Stoloharpes calceolus, Johnson, 2024

Johnson, Robert G., 2024, Devonian Harpetidae from the central and eastern Anti-Atlas, Morocco, Zootaxa 5450 (1), pp. 1-185 : 97-98

Stoloharpes calceolus n. sp.

Plate 49G–K

Diagnosis. Cephalon mildly pyriform; glabella sloping gently anteriorly and narrow, width (tr.) just over 50% of length (sag.) of glabella anterior to S0. Axial furrows nearly straight and weakly converging anteriorly. Preaxial furrows also converging and initially deep, becoming shallower anteriorly as anterior boss deflates to disappear close to girder. Occipital ring with prominent occipital node. Alar furrow well-defined and eyes elongated (exsag.). Genal roll sloping anteriorly at same angle as anterior of glabella, just under 250. Laterally, slope steepens strongly to around 550. Brim strongly convex, moderately broad (sag.) and steeply sloping at around 350.

Etymology. Named after the species’ slipper-like lateral profile.

Material and occurrence. Holotype: NHMUK It 29363, Pl. 49G–K , from “ Basseiarges Couche ”, Eifelian, Ksar Lbor ( Fig.2B, Map 3, site 3), dorsal exoskeleton with pygidium enrolled.

Other material: S. aff. calceolus, NHMUK It 299381, Pl. 49L–P , from “ Basseiarges Couche ”, Eifelian, Ksar Lbor, 28 km E of Tinghir, at the base of Jbel Tisdafine ( Fig. 2B, Map 3, site 4), dorsal exoskeleton of cephalon and partial thorax only.

Description. Cephalon weakly pyriform, narrow, length (sag.) 85% of width (tr.) and widest at mid-point between eye lobes and alae. Genicranium very narrow, width (tr.) being same as length (sag.), widest at posterior border. Glabella strongly carinate, sloping very gently anteriorly and narrow, width (tr.) at S1 being about half sagittal length of glabella anterior to S0. S1 rises obliquely from axial furrow, before fading halfway up glabella. Other lateral glabellar impressions are missing and L1 inflated. Axial furrows straight and converging weakly anteriorly. Occipital ring slightly broadened medially and with prominent occipital node, base of which reaches down into occipital furrow. Top of occipital node only just lower than crest of glabella anterior to S0. Alae nearly as broad (tr.) as long (exsag.), anterolaterally directed and not quite reaching halfway across genal area. Alar furrows are well-defined. Posterior border short (tr.), around 35% of occipital ring width (tr.).

Eye lobes large (exsag.), and no eye ridge. Anterior boss narrow, inflated, strongly connected to glabella but not reaching down to girder. Preaxial furrows slightly convergent anteriorly. Genal roll wide and sloping very gently at just under 250 anteriorly, steepening to about 550 posterolaterally. In lateral view, inner fringe narrows strongly posterolaterally. Fine perforations, relatively sparsely distributed, increase in size on extensions to genal roll on prolongations. Girder narrow and lacking girder kink.

Brim convex in profile, steeply-sloping at around 340 and moderately broad (sag.), being just over 30% of cephalic length (sag.). Brim width ratio 0.70. Brim crossed by light caeca, with a high density of perforations in spaces in between (34 per sq. mm). Diameter of standardised brim perforations averaging just under 95 μm.

Length of prolongations (exsag.) 88% of cephalic length (sag.). External rim narrow, dorsal surface convex. In dorsal view, external rim flares almost imperceptibly outwards as it crosses onto prolongation and then, slanting gently adaxially, continues in a straight line posteriorly for about two-thirds of length (exsag.) of prolongation, where it curves adaxially.

The internal rim, leaving posterior border slanting abaxially at an angle of around 400 to axis, curves steadily adaxially until it meets external rim, where it is again at an angle of around 400 to axis. In lateral view, external rim curves up distally to meet internal rim at an angle of around 600. Internal rim straight in profile, slopes downwards gently from posterior border. Girder, on crossing onto prolongation, slopes sharply upwards, before curving posteriorly to join internal rim about one fifth of its way down prolongation (exsag.). Tubercles on dorsal surface of internal rim. Brim on prolongations quickly steepens posteriorly, to an angle to horizontal of around 80°. Perforations and caeca on brim of prolongations are same as on rest of brim, except for line of slightly bigger perforations which runs just below internal rim. Genal spine short and slanting adaxially.

Thorax has at least 24 segments. Interpleural furrows moderately deep. Distally, pleurae turn down and curve sharply forward, terminating with rounded end ( Pl. 49K ). Pygidium enrolled and hidden.

Hypostome not known.

Remarks. Stoloharpes calceolus is similar to S. aff. capricornus but differs in having: a cephalon that is not so strongly pyriform, and widest at the mid-point between the eye lobes and the alae not at the eye lobes; the genicranium widest at the eye lobes and not at the mid-point between the eye lobes and the alae; the flanks of the glabella more tectiform than rounded; the muscle insertion furrow at S1 slanting posteriorly, reaching two thirds of the way up the flank of the glabella, whereas the S1 furrow on S. aff. capricornus is effaced; an anterior boss and light caeca reaching across brim, while the anterior boss of S. aff. capricornus is effaced and the brim lacks caeca; prolongations that are about 10% shorter in relation to cephalic length (sag.) than those of S. aff. calceolus ; and shorter genal spines that are set at an oblique angle to the exterior rim rather than following its curve.

Other material, NHMUK It 299381 ( Pl. 49L–P ), is designated as S. aff. calceolus differs from S. calceolus by having: the widest point of the cephalon at the level of the eyes rather than halfway between the eye lobes and alae; a wider glabella and a L1 that is not inflated; a shallower and wider (sag.) occipital furrow that is medially straight; alae that are laterally rather than anterolaterally directed; a poorly defined eye ridge rather than none; preaxial furrows that do not converge anteriorly; an anterior boss that is less inflated and not joined to the glabella; a higher brim width ratio and a marginal band that is near vertical rather than sloping down under the cephalon.

The holotype of M. calceolus is well preserved complete cephalon and thorax of a size that would indicate that they belonged to a well-developed holaspid. The cephalon is symmetrical and without any apparent pathological defects and has significant differences with S. aff. calceolus , the species it is most similar too. On this basis the species has been erected although without the support of paratypes.

Figures

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.