Polycytella rasnitsyni, Béthoux & Anderson, 2021

Béthoux, Olivier & Anderson, John M., 2021, The Polycytellidae viewed as Gondwanan Glosselytrodea, Palaeoentomology 4 (6), pp. 550-558 : 555

Polycytella rasnitsyni sp. nov.

( Figs 2 , 3 )

urn:lsid:zoobank.org:act:0D93F67B-6562-44BE-8E7B-8BC4B3A314B8

Holotype. Specimen PRE/F/10559 (preserving a left forewing in ventral aspect and a right forewing in dorsal aspect), Evolutionary Studies Institute , University of the Witwatersrand, Johannesburg, South Africa.

Etymology. The specific epithet honours Alexandr P. Rasnitsyn, for his wide-ranging contribution to the fields of evolutionary entomology and systematics.

Diagnosis. Forewing: length 9.4 mm, aspect ratio 3.6; in the 3 rd quarter of wing length, cells between RA and CuA post wider than long; no intercalary vein between CuA post and CuP (but see above); clavus large (0.7 mm wide opposite clavus mid-length; probably indicative of a large thorax; incompletely known in Polycytella triassica ).

Type locality and horizon. Birds River (locality code ‘Bir 111’; see Anderson & Anderson, 1984), South Africa; Molteno Formation; lower Carnian, Upper Triassic ( Anderson et al., 1998).

Description. A pair of forewings, presumably from the same individual, with left forewing very well preserved, and outline and main veins of right forewing more or less discernible; forewing length 9.4 mm, width 2.6 mm; area between anterior wing margin and ScP broad, with at least 4 rows of small cells; in this area, occurrence of an ambient vein parallel to the anterior wing margin; just distal to the end of ScP, area between anterior wing margin and RA broad (0.6 mm wide opposite the end of ScP), with 4 or 5 rows of cells; area between anterior wing margin and RA gradually tapering, with 2 rows of cells until shortly before the apex; RA simple; MP+CuA ant rectilinear in its basal half, then slightly deflected posteriorly; area between RA and MP+CuA ant broadening from wing base to the ca. 3/5 of wing length, then tapering, with 4 veins at its broadest; area between MP+CuA ant and CuA post broadening from the wing base to the ca. 3/5 of wing length, then tapering, with 3 veins at its broadest; in the 3 rd quarter of wing length, cells between RA and CuA post wider than long; CuA post simple, slightly bent opposite the end of CuP; RA, MP+CuA ant and CuA post joining at their apices and delimiting a single marginal band; claval furrow concave, rectilinear, closely bordered by two convex vein-like elements, the anterior one herein regarded as CuP, the posterior one as AA1 or a derivative of cross-venation (hereafter ‘AA1’); distally, claval furrow and both of these elements barely distinguishable from a single vein, ending 5.4 mm distal to wing base; clavus large (0.7 mm wide opposite clavus mid-length); 2 well-defined AA veins (in addition to AA1), converging towards the end of CuP, with two rows of cells between them, and between AA1 and the first of these veins; area between the second of these AA veins and posterior wing margin with 5 rows of cells, progressively longer than wide towards the margin, and organized into vein-like elements parallel to the posterior wing margin, forming a depression along it.

Discussion. The new material is very similar to Polycytella triassica , particularly in the relatively distal location of the end of CuP (unknown in Mo. parva , see below). Differences mainly regard aspect ratio, the shape of cells in the 3 rd quarter of wing length, and the occurrence, or lack thereof, of an intercalary vein between CuA post and CuP (basal to the end of the latter). Considering that it is more informative to emphasize similarities rather than differences, we propose to assign the new material to the same genus as Polycytella triassica .

The occurrence of intercalary veins running very close to the posterior wing margin, basal to the end of CuP, is probably part of a forewing interlocking mechanism. Indeed, the occurrence of one or several vein-like structures (main and/or intercalary vein(s)) bordering the actual posterior wing margin, basal to the end of CuP or along its entire length, is common in insects with elytrized forewings, such as Dermaptera and some Dictyoptera ( Tillyard, 1931; Nel et al., 2014; Béthoux et al., 2016; Luo et al., in press). Most elaborated cases involve a three-dimensional tongue-and-groove structure, as in Coleoptera ( Breed & Ball, 1908; and see Nachtigall, 1974), which appears as composed of multiple, parallel vein-like elements when viewed dorsally. The bordering of the claval furrow by two vein-like elements (one of the two being CuP) is a configuration that can be observed in elytrized forewings of grasshoppers (OB, pers. observ.), among others. In Polycytella rasnitsyni the interlocking mechanism may have involved the posterior margin of the clavus on one hand, and the area of the claval furrow on the other. Indeed, when folded along the claval furrow, the posterior margin of the clavus of the overlapping forewing overlaps the claval furrow of the overlapped forewing. To best appreciate this the reader is encouraged to cut wings illustrated on Fig. 3 along their margin, use the tip of a pointed blade (or a needle) and a ruler to gently imprint a line of weakness along the claval furrow, and assemble the wing pair in resting position, with the claval furrow forming a 90° angle.

Figures

FIGURE 2. Polycytella rasnitsyni sp. nov., holotype specimen (PRE/F/10559), forewing pair. A, Interpretative drawing (RFW, right forewing; LFW, left forewing). B–D, Photograph and RTI extracts, part. B, Photograph (light-mirrored; ‘cf’, claval furrow). C, RTI extract, specular enhancement mode. D, RTI extract, normals visualisation mode.

FIGURE 3. Polycytella rasnitsyni sp. nov., holotype specimen (PRE/F/10559), interpretative drawings, separated. A, Left forewing, as in Fig. 2A. B, Right forewing, as in Fig. 2A and with reconstructed parts.