Harpes lahceni, Johnson, 2024

Johnson, Robert G., 2024, Devonian Harpetidae from the central and eastern Anti-Atlas, Morocco, Zootaxa 5450 (1), pp. 1-185 : 46-47

Harpes lahceni n. sp.

Plate 5A–N

Diagnosis. Wide cephalon, width (tr.) across alae about 1.4 times length (sag.). Glabella oval and strongly inflated. Brim barely sloping, slightly concave and narrowing moderately strongly posterolaterally. Alae inflated and axial furrows not extending across alae. Alar furrows become shallower distally. Fine pointed tubercles scattered along top of glabella, on dorsal surface of eye lobes and occipital ring and along dorsal surfaces of external and internal rims. Prolongations up to 15% longer (exsag.) than cephalon (sag.). In lateral view, external rim posteriorly curving upwards and internal rim wave-like in shape. Over 25 thoracic segments.

Etymology. For Ait Hssaine Lahcen, a Moroccan trilobite worker who assisted with fieldwork in the Anti-Atlas.

Material. Holotype: NHMUK It 29232, Pl. 5A–J , from horizon 3, Section 2 ( Fig. 7 ), El Otfal Formation, Eifelian, Jbel Issoumour near bou Dîb ( Fig. 2B, Map 7, site 6) . Paratype: NHMUK It 29233, Pl. 5M, N , from “ Phylonix Couche”, El Otfal Formation, Jbel Oufatene ( Fig. 2B, Map 8, site 6) . Paratype: NHMUK It 29234, Pl. 5K, L , El Otfal Formation, Eifelian from “ Harpes Couche ” just above the Acanthopyge horizon, Timerzit ( Fig. 2B, Map 10, site 2). All articulated dorsal exoskeletons with thorax partly enrolled .

Other material: H. cf lahceni, NHMUK It 29235, Pl. 6I–N , from “ Erbenochile Couche ”, Timrhanrhart Formation, Emsian, 24 km S.W. of Foum Zguid ( Fig. 2A, Map 2, site 6). Partial dorsal exoskeleton of an upper lamella.

Description. In dorsal view, ovoid cephalon widest at mid-point between level of eye lobes and alae, where length (sag.) is around 70% of width (tr.). Cephalon and glabella particularly strongly vaulted. Glabella anterior to S0 more oval than cone-shaped, rounded anteriorly and with sparse tubercles along posterior two thirds of crest. S1 sloping posteriorly before curving anteriorly near crest. No furrows or visible scars at S2 and S3. Preglabellar furrow shallow and preglabellar genal area narrow, with length (sag. exsag.) ≈20% of width (tr.). Axial furrows convex, weakly convergent and not crossing junction of ala and L1. Alae are large, inflated, laterally directed and reaching more than 70% of way across (tr.) genal area. Alar furrows shallow distally. No interalar furrows or ridges but alar depressions present. Occipital furrow deep, broad and medially straight. Occipital ring narrow (sag. and exsag.) and occipital node small, set back from anterior edge of occipital ring. Posterior border very short (tr.), around 20% of width (tr.) of occipital ring.

Genal area narrow, width (tr.) around 53% of length (exsag.). Eye lobes nearly conical in shape and nearly reach across genal area to near inner margin of fringe. Scattered fine tubercles on dorsal surfaces. Eye position ratio about 0.89. Two horizontal oval eye lenses face outwards anterolaterally and posterolaterally respectively ( Pl. 5E ). Broad but low ridge from between the two lenses, reaches down onto genal area, where it narrows and forms a very faint genal ridge extending posterolaterally to cross inner margin of fringe level with anterior of ala. Genal roll convex and wide, narrowing moderately posteriorly and steep, sloping anteriorly at over 600 and laterally at over 700. No anterior boss or girder kink.

Brim gently sloping anteriorly at under 100 and with a width (sag.) of about 28% of cephalic length (sag.); brim width ratio around 0.70. Row of large perforations either side of girder. Average diameter of perforations on central part of standardised brim ≈190 μm ( Pl. 5H ). Above girder, perforations quickly decrease in size to that of perforations on main part of genal roll, which are finer than those of brim. At inner margin of fringe, in front of glabella, a row of larger perforations about the same size as those immediately above girder. Row of coarser perforations around external margin of brim. External rim is raised and broad with dorsal rim suture located closer to outside edge than inside edge. Tubercles on dorsal surface of rim densely packed. Marginal band not visible on material presented here.

Internal rim set at about 1500 to posterior border and curving adaxially posteriorly so that distal ends point obliquely adaxially. In lateral view, profile of internal rim strongly wave-like and upturned distally. Dorsal surface of internal rim broad with densely-packed tubercles. Row of perforations immediately under internal rim larger than those on brim below. Extension of girder meeting internal rim about one third of the way down prolongation. External rim turning upwards posteriorly to meet internal rim at end of prolongation. Genal spine short and stout.

The thorax has 23 thoracic segments and tapers posteriorly so that last segment is just under 40% of width (tr.) of fifth segment (widest point). Axis strongly vaulted and with axial rings becoming narrower (tr.) posteriorly, width (tr.) of last being about 40% of the first. Anterior and posterior bands of pleura narrow (exsag.) and of the same width (exsag.). Pleural furrow deep, widening distally and extending onto downturned outer portion of pleura, which has rounded distal end.

Pygidium ( Pl. 5J ) short (sag.) with three axial rings and pleurae and a very short (sag.) terminal piece. Axial rings wide (tr.), first axial ring being over 40% of width (tr.) of anterior of pygidium. Interpleural furrows deep, pleural furrows shallow and pleurae distal ends acute.

Remarks. Harpes lahceni’ s morphology complies with the genus diagnostics with the exception of the brim width ratio, which is 10% above the range proposed in Table 5a.

Harpes lahceni is similar to H. whidbornei ( Whittington 1950a, pl. VII, figs 5–12) in the strong vaulting of the cephalon, the steep slope of the anterior of the genicranium and the inflated glabella. The alae of H. whidbornei are more weakly-defined and lack the inflation of those of H. lahceni . Also, H. whidbornei’ s prolongations are shorter and the internal rims, which in lateral view are nearly straight, descend steeply to meet the external rims at the distal ends. The internal rims of H. lahceni initially arch up from the posterior border before curving down and then, towards the distal ends, curving up again forming a wave-like shape. The poor state of the H. whidbornei material makes comparisons of the anatomy of the two species difficult. The thorax of H. whidbornei is unknown and the pygidium attributed by Whidborne (1889 –1892) to H. whidbornei was considered doubtful by Whittington ( Whittington 1950a).

H. lahceni is also similar to H. lentigo ( Pl. F7A–M ) but it has: a glabella that is inset with much finer tubercles a furrow at S1 curving around the top of the muscle insertion area; a preglabellar furrow that in anterior view is straight rather than being bowed up; a broader occipital furrow; axial furrows that do not cross the alae and alae that are wider, more inflated with no interalar furrows; a narrower genal area with scattered fine tubercles but no caeca or pits; larger eye lobes that are cone shaped rather than oval; an inner margin of the fringe the course of which across the anterior of the genal areas is straight not convex; no anterior boss or girder kink; a genal roll with perforations that are the same size as those on the brim not smaller as in the case of H. lentigo ; a brim that slopes less steeply and has a higher brim width ratio, no caeca and perforations that do not become smaller away from the girder; an external rim that has fine tubercles on its dorsal surface; prolongations that are longer and in lateral view have a strong wave like profile; a thorax that is more tapered, inner portion of pleura in line with outer.

A comparison between H. lahceni and its sister species, H. prescheri , is given in the systematics for H. prescheri , below.

Harpes cf. lahceni ( Pl. F6I–N ) differs from H. lahceni in having a brim that is significantly wider at S0 and standardised brim perforations that are over 40% larger. The axial furrow is expressed at L1, the alae are less inflated and there are interalar furrows and ridges not present on the alae of H. lahceni .

Figures

PLATE 5. A–J Harpes lahceni, dorsal exoskeleton partially enrolled, holotype, NHMUK It 29232, from El Otfal Formation, Eifelian, Horizon 3, Section 2 (Fig. 7), Jbel Issoumour (Fig. 2B, Map 7, site 15). A, dorsal, B, lateraland C, anterior view. D, posterior view, showing dorsal surface partially enrolled thorax and pygidium, and ventral surface of prolongations, E, lateral view of eye lobe, F, ventral view of prolongations, G, dorsal lateral view of eye lobe, H, dorsal view of brim perforations, I, dorsal view of dorsal surface of rim and J, dorsal view of pygidium. K–L Harpes lahceni, dorsal exoskeleton partially enrolled, paratype, NHMUK It 29234, from El Otfal Formation, Eifelian, “Harpes Couche” above Acanthopyge horizon, Timerzit (Fig. 2B, Map 10). K, dorsal view and L, lateral view. M–N Harpes lahceni, dorsal exoskeleton partially enrolled, paratype, NHMUK It 29233, from El Otfal Formation, “Phylonix Couche”, Jbel Oufatene (Fig. 2B, Map 8). M, dorsal and N, lateral view. Scale bars shown represent 1 cm unless otherwise indicated.

PLATE 6. A–H Harpes cf. oudris, dorsal exoskeleton with ventral surfaces exposed on anterior half of cephalon, NHMUK It 29242; from El Otfal Formation, Eifelian, horizon 4, Section 1 (Fig. 6), Jbel Ou-Driss (Fig. 2B, Map 4, site 10). A, dorsal, B, anterior and C, lateral view. D, lateral view of glabella (uncoated) and muscle insertion scars, E, ventral view of anterior half of cephalon, F, ventral view of hypostome in place, G, ventral view of anterior of rim, H, dorsal view of brim perforations. I–N Harpes cf. lahceni, dorsal exoskeleton of partial cephalon only, NHMUK It 29235, from “Erbenochile Couche”, Timrhanrhart Formation, Emsian, 23.8 km SW of Foum Zguid (Fig. 2A, Map 2, site 6). I, dorsal, J, anterior and K, lateral view. L, dorsal view of brim perforations and M and N, dorsal and lateral view of eye lobe respectively. Scale bars shown represent 1 cm unless otherwise indicated.

FIGURE 7. Section 2 Jbel Issoumour

PLATE 7. A–M Harpes lentigo n. sp., from a coral horizon 5 m (12.2 m down slope) below the “Morocconites Couche”, Tazoulait Formation, Emsian, Jbel Oufatene (Fig. 2B, Map 8, site 4). A–G dorsal exoskeleton, thorax disarticulated and partially rolled, holotype, NHMUK It 29236.A, dorsal, B, anterior, C, posterior and D, lateral view. E, lateral view of eye lobe (uncoated), F, laterodorsal view of eye lobe (uncoated) and G, dorsal view of brim perforations. H–M Harpes lentigo n. sp., plate of three disarticulated dorsal exoskeletons, paratypes, NHMUK It 29237 (1 to 3) (Fig. 2B, Map 8, site 5). H, dorsal, I, anterodorsal and J, lateral view. K, dorsal view of brim perforations, L, lateral view of pleurae and M, anterior view of rim. Scale bars shown represent 1 cm unless otherwise indicated.