circular in cross-section (e.g., Pl. 16, fig. 17); second to fifth pleural segments with similar morphology, divided in anterior and posterior band by a pleural furrow as the first pleural segment, pleural spines more posteriorly directed in the more posterior segments; sixth and seventh pleural segments with pleural furrow and anterior pleural band obscure, segments strongly directed backwards; pleural segments separated by six interpleural furrows similar in lenght (sag.), width (tr.) and depth to pleural furrows, forming a wider area distally in the intersection with the pleural furrows (e.g., Pl. 16, figs 9, 14); posteriorly, interpleural furrows become gradually narrower (tr.), ending distally in the pygidial margin, first interpleural furrow running almost transversely, curving posteriorly slightly distally, posterior furrows directed more strongly posteriorly, shallowing distally across the pygidial margin; pleural segments with dense sculpture of medium-sized tubercles, similar to axis; pygidial margin forming continuous ventral rim (e.g., Pl. 15, fig. 2, Pl. 16, fig. 13); doublure very short, set vertically above margin (e.g., Pl. 15, fig. 4, pl. 16, fig. 18).

Discussion. Harebayaspis plurima is most similar among known species to H. rafi , particularly in cephalic features. The eyes are similarly close to the glabella, with relatively short eye ridges. The portion of the fixigena abaxial to the palpebral lobe is quite narrow. In both H. jacquelinae and H. pengi the eye is set further abaxially, the eye ridge is longer, and the abaxial portion of the fixigena is much wider in dorsal view (in large part because it is directed more laterally instead of ventrally). Librigenae of H. plurima have almost the same dimensions as those of H. rafi , and both differ from the wider field seen in H. pengi . The librigenae differ in the larger caecal pits developed on the field in H. plurima . The species differ most obviously in the presence of seven pygidial segments in H. plurima versus four in H. rafi . Even here, though, comparison of just the rear four pygidial segments of H. plurima with the entire pygidium of H. rafi reveals substantial similarity, with faint paired axial tubercles and similar spine positions. Though they are broken in many specimens, the spines are apparently relatively longer in H. plurima .

Figures

PLATE 13

PLATE 14

PLATE 15

PLATE 16