﻿The family Polycentropodidae (Insecta, Trichoptera) in mid-Cretaceous Burmese Amber

﻿Abstract Three described species, Neureclipsistriangulasp. nov., Neureclipsisacutasp. nov., and Neureclipsisobtusasp. nov., expand the Neureclipsis cluster to six species dominating the Polycentropodidae in Burmese amber. The new species Plectrocnemiaohlhoffisp. nov. and Plectrocnemiabowangisp. nov. of the Polycentropus cluster add to the comparatively low occurrence of Polycentropodidae in Burmese mid-Cretaceous amber.


Introduction
The caddisfly family Polycentropodidae is one of the most diverse in the trichopteran suborder Annulipalpia and is distributed worldwide, today with about 891 extant species (Chamorro and Holzenthal 2011;Morse 2022). The adults can be distinguished from species of all other families by the following combination of characters: ocelli absent in adult; antennae never longer than forewings; maxillary palpi each five-segmented, first two segments short, each shorter than the third or fourth, the fifth longest and annulated; mesoscutum with a pair of rounded setal warts; mesoscutellum with a rounded setal mesal wart; tibial spurs 2-3/4/4; in male genitalia inferior appendages each one-segmented.
According to Oláh and Johanson (2010), the Polycentropodidae are divided into four diagnostic clusters, based primarily on wing venation and number of spurs on the legs: Neureclipsis cluster, Polycentropus cluster, Cyrnus cluster, and Cyrnodes cluster.
In contrast to the cosmopolitan extant Polycentropodidae, the findings of extinct polycentropodid species are confined to four amber deposits: 1. In Miocene Dominican amber, the family Polycentropodidae is represented by only two species of Cernotina (Wichard 2007;Wichard and Neumann 2021) which belong to the Cyrnodes cluster.
2. In Baltic Pleistocene amber (including findings in Saxonian Bitterfeld amber and Ukrainian Rovno amber), polycentropodids represent the dominant group of fossil caddisflies, accounting for well over 80% of all caddisfly specimens found. According to Ulmer (1912), these polycentropodids belong to 67 extinct species. More recently, several more species have been described from Pleistocene amber deposits (e.g., Mey 1986;Wichard et al. 2009;Ivanov and Melnitsky 2013;Wichard 2013;Melnitsky et al. 2021a, b), increasing the number of species to 118 (Morse 2022).
Most species belong to the genera Holocentropus, Plectrocnemia, and Polycentropus and are assigned to the Polycentropus cluster; other species belong to the genus Nyctiophylax of the Cyrnus cluster. The small Neureclipsis cluster includes only a few species, which are four Neureclipsis species and two Archaeoneureclipsis species which were transferred to the genus Neureclispsis by Oláh and Johanson (2010).
3. From Late Cretaceous Taymyr amber (Siberia, Russian Federation), six polycentropodid species have been described (Botosaneanu and Wichard 1983;Melnitsky and Ivanov 2022a, b). All belong to the extinct genus Archaeopolycentra, which cannot be assigned to any of the extant four diagnostic clusters, sensu Oláh and Johanson (2010).
4. In mid-Cretaceous Burmese amber, eight polycentropodid species have been found belonging to the Neureclipsis and Polycentropus clusters. Of these, five species are described in this paper.

Materials and methods
The amber material was collected by local people in the Hukawng Valley of northern Myanmar, (Myitkyina District, Kachin State) and dates from the middle Cretaceous (Cenomanian) period about 98.8 ± 0.6 Ma ago (Shi et al. 2012), but the geological age of Burmese amber can be expected to be slightly older.
The Burmese amber with the embedded trichopteran inclusions was cut, facegrinded, and polished using a cutting machine and a polishing machine, a RotoPol-25 (Struers), with grinding paper for metallography: 800, 1200, 2500, and 4000 grit. Colour photographs were produced for the documentation of specimens. A Leica M420 macroscope with Apozoom 1:6 was used in combination with a Canon EOS 80D, EOS 3.0 utility software, and Zerene Stacker software. Measurements were made with a Leica SApo ocular micrometer.
Adult caddisflies embedded in amber are slightly flattened and visible in ventral and/or dorsal views. Very rarely forewings and hind wings are separately visible in amber inclusions. The wings are often saddle-roofed and cover the abdomen and genitalia in dorsal and lateral views. The genitalia are visible only in ventral or ventral-lateral views. Therefore, diagnoses and descriptions of male genitalia are usually limited to the ventrally located pair of inferior appendages alone.
Type-specimens in this study are deposited in the following repositories: Type species. Phryganea bimaculata Linnaeus, 1758. Description and diagnosis. Ocelli absent. Filiform antennae no longer than forewings. Maxillary palps each five-segmented with 1 st and 2 nd segments much shorter than 3 rd segment, terminal segment longest, annulated, and flexible. Neureclipsis species have complete wing venations with apical forks I, II, III, (IV), V on forewings and apical forks I, II, III, V on hind wings. In fore-and hind wings, fork I petiolate, fork II sessile, discoidal cell subtriangular, closed, crossvein m sloping. In forewings medial and thyridial cells usually present. Tibial spur formula 3/4/4.

NIGP
Neureclipsis is distinguished from all other polycentropodid genera, except Neucentropus, by the presence of folk III in the hind wings. The following three new Neureclipsis species differ in their forewing lengths and in the number of their flagellomeres but are characterized especially by the male genitalia, clearly in the inferior appendages, which are one-segmented, long, and monolobed.
Neureclipsis triangula sp. nov. https://zoobank.org/8F917EDA-F2C2-4193-9AA2-C185281408EE Fig. 1 Diagnosis. The extinct species Neureclipsis triangula sp. nov. is characterized by a pair of slightly cupped inferior appendages running parallel in ventral view. Each appendage is tapered at the base, wider near the middle and apically forming a sub-triangular shape. Its sloping apical edge is clearly subapically toothed and highlighted in black.
Holotype. ♂; Myanmar, Kachin State, Hukawng Valley; exact locality unknown; Mid-Cretaceous Burmese amber inclusion; deposited in the amber collection of the NIGP; NIGP200021. Description. Genus as described above. Body well preserved and visible in ventral and dorsal views. Forewing length about 4.2 mm, oblong, rounded, light brown. Antennae about two-thirds as long as forewings, with about 36 flagellomeres plus scapus and short pedicellus. Inferior appendages having subtriangular shape, with oblique, subapically toothed, and black terminal margin.
Holotype. ♂; Myanmar, Kachin State, Hukawng Valley; exact locality unknown; Mid-Cretaceous Burmese amber inclusion; deposited in the amber collection of the NIGP; NIGP200022. Description. Genus as described above. Body well preserved and visible in ventral and dorsal view, dorsum partially covered by dark artefacts. Forewing length about 3.0 mm, rounded, light brown. Antennae two-thirds as long as forewings with about 24 flagellomeres plus scapus and pedicellus. Inferior appendages long, bearing black, beak-shaped cap apically.
Neureclipsis obtusa sp. nov. https://zoobank.org/10D154EC-1DD9-40B0-A88E-F2285CE3FAA5 Fig. 3 Diagnosis. The extinct species Neureclipsis obtusa sp. nov. has a distinctive pair of rodshaped, long, inferior appendages. Apically, each appendage ends with an oblique oval surface, on which there a few, scattered stout bristles on the oval and a cluster of small setae on the edge of the oval.
Holotype. ♂; Myanmar, Kachin State, Hukawng Valley; exact locality unknown; Mid-Cretaceous Burmese amber inclusion; deposited in the amber collection of the NIGP; NIGP200023. Description. Genus as described above. Body well preserved and visible in ventral and dorsal views, dorsum slightly decomposed. Forewing length about 3.5 mm, broad and rounded, light brown. Antennae as long as forewings, with about 42 flagellomeres plus scapus and pedicellus. Inferior appendages long, parallel-sided, apically with oblique oval surface.
Description and diagnosis. Ocelli absent. Filiform antennae about as long as forewings or shorter. Maxillary palps each five-segmented with the 1 st and 2 nd segments much shorter than the 3 rd segment, terminal segment longest and annulated. Plectrocnemia adults with complete forewing venation, apical forks I, II, III, IV, V present; fork I petiolate and fork II sessile; discoidal and median cells closed; crossveins r, s, r-m, and m usually present. In hind wings apical forks I, II, V present, fork I petiolate and fork II sessile; discoidal cell closed. Tibial spur formula 3/4/4.
The two new Plectrocnemia species are very similar and differ clearly in the onesegmented inferior appendages which are robust and short or long.

Plectrocnemia ohlhoffi sp. nov.
https://zoobank.org/6FE60CF6-492D-4E0D-A7E8-EB1535E863E6 Fig. 4 Diagnosis. The extinct species Plectrocnemia ohlhoffi sp. nov. is characterized by a pair of elongate inferior appendages, slightly diverging distally and slightly curved apically toward each other. The appendages are weakly concave mesally along their length. In ventral view, each appendage is rounded at the apex and slightly concave in shape apicolaterally, each with a subapical tooth and a weakly projecting apicomesal corner.
Etymology. The fossil species is dedicated to Rainer Ohlhoff, who donated the type specimen to the Zoological Research Museum Alexander Koenig, Bonn, Germany (ZFMK) for permanent preservation.
Holotype. ♂; Myanmar, Kachin State, Hukawng Valley; exact locality unknown; Mid-Cretaceous Burmese amber inclusion; deposited in the amber collection of the ZFMK; former Rainer Ohlhoff collection; ZFMK-TRI000834. Description. Genus as described above. Body well preserved, visible in left ventrolateral view. Forewing length about 4.2 mm. Forewings hyaline, light brown. Antennae about two-thirds as long as forewings with about 30 flagellomeres plus scapus and pedicellus; left antenna incomplete. Inferior appendages elongate, each forming an elongate shell and both inclining towards the genital midline.

Plectrocnemia bowangi sp. nov.
https://zoobank.org/0A4CBE34-C7B9-425E-8C91-994D9B01AAB6 Fig. 5 Diagnosis. The extinct species Plectrocnemia bowangi sp. nov. is characterized by a pair of spoon-like inferior appendages. On the inner side of each of the two spoon-shaped appendages there is a long needle, the tips of which touch each other in about the middle of the genital space.

Conclusions
Polycentropodids are found only sporadically in Burmese amber. This fact is especially true in comparison to the numerous polycentropodid specimens in Eocene Baltic amber, which belong to the Polycentropus cluster and its genera Plectrocnemia, Polycentropus, and Holocentropus, and also to the genus Nyctiophylax in the Cyrnus cluster (Ulmer 1912;Wichard et al. 2009). Species of the Neureclipsis cluster predominate in the Burmese Amber. The cluster includes the genus Neucentropus with an extinct amber species (N. macularis) and an extant species that now occurs in southern Russian Far East, Mongolia, China, Vietnam, and Japan (Li et al. 1998;Morse et al. 2019), and also an extinct amber genus Electrocentropus (E. dilucidus) with the characteristically absent fork IV of the forewings (Wichard 2021), as well as the genus Neureclipsis of which four fossil species currently are known to occur in Burmese amber.
Additional Neureclipsis species are expected in the near future, as some amber inclusions indicate the Neureclipsis cluster, but the limited state of preservation of amber does not always allow for careful taxonomic analysis and description.