Stoloharpes rissaniensis, Johnson, 2024

Johnson, Robert G., 2024, Devonian Harpetidae from the central and eastern Anti-Atlas, Morocco, Zootaxa 5450 (1), pp. 1-185 : 95-97

Stoloharpes rissaniensis n. sp.

Plates 46A–O , 47A–J , 48A–M

Diagnosis. Cephalon mildly pyriform, genal area narrow (width (tr.) 34% of length (exsag.)). Alae are as wide (tr.) as they are long (exsag.). Genal area narrow. Inner margin of fringe across anterior of genal area straight, and anterior boss barely reaching down to girder. Caeca present on genal roll. Brim sloping at 300, narrow (sag.) (27% of cephalic length (sag.) in dorsal view) and has brim width ratio of just over 0.75. Perforations on brim become smaller for short distance away from girder. Exterior rim curves sharply upwards at posterior of prolongation, to join with internal rim at near right angle. Genal spine short, slanting obliquely upwards and adaxially.

Etymology. Named after the town of Rissani, which is close to the type locality.

Material and occurrence. Holotype: NHMUK It 29373, Pl. 46A–M , from an upper Eifelian horizon, Bou Tchrafine Group (lower corniche), Ksar Gaouz, 9.5 km S.W. of Rissani ( Fig. 2B, Map 14, site 4), dorsal exoskeleton partially enrolled . Paratype: NHMUK It 29376, Pl. 46N–O , from type locality and type horizon ( Fig. 2B, Map 14, site 7), partly crushed dorsal exoskeleton with pygidium enrolled . Paratype: NHMUK It 29374, Pl. 47A–F , from type locality and type horizon ( Fig. 2B, Map 14, site 5), dorsal exoskeleton of cephalon only . Paratype: NHMUK It 29375, Pl. 47G–J , from type locality and type horizon ( Fig. 2B, Map 14, site 6), dorsal exoskeleton of incomplete cephalon with disarticulated thorax . Paratypes: NHMUK It 29371 and NHMUK It 29372, from “ Basseiarges Couche ”, Eifelian, Fezna ( Fig. 2B, Map 6, site 3 and 22, respectively). NHMUK It 29371, Pl. 48A–D , is a dorsal exoskeleton of cephalon only, and NHMUK It 29372, Pl. 48E–J, a cephalon and disarticulated thorax. Paratype: NHMUK It 29377, Pl. 48K–M , from Ighas, Bou Tchrafine Group (lower corniche), Eifelian ( Fig. 2B, Map 14, site 8), dorsal exoskeleton of cephalon only .

Other material: Stoloharpes aff. rissaniensis, NHMUK It 29380, Pl. 49A–F , from an outcrop 3.8 km west of Ksar Hannabou and 8.3 km S.S.W. of El Jorf, Eifelian ( Fig. 2B, Map 6, site 14), a dorsal exoskeleton of a cephalon and partial thorax.

Description. Cephalon weakly pyriform, widest posterior to eye lobes. Genicranium very narrow (width (tr.)> 85% of length (sag.)). Glabella narrow (width (tr.) at S1 just over 60% of glabella length (sag.) anterior to S0); with tectiform flanks; no pitting and S1 sloping posteriorly, but not curving forward over top of muscle attachment area. Muscle attachment areas at S2, S3 and S4 discernible from dark patches in cuticle ( Pls 46L, M , 47E ). L1 is barely inflated, and axial furrows converge weakly anteriorly, at just over 100 to axis. Occipital furrow deep and in dorsal view, moderately bowed posteriorly. Occipital node strongly inflated and occipital ring without sculpture. Alae laterally directed, small (tr.) and as wide (tr.) as it is long (exsag.). Alar furrow very shallow. Posterior border moderately short (tr.), at around 21% width (tr.) of occipital ring.

Genal area narrow, width (tr.) 34% of length (exsag.). Eye lobes oval, large (exsag.), inflated and with two equal-sized lenses each ( Pls 46M , 47F ). Eye ridge straight, poorly defined. Anterior boss barely inflated, reaching down to moderately narrow girder with weak girder kink. Genal roll sloping on sagittal line at an angle of around 310 and laterally at around 550; narrowing posteriorly in lateral view by around 65%. Caeca on genal roll and perforations smaller than on brim. No row of larger perforations immediately above girder. Hypostome unknown.

Brim convex, sloping moderately steeply at just over 310 and narrow, brim width (sag.) of holotype is 27% of cephalic length (sag.). Brim width ratio 0.86. Brim with light caeca and perforations that decrease in size away from girder, to become very fine at under 100µm. No tubercles or granulation on dorsal surface of rim. Marginal band straight, sloping down under cephalon anteriorly and laterally, and lacking tubercles or ridges. Brim steepens quickly to near-vertical on prolongations.

Prolongations moderately long (exsag.), being 87% of cephalic length (sag.), and wide in lateral view, tapering moderately posteriorly. Height of prolongation at midpoint is 65% of height at junction with posterior border. Internal rim straight, gently sloping downwards posteriorly, and external rim straight over 2/3 of its length, before curving strongly upwards to meet internal rim at near right angle. In dorsal view, both rims on prolongations curve adaxially. Genal spine short, continuing curve of external rim. Internal rim lacks tubercles on dorsal surface and extension of girder meets internal rim 1/4 of way down prolongation.

Thorax with 24 segments, not widening anteriorly and not strongly tapered posteriorly. Axis width (tr.) of last segment about 48% of width (tr.) of first. Pleural furrows broad, shallow, U-shaped and well-defined. No pits or tubercles on axial rings or pleurae. Outer portion of pleurae curved anteriorly, tapered and with distal ends rounded. Pygidium short, with 3 axial rings and two pairs of pleural ribs. Terminal piece short (sag.) and subtriangular.

Remarks. The brim of the paratype shown in Pl. 47 A-J is different from that of the holotype, being 20% wider, 10% less steeply-sloping and with a brim width ratio of 0.65 (25% lower than that of the holotype). While some of the difference in width and slope could be explained by flattening of the dorsal exoskeleton of the paratype, difference in brim width ratio cannot and is an example of significant intraspecies variation.

The Anti-Atlas harpetid that S. rissaniensis resembles the most is S. calceolus . S. rissaniensis differs, however, in having: a cephalon that is widest at the eye lobes rather than at the midpoint between the eye lobes and the alae; wider (tr.) alae which are laterally directed not anterolaterally directed; an eye ridge, which is absent in S. calceolus ; a genal roll that slopes anteriorly at around 320 rather than 250; a less inflated anterior boss that reaches down to the girder, which has a weak girder kink; preaxial furrows which do not converge as those of S. calceolus do; a narrower brim; a higher brim width ratio; and brim perforations which become smaller towards the centre of the brim. The differences in brim width (sag.) and brim width ratios are much less in the case of the S. rissaniensis paratypes that have brims wider than those of the holotype.

NHMUK It 29380 ( Pl. 49 A-F) has been designated as Stoloharpes aff. rissaniensis and differs from S. rissaniensis in having: a cephalon that is widest at mid-point between eye lobes and alae, rather than at the eye lobes: a glabella with flanks that are rounded rather than tectiform; a shallow occipital furrow that is not bowed posteriorly medially; L1 that is not inflated; alar furrows that are effaced whereas S. rissaniensis has alar furrows, albeit very shallow; eye lobes with three lenses each, the anterior lens being the largest and the middle lens the smallest and orientated upwards, while S. rissaniensis has two lenses with the anterior being the largest; no eye ridge; no caeca on the genal roll or the brim; brim perforations which do not become smaller towards the centre and which have a standardised diameter of over 200µm, more than twice the diameter of those of S. rissaniensis ; an internal rim that has a shallow wave-like profile in lateral view, whereas that of S. rissaniensis is concave; long genal spines, which follow the curve of the exterior rims; an extension to the girder which meets the internal rim a third of the way down the prolongation; and a brim that does not steepen so strongly on prolongations. Stoloharpes rissaniensis has genal spines that are smaller and set at an oblique angle to the exterior rim and an extension to the girder that meets the internal rim a quarter of the way down the prolongation.

Figures

PLATE 46. A–O Stoloharpes rissaniensis n. sp., El Otfal formation, South Rissani, Eifelian. A–M articulated dorsal exoskeleton with thorax partly enrolled, holotype, NHMUK It 29373 (Fig. 2B, Map 14, site 4). A, dorsal, B, anterior, C, lateral and D, antero-dorsal view. E, Antero-dorsal view of perforations on genal roll and brim, F, G and H, dorsal view of pleurae thorax and pygidium, respectively. I, lateral view of thorax and J, ventral view of exterior rim. K, dorsal view of brim perforations, L, lateral view and M, anterior view of glabella muscle insertion scars (uncoated). N–O partial dorsal exoskeleton with pygidium enrolled, paratype, NHMUK It 29376 (Fig. 2B, Map 14, site 7). N, dorsal view and O, anterior view. Scale bars shown represent 1 cm unless otherwise indicated.

PLATE 47. A–J Stoloharpes rissaniensis n. sp., El Otfal formation, Eifelian, South Rissani. A–F dorsal exoskeleton of cephalon only, paratype, NHMUK It 29374 (Fig. 2B, Map 14, site 5). A, dorsal, B, anterior, C, lateral view. D, dorsal view of brim perforations. E, lateral view of glabella muscle insertion scars (uncoated) and F, lateral view of eye lobe (uncoated). G–J disarticulated dorsal exoskeleton, paratype, NHMUK It 29375 (Fig. 2B, Map 14, site 6). G, dorsal, H, lateral and I, anterodorsal view. J, dorsal view of brim perforation. Scale bars shown represent 1 cm unless otherwise indicated.

PLATE 48. A–M Stoloharpes rissaniensis n. sp., “Basseiarges Couche”, Fezna, Eifelian. A–D dorsal exoskeleton cephalon only, paratype, NHMUK It 29371 (Fig. 2B, Map 6, site 3). A, dorsal, B, lateral and C, anterior view. D, dorsal view of brim perforations. E–J dorsal exoskeleton cephalon and disarticulated thorax, paratype, NHMUK It 29372 (Fig. 2B, Map 6, site 22). E, dorsal, F, lateral and G, anterior view. H and I, lateral view of eye lobes. J, dorsal view of brim perforations. K–M Ighas El Otfal Formation, Eifelian (Fig. 2B, Map 14, site 8), dorsal exoskeleton of cephalon only, paratype, NHMUK It 29377. K, dorsal, L, anterior and M, lateral view. Scale bars shown represent 1 cm unless otherwise indicated.

PLATE 49. A–F Stoloharpes aff. rissaniensis, El Otfal formation, upper Eifelian, Ksar Hannabou (Fig. 2B, Map 6, site 14), dorsal exoskeleton, thorax disarticulated and pygidium missing, NHMUK It 29380. A, dorsal B, lateral and C, anterior view. D, dorsal and E, lateral view of eye lobe (uncoated). F, dorsal view of brim perforations. G–K Stoloharpes calceolus n. sp., “Akantharges Couche”, Eifelian, Ksar Lbor (Fig. 2B, Map 3, site 4), dorsal exoskeleton pygidium enrolled, holotype, NHMUK It 29363. G, dorsal, H, anterior and I, lateral view. J, dorsal view of brim perforations and K, lateral view of pleurae. L–P Stoloharpes aff. calceolus, “Akantharges Couche”, Eifelian, Ksar Lbor (Fig. 2B, Map 3, site 5), dorsal exoskeleton, thorax disarticulated pygidium enrolled, holotype, NHMUK It 29381. L, dorsal, M, anterior, N, lateral and O, posterior view. P, dorsal view of brim perforations. Scale bars shown represent 1 cm unless otherwise indicated.