Rohrthrips burmiticus, Ulitzka, 2018

Ulitzka, Manfred R., 2018, A first survey of Cretaceous thrips from Burmese amber including the establishment of a new family of Tubulifera (Insecta: Thysanoptera), Zootaxa 4486 (4), pp. 548-558 : 554-555

Rohrthrips burmiticus sp. n.

( Figs 9–12 )

Male: Colour ( Fig. 9 ) uniformly dark brown including antennae and legs; all major setae dark as well as wing veins and fringes; wings shaded greyish-brown.

Head ( Fig. 12 ) with reticulate sculpture at base; longer than wide, with cheeks rounded behind eyes and converging slightly to base; cheeks lacking setae; ocellar setae difficult to assess, one strong pair clearly visible close to base of antennae. Eyes large, their front margin protruding over base of antennae, not prolonged ventrally. Hind ocelli close to compound eyes; far apart from each other. Vertex with two postocular setae far behind eyes. Antennae ( Fig. 11 ) 9-segmented; segments III–VII inverse conically shaped and tapering distally from level of sense cones; segment II apically with a circular sensorium; number of sense cones of the following segments difficult to assess but at least two on III, IV and V; segment IX broadly joined to VIII. Mouth cone ophistognathus; short but pointed; clypeal suture clearly asymmetric. Maxillary palps with two apical setae; short and very likely 2- segmented; labial palps not visible. Maxillary stylets ( Fig. 12 ) slender, deeply retracted into head capsule, extending to base of compound eyes, close together and parallel medially; maxillary bridge not developed. Left mandible strong; right mandible degenerate (a shaded structure possibly its remnant). Pronotum ( Figs 9, 12 ) wider than long, trapezoidal; pronotal chaetotaxy not assessable; epimeral setae long and pointed. Pterothorax as well as basal abdominal segments dented and partly concealed. Fore wings ( Fig. 9 ) becoming progressively larger in distal third; anterior vein complete, reaching costa near apex and bearing setae; second vein not developed, reduced to a faint basal shading; membrane without microtrichia. Fringe cilia straight; arising from sockets ( Fig. 10 ); duplicated cilia present around margin of wing apex and on distal part of posterior margin; sub-basal wing setae at anterior margin lacking; clavus with paired setiform processes at tip ( Fig. 10 ). Hind wing without microtrichia and without any veins; base with recurved setae. Fore legs ( Figs 9, 12 ) with femora stout; fore tarsi with a large tooth. Mid and hind legs slender; all tibiae with one long dorsal seta ( Fig. 9 ); mid and hind tibiae terminally each with one strong spine; mid and hind tarsi two-segmented. Abdominal tergites without wing-retaining setae; lateral setae long and pointed. Abdominal segment IX conical, sternite with clearly visible subgenital plate. Abdominal segment X elongated tubular, with terminal crown of anal setae ( Fig. 9 ).

Measurements. Male (in microns): Body, length 1480 (slightly contracted). Head, length 227; width 201. Eyes, length 107, width 50. Hind ocelli, diameter 19; distance between the hind ocelli 57. Ocellar setae 44. Postocular setae 38. Prothorax, length 258; width 441; epimeral setae 176. Abdomen, length 888 (slightly contracted); largest width 391 (segment IV); segment X (tube), length 189; basal width 50. Antennae, length 422; length (largest width) of segment I 37 (31) [deformed], II 65 (34), III 71 (37), IV 56 (37), V 53 (34), VI 43 (28), VII 50 (22), VIII 31 (16), IX 16 (6). Sense cones, length of inner (outer) on segment III 19 (16), IV 19 (22), V 16 (22); basal width 5–6. Fore wings, length about 1200; largest width 245.

Material studied. Holotype male MU-Fos-53/1 ( Fig. 9 ). Inclusion in Burmese amber, donated to the author by Patrick Müller. Holotype deposited in the Senckenbergische Naturforschende Gesellschaft, Frankfurt am Main, Germany ( SMF T 19282) .

Etymology. The specific epithet ‘ burmiticus ’ refers to the occurrence of the fossil in Burmite.

Discussion. Many features of R. burmiticus sp. n. correspond clearly to those of R. libanicus , particularly with regard to the plesiomorphic characters of the wings mentioned above. The new species, however, has only one vein developed on the fore wings ( Fig. 9 ). Furthermore, it has only one ventral spine on the apex of the hind tibiae, whereas R. libanicus has three (cf. Nel et al. 2010, p. 155, fig. 3). Establishing a new genus based on these differences was rejected. Further findings that allow comparing the head structures of both species may lead to another classification.

Assuming the loss of the wing veins as an apomorphy in the evolution of Tubulifera (Mound et al. 2010), R. burmiticus from the late Cretaceous might be interpreted as more modern than its Mid-Cretaceous sister species (cf. figs 9 and 13). Its phylogenetic position as a direct ancestor of recent Phlaeothripidae or as an evolutionary dead end remains undetermined.

Figures

FIGURES 9–13. FIGURES 9–12. Rohrthrips burmiticus sp. n., holotype male (MU-Fos-53/1). (9) dorsal view; (10) coupling mechanism of the wings, fore wing clavus with paired setiform processus (black arrow), hindwing with basal recurved seta (red arrow); (11) right antenna (segments I and II reconstructed); (12) head and prothorax (md: left mandible, mx: maxillary stylets). FIGURE 13. Rohrthrips libanicus, holotype, right fore wing with two veins (indicated).