Polycytellidae Martynova, 1952

Béthoux, Olivier & Anderson, John M., 2021, The Polycytellidae viewed as Gondwanan Glosselytrodea, Palaeoentomology 4 (6), pp. 550-558 : 551-552

Family Polycytellidae Martynova, 1952 stat. rest.

Type genus. Polycytella Tillyard, 1922 (including Polycytella triassica Tillyard, 1922 , Triassic, Australia; and Polycytella rasnitsyni sp. nov., Triassic, South Africa).

Other genera. Argentinoglosselytrina Martins- Neto & Gallego, 2001 (including Argentinoglosselytrina pulchella Martins-Neto and Gallego, 2001 , Triassic, Argentina), and Moltenojurina gen. nov. (including Moltenojurina parva sp. nov., Triassic, South Africa).

Emended diagnosis. Forewing: opposite the end of ScP, area anterior to RA large (accounting for about a quarter of wing width).

Discussion. Genera herein assigned to the Polycytellidae display two states that have been generally regarded as relevant to the systematics of Glosselytrodea , namely:

(1)occurrence of a single mid-vein (or, ‘two mid-veins fused into a single mid-vein, as opposed to ‘occurrence of two, closely adjoined but distinct, mid-veins’); and

(2) anterior and posterior ambient veins joining each other at their apices (as opposed to ‘anterior and posterior ambient veins reaching the anterior and posterior margins, respectively’).

Martynova (1952; and see Martynova, 1962, 1991) regarded these traits as diagnostic of the Polycytellidae , to which she also assigned Mesojurina Martynova, 1943 (including Mesojurina sogjutensis Martynova, 1943 , Jurassic, Kyrgyzstan; and see below). However, Rasnitsyn & Aristov in Aristov et al. (2013) considered that this combination of traits may have been acquired convergently within two distinct families, namely the oligoneurous Jurinidae Zalessky,1929 and the polyneurous Glosselytridae Martynov, 1938 . Besides the number of veins, which can be partly related to size, this proposal rests on scenarios of forewing elytrization, achieved either by membrane strengthening or veins strengthening. However, these aspects remain difficult to appreciate based on data currently available on Glosselytrodea .

Of further interest, it is common that the area between the anterior wing margin and ScP is enlarged in Glosselytrodea . Consequently, the anterior wing margin has a marked inflexion opposite the end of ScP. However, in genera herein assigned to the Polycytellidae , the area anterior to RA (i. e., between ScP and RA and then between the anterior wing margin and RA) is also enlarged (opposite the end of ScP, nearly as large as the area between RA and MP+CuA ant), with the consequence that the anterior wing margin regains a more continuous course. This trait can be described as follows:

(3) ‘opposite the end of ScP, area anterior to RA large’ (as opposed to ‘RA close to ScP and, distal to the end of this vein, close to the anterior wing margin’).

It is present in Polycytella ( Fig. 1 ), Argentinoglosselytrina and the new material described below ( Figs 2–4 ). This trait is most likely derived, as it is unique among Glosselytrodea and, to our knowledge, winged insects as a whole. A seemingly similar condition occurs in Blattodea, in which the area between the anterior wing margin and the stem of R is often very wide ( Rehn, 1951). However, this R stem emits successive anterior branches, the anterior-most ones belonging to RA.As a consequence, the actual area between ScP and RA corresponds to the area between ScP and the first anterior branch of R, and is narrow. The conditions in Polycytellidae and Blattodea are therefore not homologous.

Considering that Mesojurina displays the plesiomorphic condition of the character (viz., the state ‘RA close to ScP and, distal to the end of this vein, close to the anterior wing margin’), we therefore exclude this genus from the Polycytellidae , which, as a consequence, is strictly Gondwanan. Whether the corresponding taxon shall better be considered a subfamily to be nested within Jurinidae or Glosselytridae remains to be elucidated.

Figures

FIGURE 1. Polycytella triassica Tillyard, 1922, holotype specimen (GSQ81a), right forewing (dorsal aspect, but mostly as impression of ventral side). A, Interpretative drawing. B, Photograph (G. Thompson, Queensland Museum, Brisbane, Australia; ‘cf’, claval furrow).

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.

FIGURE 4. Moltenojurina parva gen. et sp. nov., holotype specimen (PRE/F/20922), right forewing. A, Interpretative drawing. B, Photograph (light-mirrored, flipped horizontally).