Stoloharpes retiarius, Johnson, 2024

Johnson, Robert G., 2024, Devonian Harpetidae from the central and eastern Anti-Atlas, Morocco, Zootaxa 5450 (1), pp. 1-185 : 100-101

Stoloharpes retiarius n. sp.

Plates 51A–L , 52A–L

Diagnosis. Cephalon widest at eye lobes, width (tr.) being over 1.46 times length (sag.). Flanks of glabella convex and axial furrows tapered anteriorly. Occipital furrow narrow and occipital ring not medially broadened. Posterior border short (tr.), equal to 25% of occipital ring width (tr.). Perforations on genal roll becoming smaller posterolaterally and no row of larger perforations at the inner margin of fringe across the anterior boss. Brim width ratio high, at around 0.92. Perforations on brim very large and forming net-like web across the dorsal surface. External rim very fine. In dorsal view, internal rim slanting diagonally abaxially, before curving strongly adaxially. No row of larger perforations under internal rim, and brim steepens only moderately on prolongations.

Etymology. Retiarius, Latin for a Roman net fighter, referring to the net like structure of the brim.

Material and occurrence. Holotype: NHMUK It 29368, Pl. 51A–G , from close to Eifelian/Givetian boundary, Bou Tchrafine Group (lower corniche), Ottara ( Fig. 2B, Map 14, site 2), dorsal exoskeleton of a cephalon only . Paratype: NHMUK It 29369, Pl. 51H–L , from type horizon and type location ( Fig. 2B, Map 14, site 3), dorsal exoskeleton of an incomplete cephalon . Paratype: NHMUK It 29367, Pl. 52A–F , from type horizon and type location ( Fig. 2B, Map 14, site 1), dorsal exoskeleton of an incomplete cephalon . Paratype: NHMUK It 29370, Pl. 52G–L , from type horizon and type location ( Fig. 2B, Map 14, site 11), dorsal exoskeleton of cephalon .

Description. Cephalon ovoid, widest at eyes lobes. Genicranium narrow, width (tr.) 1.24 times length (sag.), widest just anterior to alae. Glabella strongly vaulted, not inset, pitted and with convex flanks. S1 furrow effaced, before curving forward, and L1 inflated.Axial furrows shallow, convex and converging strongly anteriorly. Occipital furrow narrow, medially bowed posteriorly. Occipital ring is broad (sag.) but not medially broadened and occipital node broad, moderately inflated. Posterior border 40% of occipital ring width (tr.).

Genal area broad, width (tr.) 0.56 times length (exsag.), and faint pitting on central to outer regions similar to fine perforations present on fringe. These traces are more apparent on internal mould, exposed where small patch of cuticle is missing on holotype ( Pl. 51F ). Alae are anterolaterally directed and reach about halfway across genal area. Eye lobes with two equal-sized, roughly rectangular-shaped lenses and third smaller sub oval lens high up in between. Eye lenses on holotype not clearly defined and appear to have single small tubercle on surface of each lens. Eye ridges not well defined, inner margin of fringe convex across anterior of genal areas, and not marked by row of bigger perforations across anterior boss. Anterior boss inflated, barely reaching girder. Genal roll gently sloping, anteriorly at 420, laterally at 500 and in lateral view broad (sag.) anteriorly, narrowing by more than 40% posterolaterally. Perforations on genal roll are fine and decrease in size posterolaterally and anteriorly upwards away from girder, for some four rows. Genal roll without caeca, and girder very narrow (sag.), at 1.9% of width (tr.) of genicranium, and without kink.

Brim is steeply-sloping (≈ 270); moderately wide (sag.), being one third of cephalic length (sag.); and has high brim width ratio of 0.92. Standardised brim perforations are large, at over 300 μm, and are densely-packed at around 10 per sq. mm, forming net-like pattern across brim with around 90% of area being perforated. Brim caecafree. External rim is fine, and there are ridges at top and bottom of marginal band. Prolongations moderately short (exsag.), at under 80% of cephalic length (sag.). In dorsal view, internal rim slanting abaxially at angle of around 450 to posterior border, before curving strongly adaxially. In lateral view, it has weak wave-like profile. Rims meeting just before joining at end of prolongations, to form long genal spine curving adaxially and upwards to follow curve of external rim. Extension of girder meets internal rim 1/3 of way down prolongations. There is no row of large perforations immediately below internal rim. Brim steepens moderately on prolongations to an angle of around 600.

Hypostome, thorax and pygidium not known.

Remarks. Stoloharpes retiarius is the least compliant with the diagnostic characters set out for Stoloharpes in Table 5c. S . retiarius ’s genicranium is slightly wider, its brim is not so steeply sloping, its internal rims in lateral view the have a wave like profile rather than being straight and its brim steepens less on the prolongations. S. retiarius has the other 7 diagnostic characters of its genus shown in Table 5c.

Intraspecies variation shown by the paratypes include variations in perforation sizes, which range from 300 μm to 370 μm, and in the slope of the brim from nearly flat to moderately steep. Brim width ratios are between 0.90 and 1.06.

Stoloharpes retiarius most resembles S. rissaniensis but differs by having: a wider cephalon and genicranium; a glabella that is not so strongly carinated and has a granulated surface; an occipital ring with a granulations; ala anteriorly directed; genal areas with fine pits and granulation; eye lobes with three lenses rather than two; an inner margin of the fringe with a course across the anterior of the genal areas that is more convex than straight and across the anterior of the boss lacks a row of large perforations; an anterior boss that is slightly more inflated; a genal roll sloping more gently laterally, without caeca and perforations that are larger anteriorly; a wider brim that slopes less steeply, has a higher brim width ratio, no caeca, and much larger brim perforations that do not decrease in size away from the girder; a marginal band with ridges top and bottom rather than none; shorter prolongations that in dorsal view slant abaxially before curving adaxially; internal rims that in lateral view have a weak wave like profile rather than a straight profile; an internal rim that meets and joins the external before end of the prolongation; longer genal spines that follow the curve of exterior rim and an extension to the brim that steepens less strongly posteriorly on the prolongations.

Figures

PLATE 51. A–L Helioharpes retiarius n. sp., El Otfal Formation, upper Eifelian, Ottara. A–G dorsal exoskeleton of cephalon only, holotype, NHMUK It 29368 (Fig. 2B, Map 14, site 2). A, dorsal, B, anterior and C, lateral view. Dorsal view of brim perforations: E, F and G lateral view of eye lobe. H–L dorsal exoskeleton of cephalon only, paratype, NHMUK it 29369 (Fig. 2B, Map 14, site 3). I, dorsal, J, lateral and K, anterior view. L, dorsal view of brim perforations. Scale bars shown represent 1 cm unless otherwise indicated.

PLATE 52. A–L Helioharpes retiarius n. sp., El Otfal Formation, upper Eifelian, Ottara. A–F dorsal exoskeleton of a partial cephalon only, paratype, NHMUK It 29367 (Fig. 2B, Map 14, site 1). A, dorsal, B, anterior and C, lateral view. D, antero-dorsal view of genal roll and brim perforations. Dorsal view of E, brim perforations and F, perforations on genal area. G–L dorsal exoskeleton of cephalon only, paratype, NHMUK It 29370 (Fig. 2B, Map 14, site 11). G, dorsal, H, anterior and I, lateral view. J and K, lateral view of eye lobes and L, dorsal view of brim perforations. Scale bars shown represent 1 cm unless otherwise indicated.