Harpes boudibensis, Johnson, 2024

Johnson, Robert G., 2024, Devonian Harpetidae from the central and eastern Anti-Atlas, Morocco, Zootaxa 5450 (1), pp. 1-185 : 44-46

Harpes boudibensis n. sp.

Plate 1A–Q

Diagnosis. Narrow cephalon, width (tr.) around 1.2 times sagittal length and widest (tr.) just posterior to eyes. Glabella cone-shaped, anteriorly rounded. Extension of axial furrow across ala distinct. Alae inflated and alar furrows proximally deep, becoming very shallow distally. Alar depression pronounced. Prolongations around same length (exsag.) as cephalon (sag.). In lateral view external rim posteriorly curving upwards and internal rim wave-like in shape and terminated by short genal spine. Over 25 thoracic segments.

Etymology. Named after the village bou Dîb, which is close to the type locality.

Material and occurrence. Holotype: NHMUK It 29227, Pl. 1K–Q , from horizon 1, Section 2 ( Fig. 7 ), El Otfal Formation, Eifelian, Jbel Issoumour ( Fig. 2B, Map 7, site 4), enrolled articulated dorsal exoskeleton . Paratypes: NHMUK It 29226, Pl. 1A–D , articulated dorsal exoskeleton and NHMUK It 29228, Pl. 1E–J , dorsal exoskeleton, pygidium enrolled. NHMUK It 29226 and NHMUK It 29228 from the type locality and horizon, site 1 and site 5, respectively. Harpes boudibensis is almost certainly present at other Jbel Issoumour Eifelian localities, many of which have been extensively mined for harpetid trilobites.

Other material: cf. boudibensis, NHMUK It 29225 from horizon 7, Section 1 ( Fig. 6 ), El Otfal Formation, Jbel Ou-Driss ( Fig. 2B, Map 4, site 11), Pl. 2A–D , an enrolled dorsal exoskeleton. Horizon 7 of a similar age to the H. boudibensis horizons on Jebel Issoumour

Description. In dorsal view, cephalon widest just posterior to level of eyes, where length (sag.) ≈ 80% of width (tr.). Cephalon and glabella strongly vaulted. Glabella cone-shaped, rounded anteriorly and sometimes with sparse fine tubercles along posterior two thirds of top of glabella. L1 weakly inflated. S1, S2 and S3 poorly marked by change in tone of cuticle ( Pl. 1P ). Shallow furrow which rises 2/3 of way up flank of glabella delineates posterior edge of S1 muscle attachment scar area ( Pl. 1A ). S1 tulip-shaped, S2 and S3 subcircular and about 1/4 size of S1. S0 oval and about two thirds of area of S1. S1 with subparallel intermittent dark vertical stripes and dark edge.

Preglabellar furrow very shallow and preglabellar genal area length (sag.) around 45% of width (tr.) of glabella at S1. Axial furrows deepening posteriorly and alar depression prominent. Alae large, reaching more than 70% of way across (tr.) genal area. Low rounded ridge crosses (exsag.) ala close to axial furrow, visible on holotype in Pl. 1M (lateral view) and in dorsal view on paratype NHMUK It 29226 ( Pl. 1A ). Alar furrows shallow, well-defined, becoming shallow distally. Occipital furrow broad, occipital ring narrow (sag. and exsag.) and covered with fine granular tubercles. Larger , low axial tubercle located on anterior edge of ring. Posterior border very short (tr.), ≈30% of width (tr.) of occipital ring. Genal area narrow, width (tr.) around 50% of length (exsag.). Eye lobes nearly conical in shape, reaching across to near inner margin of fringe, with eye position ratio about 0.85. Two horizontal oval eye lenses stadium-shape and well separated, face outwards anterolaterally and posterolaterally, respectively ( Pls 1Q , 2M ). Broad low ridge reaching down from between the two lenses onto genal area, where it narrows and forms a very faint genal ridge, extending posterolaterally to cross inner margin of fringe level with ala. Genal roll convex, wide and sloping gently anteriorly at under 400 and laterally more steeply at around 550 .

Brim sloping moderately anteriorly; width (sag.) about 30% of cephalic length (sag.) and brim width ratio around 0.50. A row of large perforations lie either side of girder, away from which perforations quickly decrease in size to those on main part of genal roll and brim respectively. Average standardised diameter of perforations on central part of brim around 150 μm ( Pl. 1D, J, O ). Perforations on main part of genal roll finer ( Pl. 1N ) except where inner margin of fringe crosses in front of glabella, where there is a row of larger perforations. Around external margin of brim, usual row of coarser perforations. External rim raised and broad with dorsal rim suture central. Marginal band straight, vertical and without tubercles. Material described includes one poorly preserved hypostome ( Pl. 1H, I ), which has an inverted cone shape with no discernible middle furrow and narrow borders.

Prolongations around 1.05 times sagittal cephalic length and internal rims set at about 1400 to posterior border, curving inwards posteriorly so that distal ends point obliquely adaxially. In lateral view, external brim narrows and curves steadily upwards posteriorly to meet internal rim at end of prolongation. Internal rim rises gently from posterior border then curves down towards distal end, before curving up to meet external rim to form very short stout spine. Lateral profile of internal rim wave-like. In dorsal view, internal rim broad, rounded and covered by small tubercles. Extension of girder on prolongations rises to run just under internal rim before joining it at about midpoint. Perforations on extension of genal roll on prolongation increase in size towards internal rim. Below internal rim a row of large perforations becoming smaller posteriorly.

Thorax has 26 to 28 thoracic segments. Axis strongly vaulted and with axial rings becoming narrower (tr.) posteriorly, last having width (tr.) of about 30% of first. Postannuli wider (sag. and exsag.) than preannuli and not narrowing medially. Pleurae widening (tr.) posteriorly until 7 th segment and then narrowing until last segment which is just over 20% of 7 th. Pleurae narrow (exsag.) with anterior and posterior bands approximately same width (exsag.) and a relatively deep pleural furrow. Pleural furrows cross onto outer portion of pleurae, which are turned downwards, straight and terminate in rounded end. Pygidium very short (sag.) with two axial rings and pleural furrows extending to distal edge. Terminal piece short (sag.) and rounded.

Remarks. Harpes boudibensis differs from H. macrocephalus in having a cephalon which is widest (tr.) just posterior to the eye lobes rather than the anterior of the alae and is ovoid rather than U-shaped. Its glabella anterior to S0 lacks tubercles and S1 furrow is shallower, becoming effaced before reaching the top of muscle attachment area. Preglabellar furrow of H. boudibensis is very shallow as is the extension of the axial furrow across the ala. Genal area and genal roll not so strongly convex and anterior slope of genal roll is under 400 compared with over 500 for that of H. macrocephalus . The prolongations are a third longer (exsag.) in relation to length (sag.) of cephalon than those of H. macrocephalus . In dorsal view, internal rims curve adaxially rather than being subparallel and in lateral view, their profile is wave-like rather than straight.

Harpes cf. boudibensis, NHMUK it 29225, ( Pl. 2A–D ) is very similar to H. boudibensis but differs in having fine tubercles scattered along top of the glabella, a wider occipital furrow which is medially bent forward, an occipital ring which is narrower, a slightly shorter (tr.) posterior border, more inflated alae and a steeper-sloping genal roll (sag.). Some of these features are shared with H. Lahceni .

Harpes boudibensis has been widely mistaken for Helioharpes perradiatus ( Richter & Richter, 1943) in the Moroccan trilobite mining industry, and by Ebach & McNamara (2002) and most likely Beech & Lamsdell (2021). The type locality of Helioharpes perradiatus , Dechra-ait-Abdallah, is some 250 km North-North-West of bou Dîb on the southern edge of the Moroccan Central Meseta. Harpes perradiatus differs from H. boudibensis in having a less vaulted cephalon and less steep genal roll; a less inflated glabella which is subcylindrical rather than oval or cone-shaped and is without tubercles. Eye lobe is small and is not cone-shaped and the brim does not narrow posterolaterally. The brim width of H. boudibensis reduces (tr.) posterolaterally to become one half of its sagittal width at posterior border. Also, there is a strong web-like caeca on the brim, forming pseudo perforations and caeca on genal roll, not present on H. boudibensis .

Figures

PLATE 1. A–Q Harpes boudibensis n. sp., El Otfal Formation, Eifelian. A–D, articulated dorsal exoskeleton, paratype, NHMUK It 29226, type locality horizon 1 (site 1). A, dorsal, B, lateral and C, anterior view. D, dorsal view of brim perforations. E–J, dorsal exoskeleton, pygidium enrolled, paratype, NHMUK It 29228, type locality, horizon 2 (site 5). E, anterior, F, dorsal and G, lateral view. H, ventral view of anterior part of cephalon, I, hypostome and J, dorsal view of brim perforations. K–Q, enrolled articulated dorsal exoskeleton, holotype, NHMUK It 29227, horizon 1, Section 2 (Fig. 7), Jbel Issoumour (Fig. 2B, Map 7, site 4). K, dorsal, L, anterior, M, lateral view, N, anterior dorsal view of genal roll and brim perforations, O, dorsal view of brim perforations, P, lateral dorsal view of eye lobe and muscle impression areas at S0, S1, S2 and S3, and Q, lateral view of eye lobe. Scale bars shown represent 1 cm unless otherwise indicated.

PLATE 2. A–D Harpes cf. boudibensis, from horizon 7, Section 1 (Fig. 6), El Otfal Formation, Eifelian, Jbel Ou-Driss (Fig. 2B, Map 4, site 11). An enrolled dorsal exoskeleton NHMUK It 29225. A, dorsal, B, lateral and C, anterior view. D, dorsal view of brim perforations. E–M Harpes oudris, from horizon 5, Section 1 (Fig. 6), El Otfal Formation, Eifelian, Jbel Ou-Driss (Fig. 2B, Map 4). E–H, enrolled dorsal exoskeleton, paratype, NHMUK It 29240 (site 21). E, dorsal, F, lateral and G, anterior view. H, dorsal view of brim perforations. I–M Harpes oudris, enrolled dorsal exoskeleton, holotype, NHMUK It 29241 (site 22). I, dorsal, J, lateral and K, anterior view. L, dorsal view of brim perforations and M, lateral view of eye lobe. Scale bars shown represent 1 cm unless otherwise indicated.

FIGURE 6. Section 1 Jbel Ou-Driss

FIGURE 7. Section 2 Jbel Issoumour