Maghroharpes ihmadii, Johnson, 2024

Johnson, Robert G., 2024, Devonian Harpetidae from the central and eastern Anti-Atlas, Morocco, Zootaxa 5450 (1), pp. 1-185 : 73-75

Maghroharpes ihmadii n. sp.

Plates 26A–Q , 27A–D

Diagnosis. Glabella subcylindrical, rounded anteriorly, and S1 curving anteriorly near crest.Alar depression present and ala close to axial furrow is inflated to rise slightly above level of genal area. Eye lobe weakly inflated with four lenses, two very small contiguous central eye lenses ( Pl. 26G ) dorsolaterally orientated. Anterior boss inflated and girder moderately narrow (just over 1.5% of width of genicranium). Brim barely sloping but steepening slightly posteriorly along inside edge on prolongations. Brim width ratio ≈ 0.95. External rim fine (<10% of width sag. of brim). Thorax with 20 segments.

Etymology. Named after the trilobite worker, Ihmadi Hssaine, who found the holotype and paratypes.

Material and occurrence. Holotype: NHMUK It 29301, Pl. 26A–G , from the “ Lanceaspis Couche ” Ihandar Formation, Pragian, Jbel Ou-Driss East ( Fig. 2B, Map 4, site 16), dorsal exoskeleton of cephalon only . Paratype: NHMUK It 29302, Pl. 26 H–Q , from type locality and horizon ( Fig. 2B, Map 4, site 17), partially articulated dorsal exoskeleton with pygidium missing and right prolongation with pathological defect . Paratype: NHMUK It 29303, Pl. 27A–D , from type locality and horizon ( Fig. 2B, map 4, site 18), dorsal exoskeleton of cephalon only .

Other material: Maghroharpes cf. ihmadii : NHMUK It 29304, Pl. 27E–K , from “ Kolihapeltis Couche ” ( Johnson & Fortey 2012, fig. 2, Section 1, horizon 3), Oued el Atchane, Ihandar Formation, Pragian, Jbel Oufatene ( Fig. 2B, Map 8, site 14), dorsal exoskeleton pygidium enrolled. Maghroharpes aff. ihmadii : NHMUK It 29305, Pl. 31A–E , from an upper Pragian Couche below Tizinmarzelaghman, Ihandar Formation, bou Lachrhal ( Fig. 2B, Map 9, site 4), dorsal exoskeleton of a partial cephalon.

Description. Cephalon length (sag.) just over two thirds its width (tr.). Glabella broad anterior to S0, width (tr.) just under 70% of length (sag.)), flanks and crest rounded and finely pitted, and axial furrows tapering slightly anteriorly. L1 inflated, and muscle attachment scars of S1, S2, S3 and S4 appear as dark oval areas rising from axial furrow, and S0 rising from base of occipital ring and spreading across L1 ( Pl. 26O, P ). S0 and S1 tulip-shaped, reaching over 50% and 70% of way up occipital furrow and flank of glabella, respectively. Posterior and top of S1 delineated by very faint hook-like furrow. S2 and S3 oval and about one third size of S1, and S4 only just discernible across junction of axial furrow and preglabellar furrow. No furrows associated with S2, S3 and S4. Occipital furrow broad and occipital ring broadened slightly medially. Occipital node small, well inflated, located towards anterior edge of L0. Occipital ring same height as glabella, and free of tubercles. Alae well defined, small (tr.) (22% of width of glabella at S0) and narrow (length (exsag.) being nearly 1.20 times width (tr.)), parabolic in shape and anterolaterally directed to reach nearly 45% across (tr.) genal areas. Alar furrows deep. Posterior border moderately short (tr.) (≈ 33% of width (tr.) of occipital ring) and without tubercles on dorsal surface.

Dorsal surface of genal area with fine pits but no caeca. Eye lobe located on anterolateral slope of genal area, with eye location ratio being just under 0.90. Eye lobe small (exsag.), subcircular, inflated and with what appears to be four eye lenses ( Pls 26E, F, G , 27H, I ), Two large ovoid lenses latero-anteriorly and latero-posteriorly orientated, respectively, and small subcircular furrow around two small contiguous lenses ( Pl. 26G ). Low transverse eye ridges gently arch into axial furrows and, on well preserved specimens, faint genal ridge that crosses obliquely onto fringe and reaches posteriorly to prolongations ( Pl. 26C ). In dorsal view, inner margin of fringe strongly convex across anterior of genal areas. Anterior boss extends from preglabellar furrow to Σ-shaped girder kink. Girder moderately narrow (sag. and exsag.), just over 1.5% of width of genicranium. Genal roll sloping moderately steeply anteriorly (≈ 530) and steeply laterally (≈ 670). Perforations on genal roll fine with row of bigger perforations above girder and along inner margin of fringe, where it crosses anterior boss. Genal roll lacks caeca. In lateral view, inner fringe narrows only moderately posteriorly.

Brim slightly concave, sloping gently downwards, width (sag.) around 32% of cephalic length (sag.). Brim width ratio ≈ 0.93. At proximal edge of brim row of large perforations separated by light caeca, which stretches down from girder onto brim, to occasionally reach outside edge. Standardised brim perforations, at ≈130µm, are a little larger than those on central part of genal roll and are moderately densely-packed, at around 22 per sq.mm ( Pls 26D, K , 27D ). Row of coarse perforations runs along outside edge of brim. External rim raised and narrow (width (sag.) 9% of brim width (sag.), dorsal surface slightly rounded, with internal dorsal rim suture located at about mid-point on rim. Outside edge of marginal band close to vertical, slightly concave with ridge top and bottom.

Prolongations moderately short (exsag.), at around 78% of cephalic length (sag.). External and internal rims on prolongations curve adaxially. Brim steepens slightly on prolongations, and girder extension meets internal rim about halfway along prolongation. Terminal spine carried on lower lamella, short and slanted slightly adaxially. Perforations on extension of genal roll increase in size posteriorly on prolongations. No tubercles on dorsal surface of internal rim and no row of larger perforations below.

Thorax consists of more than 20 segments, widening (tr.) to 7 th segment. Shortest pleurae (inner portion) under 45% of length (tr.) of longest. Pleural furrows moderately broad and well defined. Outer portion of pleurae straight and not offset to inner portion.

Hypostome and pygidium not known.

Remarks. Maghroharpes ihmadii lacks two of the diagnostic characters of its genus as shown in Table 5b. It has an alar depression and its girder is narrower than those of other Maghroharpes species.

Maghroharpes ihmadii is very similar to M. laatchanensis but differs in having: a genicranium that is about 13% broader; a glabella that is less tapered anteriorly and has a crest that is more rounded than carinate; a shallow muscle insertion furrow at S1 that curves around top of muscle insertion area; a distinct rather than shallow preglabellar furrow; an occipital ring that in lateral view is same height as the glabella anterior to S0, not lower, as is that of M. laatchanensis ; a wider (tr.) ala; an alar depression and axial furrows that cross the junction between the ala and L1; a wider (tr.) but thinner (exsag.) posterior border; a narrow preglabellar field rather than none; a broader genal area free of the light caeca found on the genal area of M. laatchanensis ; less inflated eye lobes with four eye lenses each not two; a better-defined curved eye ridge; a more inflated anterior boss; a genal roll that is more steeply sloping and without caeca; a wider girder; a more steeply-sloping brim with bigger perforations and light caeca just reaching on to it, unlike those of M. laatchanensis that reach right across the brim; a much finer external rim; no tubercles on the dorsal surface of internal rim and on the thorax; pleurae lengthening (tr.) to widen the thorax to 5 th segment and not just lengthening to compensate for the narrowing posteriorly of the axial rings; much broader pleural furrows, pleurae that shorten (tr.) less posteriorly; and outer portions of the pleurae in line with the inner portion, not offset as is the case in M. laatchanensis .

Paratype NHMUK It 29302 ( Pl. 26H–Q ) has a damaged prolongation which, judging from the repair to the external border, may have occurred at an earlier intermoult period .

Maghroharpes cf. ihmadii NHMUK It 29304 ( Pl. 27E–K ) differs from M. ihmadii in having a narrower (tr.) genicranium and glabella, alae that are smaller (tr.), and an S1 furrow that is shallower and does not reach as far up the flank of the glabella. Also, the standardised brim perforations are 20% smaller. Maghroharpes aff. ihmadii NHMUK It 29305 ( Pl. 31A–E ) also differs from M. ihmadii in having a more inflated anterior boss, a narrower (sag.) and more concave brim, and an eye lobe with no third central lens ( Pl. 31D ).

Figures

PLATE 26. A–Q Maghroharpes ihmadii n. sp., Ihandar Formation, Pragian, Jebl Ou-Driss. A–G dorsal exoskeleton of cephalon, holotype, NHMUK It 29301 (Fig. 2B, Map 4, site 16). A, dorsal, B, anterior and C, lateral view. D, dorsal view of brim perforations. Eye lobe in lateral view E and G, and in dorsal view, F. H–Q dorsal exoskeleton with pygidium enrolled, paratype, NHMUK It 29302 (Fig. 2B, Map 4, site 17). H, dorsaI, I, lateral, J, anterior and L, posterior-dorsal view. K and Q, dorsal view of brim perforations and pleurae, respectively, M, anterior dorsal view, O and P, lateral views of muscle insertion scars on glabella. N, lateral view of eye lobe. Scale bars shown represent 1 cm unless otherwise indicated.

PLATE 27. A–D Maghroharpes ihmadii n. sp., dorsal exoskeleton of cephalon and disarticulated thorax, paratype, NHMUK It 29303, from type horizon and locality, Ihandar Formation, Pragian. Jbel Ou-Driss (Fig. 2B, Map 4, site 18). A, dorsal, B, lateral and C, anterior view. D, dorsal view of brim perforations. E–K Maghroharpes cf. ihamadii, dorsal exoskeleton pygidium enrolled, NHMUK It 29304, from “Kolihapeltis Couche”, Ihandar Formation, Pragian, Jbel Oufatene (Fig. 2B, Map 8, site 14). E, dorsal, F, anterior and G, lateral view. H, dorsal and I, lateral view of eye lobe. J and K, dorsal view of brim perforations and pleurae, respectively. L–O Magroharpes hammii, dorsal exoskeleton, thorax and disarticulated pygidium, NHMUK It 29297, from Ihandar Formation, Iminwasief (Fig. 2B, Map 4, site 4). L, dorsaI, M, anterior, N, lateral view. O, dorsal view of brim perforations. Scale bars shown represent 1 cm unless otherwise indicated.

PLATE 31. A–E Maghroharpes aff. ihmadii, dorsal exoskeleton of partial cephalon, NHMUK It 29305, from an upper Pragian horizon, Ihandar Formation, bou Lachrhal (Fig. 2B, Map 9, site 4). A, dorsal, B, lateral and C, anterior view. D, lateral view of eye lobe and E, dorsal view of brim perforations. F–K Maghroharpes cf. forteyi, dorsal exoskeleton of partial cephalon, NHMUK It 29284, from top of the Pragian, Ihandar Formation, Oued el Atchane, Jbel Oufatene (Fig. 2B, Map 8, site 20). F, dorsal, G, anterior and H, lateral view. I, lateral view of eye lobe, J, dorsal view of brim perforations and K, pits on axial node. L–N Maghroharpes cf. zguidensis, dorsal exoskeleton of cephalon, NHMUK It 29328, from MerzâAkhsai Formation?, Pragian, Douar Laayoune, Tata (Fig. 2B, Map 1, site 1). L, dorsal and M, lateral view. N, dorsal view of brim perforations. Scale bars shown represent 1 cm unless otherwise indicated.