Cretophengodidae, a new Cretaceous beetle family, sheds light on the evolution of bioluminescence

Abstract

Bioluminescent beetles of the superfamily Elateroidea (fireflies, fire beetles, glow-worms) are the most speciose group of terrestrial light-producing animals. The evolution of bioluminescence in elateroids is associated with unusual morphological modifications, such as soft-bodiedness and neoteny, but the fragmentary nature of the fossil record discloses little about the origin of these adaptations. We report the discovery of a new bioluminescent elateroid beetle family from the mid-Cretaceous of northern Myanmar (ca 99 Ma), Cretophengodidae fam. nov. Cretophengodes azari gen. et sp. nov. belongs to the bioluminescent lampyroid clade, and would appear to represent a transitional fossil linking the soft-bodied Phengodidae + Rhagophthalmidae clade and hard-bodied elateroids. The fossil male possesses a light organ on the abdomen which presumably served a defensive function, documenting a Cretaceous radiation of bioluminescent beetles coinciding with the diversification of major insectivore groups such as frogs and stem-group birds. The discovery adds a key branch to the elateroid tree of life and sheds light on the evolution of soft-bodiedness and the historical biogeography of elateroid beetles.

Full text

royalsocietypublishing.org/journal/rspb
Research
Cite this article: Li Y-D, Kundrata R, Tihelka
E, Liu Z, Huang D, Cai C. 2021
Cretophengodidae, a new Cretaceous beetle
family, sheds light on the evolution of
bioluminescence. Proc. R. Soc. B 288:
20202730.
https://doi.org/10.1098/rspb.2020.2730
Received: 31 October 2020
Accepted: 17 December 2020
Subject Category:
Palaeobiology
Subject Areas:
evolution, palaeontology
Keywords:
Elateroidea, biogeography, fossil,
bioluminescence, Cretaceous Terrestrial
Revolution
Author for correspondence:
Chenyang Cai
e-mail: cycai@nigpas.ac.cn
Electronic supplementary material is available
online at https://doi.org/10.6084/m9.figshare.
c.5253502.
Cretophengodidae, a new Cretaceous
beetle family, sheds light on the
evolution of bioluminescence
Yan-Da Li1,2, Robin Kundrata3, Erik Tihelka4, Zhenhua Liu5,6, Diying Huang1
and Chenyang Cai1,4
1
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, and
Centre for Excellence in Life and Palaeoenvironment, Chinese Academy of Sciences, Nanjing 210008,
People’s Republic of China
2
School of Life Sciences, Peking University, Beijing 100871, People’s Republic of China
3
Department of Zoology, Faculty of Science, Palacký University, 77900 Olomouc, Czech Republic
4
School of Earth Sciences, University of Bristol, Life Sciences Building, Tyndall Avenue, Bristol BS8 1TQ, UK
5
State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-Sen University, Guangzhou 510275,
People’s Republic of China
6
Australian National Insect Collection, CSIRO National Research Collections Australia, GPO Box 1700, Canberra,
Australian Capital Territory 2601, Australia
Y-DL, 0000-0002-9439-202X; RK, 0000-0001-9397-1030; ET, 0000-0002-5048-5355;
ZL, 0000-0002-2739-3305; DH, 0000-0002-5637-4867; CC, 0000-0002-9283-8323
Bioluminescent beetles of the superfamily Elateroidea (fireflies, fire beetles,
glow-worms) are the most speciose group of terrestrial light-producing animals.
The evolution of bioluminescence in elateroids is associated with unusual
morphological modifications, such as soft-bodiedness and neoteny, but the
fragmentary nature of the fossil record discloses little about the origin of
these adaptations. We report the discovery of a new bioluminescent elateroid
beetle family from the mid-Cretaceous of northern Myanmar (ca 99 Ma),
Cretophengodidae fam. nov. Cretophengodes azari gen.etsp.nov.belongsto
the bioluminescent lampyroid clade, and would appear to represent a transi-
tional fossil linking the soft-bodied Phengodidae + Rhagophthalmidae clade
and hard-bodied elateroids. The fossil male possesses a light organ on the abdo-
men which presumably served a defensive function, documenting a Cretaceous
radiation of bioluminescent beetles coinciding with the diversification of
major insectivore groups such as frogs and stem-group birds. The discovery
adds a key branch to the elateroid tree of life and sheds light on the evolution
of soft-bodiedness and the historical biogeography of elateroid beetles.
1. Introduction
Bioluminescence, the production of light by living organisms, evolved over 30
times independently on diverse branches of the tree of life including unicellular
algae, cnidarians, fishes and marine annelid worms [1]. On land, light-producing
beetles are the most widespread and abundant bioluminescent organisms [2,3];
their elaborate flash displays play a role in mate recognition as well as in
aposematic signalling, communication and luring prey [4–6]. The majority of
bioluminescent beetles (approx. 2300 species) belong to the megadiverse poly-
phagan superfamily Elateroidea and have been grouped into a single clade by
recent molecular studies: the elaterid-lampyroid clade, i.e. Elateridae (click
beetles, fire beetles), Sinopyrophoridae, Lampyridae (fireflies), Phengodidae
(glow-worm beetles) and Rhagophthalmidae [3,7–11]. The evolution of biolumi-
nescence in beetles is associated with a number of unusual morphological
modifications such as soft-bodiedness and extremely modified neotenic females
that retain larviform features into adulthood [10,17], but little is known about the
transitions leading to the evolution of these peculiar morphologies and modes of
life since the fossil record of soft-bodied elateroids is exceedingly scarce.
© 2021 The Author(s) Published by the Royal Society. All rights reserved.

Within the bioluminescent lampyroid clade, Phengodidae
and Rhagophthalmidae were traditionally considered to be clo-
sely related based on morphological evidence [18,19], and
indeed, they have been regularly recovered as sister groups
in recent molecular phylogenies [7,9,12,14]. Rhagophthalmidae
is a relatively small group of beetles occurring mainly in the
East Palearctic and Oriental regions, with about 60 species
describedtodate[20].ThemorespeciosePhengodidae
includes nearly 300 species, with the centre of diversity in the
Neotropical region [21], and the isolated subfamily Cydistinae
distributed in West Asia. Although fossil Lampyridae have
been reported from Cretaceous Burmese amber and a few Cen-
ozoic deposits [22–25], fossils belonging to the Phengodidae +
Rhagophthalmidae clade remain unknown. Here, we describe
Cretophengodes azari gen. et sp. nov., based on a specimen pre-
served in mid-Cretaceous amber from northern Myanmar. The
peculiar genus is classified in a new family, Cretophengodidae,
belonging to the specialized bioluminescent lampyroid clade.
This fossil possesses an intriguing combination of characters,
shedding light on the early evolution of the lampyroid clade
and the origin of bioluminescence in beetles.
2. Systematic palaeontology
Order Coleoptera Linnaeus, 1758
Suborder Polyphaga Emery, 1886
Superfamily Elateroidea Leach, 1815
Cretophengodidae Li, Kundrata, Tihelka and Cai fam. nov.
Type genus. Cretophengodes gen. nov.
Diagnosis (male). Mandibles slender, sickle-shaped. Fron-
toclypeal region moderately declined anteriorly. Eyes large,
strongly protruding. Antennae 12-segmented; antennomere
1 stout, expanding apically; antennomeres 2 and 3 short;
antennomeres 4–11 elongate, bipectinate. Prosternum in front
of coxae longer than diameter of procoxal cavity. Prosternal
process narrow and elongate, acute apically, reaching posterior
edge of procoxae. Elytra oblong, sub-parallel sided, nearly com-
pletely covering abdomen, leaving at most only apex of ultimate
tergite exposed. Tarsal formula 5-5-5; tarsomeres 2–4eachwith
membranous lobe. Abdomen with six apparently immovable
ventrites; photic organ present on median portions of the
basal three abdominal ventrites.
Composition and distribution. Monogeneric, with Creto-
phengodes gen. nov. known only from mid-Cretaceous
Burmese amber.
Cretophengodes Li, Kundrata, Tihelka and Cai gen. nov.
Type species. Cretophengodes azari sp. nov., here designated.
Etymology. The generic name is derived partly from
‘Cretaceous’, in reference to the age of the fossil, and the
genus Phengodes, the type genus of the morphologically simi-
lar and presumably closely related Phengodidae. The gender
is masculine.
Diagnosis. As for the family with additional characters:
body moderate (approx. 7.3 mm long); pronotum sub-pentago-
nal, wider than long; elytra irregularly punctate, with several
raised interstrial intervals forming indistinct carinae; claws
simple.
Cretophengodes azari Li, Kundrata, Tihelka and Cai sp. nov.
Figures 1a,band 2.
Etymology. After Prof. Dany Azar, palaeoentomologist
extraordinaire.
(a)(b)(e)(f)
(c)(d)
Figure 1. General habitus of Cretophengodidae and representatives of the closely related Phengodidae and Rhagophthalmidae, under incident light.
(a,b)Cretophengodes azari gen. et sp. nov., dorsal and ventral views, respectively, with arrowhead showing the photic organ. (c,d)Zarhipis sp. (Phengodidae),
dorsal and ventral views, respectively. (e,f)Rhagophthalmus sp. (Rhagophthalmidae), dorsal and ventral views, respectively. Scale bars: (a,b,e,f) 2 mm;
(c,d) 4 mm. (Online version in colour.)
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2

Type material. Holotype, NIGP173775, male, mid-Cretac-
eous (upper Albian to lower Cenomanian [26,27]), from amber
mine near Noije Bum Village, Hukawng Valley, Tanai Township,
Myitkyina District, Kachin State, northern Myanmar.
Diagnosis. As for the genus.
Description. For a full description of Cretophengodes azari
gen. et sp. nov., refer to the electronic supplementary material.
3. Discussion
(a) Systematic placement of Cretophengodes
Cretophengodes possesses a unique combination of characters
within Elateroidea, including antennae with 12 antenno-
meres, which are bipectinate from antennomere 4, a
relatively long prosternal process, and six abdominal ven-
trites in males (figure 2c–e). Within Elateroidea, only a few
groups have 12-segmented bipectinate (or bilamellate) anten-
nae, including Asiopsectra (Brachypsectridae), Elateridae,
Rhagophthalmidae and most Phengodidae. Although some
other lineages like Lampyridae and Eucnemidae also contain
species with bipectinate antennae, these do not consist of 12
antennomeres [28]. The antennae of Asiopsectra and Elateri-
dae are more lamellate, relatively flat and short [29], while
in Cretophengodes the rami are much longer and more slender.
In Rhagophthalmidae, the antennomere 3 is longer than
antennomere 2, and possesses rami if the antennae are bipec-
tinate (electronic supplementary material, figure S2) [30]. On
the contrary, Phengodidae, as well as Cretophengodes,have
antennomere 3 short and simple, and the long and slender
rami begin from antennomere 4 [30,31]. Just like males of
Phengodidae and Rhagophthalmidae, Cretophengodes pos-
sesses a putative photic organ on the abdominal ventrites
which is preserved as a white foamy layer on abdominal ven-
trites 1–3 (figure 1b). The region of the abdomen bearing the
light organ corresponds well to the appearance of photic
organs in modern Phengodidae and Rhagophthalmidae
males (e.g. fig. 8 in [31]).
(a)(c)
(d)
(b)
(e)(f)
(g)(h)
Figure 2. Details of Cretophengodes azari gen. et sp. nov., under epifluorescence. (a) Head, dorsal view. (b) Head, ventral view. (c) Prothorax, ventral view.
(d) Abdomen, ventral view. (e) Antenna, dorsal view. ( f) Mesothorax, ventral view. (g) Elytra, dorsal view. (h) Prothorax, dorsal view. Abbreviations: a1–4,12,
antennomeres 1–4,12; an, antenna; el, elytron; ey, compound eye; lbp, labial palp; md, mandible; msc, mesocoxa; msv, mesoventrite; mtf, metafemur; mttb,
metatibia; mtts, metatarsus; mtv, metaventrite; mxp, maxillary palp; pf, profemur; pn, pronotum; ps, prosternum; ptb, protibia; pts, protarsus; sc, scutellum;
v1–6, ventrites 1–6. Scale bars: 500 µm. (Online version in colour.)
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3

Morphologically, Cretophengodes resembles extant Phen-
godidae (figure 1c) in its head structures (including
antennae and sickle-shaped mandibles) and pronotal shape
(figure 2b). However, other characters of Cretophengodes are
distinctly different from extant Phengodidae. The position
of the abdominal photic organ medially at the basal abdomi-
nal ventrites is more similar to the arrangement in the
rhagophthalmid genus Diplocladon than to any species in
Phengodidae. The long prosternal process of Cretophengodes
is typical of well-sclerotized elateroids, in which it usually
reaches at least to the posterior edge of procoxae (figure 2c).
By contrast, most soft-bodied elateroids, including Phengodi-
dae, have an incomplete or reduced prosternal process
[32,33]. Additionally, the prosternum in front of the coxae is
very short in most Phengodidae and Rhagophthalmidae,
often forming a very narrow transverse bar (figure 1d,f),
whereas in Cretophengodes the prosternum in front of coxae
is not shortened, being longer than the shortest diameter of
the procoxae (figure 2c). The non-shortened prosternum is
present only in the Asian Cydistinae, which, however, have
a considerably reduced prosternal process [30]. All extant
lineages of Phengodidae share the frontal partly membranous
and reduced mesoventrite, whereas in Cretophengodes it is
well-developed and sclerotized. Similarly, the elytra are
slightly to extremely shortened in Phengodidae and some
Rhagophthalmidae, exposing several to all abdominal ter-
gites, whereas in Cretophengodes, the tergites are nearly
completely covered by the elytra, with only the apical portion
of last visible tergite exposed, which may, however, be caused
by compression during fossilization (for similar preservation,
see [34]). An additional character distinguishing Cretophen-
godes from Phengodidae is the number of abdominal
ventrites. This character has been widely used for differentiat-
ing various elateroid families, and varies from five connate
ventrites in some hard-bodied groups to seven or eight free
ventrites connected by extensive membranes in the soft-
bodied families [33]. In the male of Cretophengodes, the six
ventrites are not connected by membranes, giving the abdo-
men a rather compact appearance (figures 1band 2d).
Males of Phengodidae and Rhagophthalmidae, however,
have eight very freely connected ventrites, such that the
abdomen is capable of considerable stretching.
The unique combination of characters in Cretophengodes is
unknown in any currently defined beetle lineage. Therefore,
Cretophengodes deserves family status in Elateroidea, and
due to shared morphological features with Phengodidae,
we hypothesize its position in the previously defined lampyr-
oid clade [7–9]. Taking into account its divergent
morphology, shared characters with Rhagophthalmidae and
the hard-bodied elateroids, and the dramatic change that
would necessitate for the morphological diagnosis of Phen-
godidae, we prefer to accommodate the new genus as a
separate family. We hypothesize that Cretophengodidae
probably represents a stem group of Phengodidae + Rha-
gophthalmidae (figure 3; electronic supplementary material).
(b) Evolution of beetle bioluminescence: timing
and drivers
Beetles of the lampyroid clade (Sinopyrophoridae, Phengodi-
dae, Rhagophthalmidae and Lampyridae) are rare in the
fossil record. The earliest fossil belonging to the group is a lam-
pyrid from Burmese amber that possesses an abdominal photic
organ [25], while no fossils belonging to the Phengodidae +
Rhagophthalmidae clade have been reported previously. Our
discovery of Cretophengodidae confirms that beetles of the bio-
luminescent lampyroid clade begun to diversify by at least the
mid-Cretaceous, during a period of biotic turnover associated
with the radiation of angiosperms known as the Cretaceous
Terrestrial Revolution (KTR) [35]. This helps to narrow the
previous molecular clock estimates of the origin of the Phengo-
didae+ Rhagophthalmidae clade, which range from the Late
Cretaceous to Palaeogene (95% CI from 116 to 59 Ma [8]).
In elateroids, bioluminescence is more widespread in the
immature stages than in adults [19,36]. Larvae of bioluminescent
groups emit light when disturbed or glow spontaneously in
slow pulses or continuously at night [5,37]. Glowing larvae are
avoided by some predators [4], leading some workers to postu-
late that bioluminescencefirst evolved as a defensive mechanism
and was only later co-opted as a mating and communication
150 125 100 75 50 25
0
Ma
Elateridae
Sinopyrophoridae
Lampyridae
Phengodidae
Rhagophthalmidae
Jur. Cretaceous Palaeogene Neo.
lampyroid clade
1
2
3
4
5
†Cretophengodidae
Q.
Figure 3. Hypothesized phylogenetic relationships within the lampyroid clade, with Cretophengodidae as sister to Phengodidae + Rhagophthalmidae. Node 1:
frontoclypeus strongly and abruptly declined, lateral portion of prosternum 0.5–2.0 times as long as the length of procoxal cavity. Node 2: bioluminescence.
Node 3: clicking mechanism lost, soft-bodied, females neotenic (exceptions in some Lampyridae). Node 4: head never fully concealed from above by pronotum,
bipectinate or bilamellate 12-segmented antennae (exceptions in some Rhagophthalmidae and Phengodidae), labral apex emarginate. Node 5: prosternum in front
of procoxae very short (exceptions in Phengodidae: Cydistinae), prosternal process incomplete or reduced, males with eight abdominal ventrites, abdominal ventrites
separated by membranes. Abbreviations: Jur., Jurassic; Neo., Neogene; Q., Quaternary. Tree topology after Kusý et al. [9]. (Online version in colour.)
royalsocietypublishing.org/journal/rspb Proc. R. Soc. B 288: 20202730
4

signal in adults [5,19,36,38,39]. The function of bioluminescence
in adults of Phengodidae and Rhagophthalmidae, which pro-
duce a range of colours from green to red, is poorly
understood. Light production in southern American Phengodi-
dae adults does not appear to play a role in searching for mates,
since a bioluminescent display only occurs during mating, so a
defensive function seems likely [40]. Likewise, Rhagophthalmus
males (figure 1e) are luminescent only shortly after eclosion
and so light production is not used in courtship [41]. This
indicates that Cretophengodidae adults may have produced
light primarily for defence, although we cannot rule out the
possibility that it also functioned as a mating signal.
Today, major predators of soft-bodied elateroids include
invertebrate groups such as spiders and ants as well as ver-
tebrates such as frogs and birds [42–44]. Crucially, several
of these groups may have initially driven the evolution of bio-
luminescence in beetles diversifying during the KTR. The
earliest ants are known from Cretaceous amber deposits and
stem-group ants co-occurred with Cretophengodes in the
Burmese amber forest [45,46]. Major clades of frogs (Anura)
originated in the Early Cretaceous and the group became
morphologically diverse during this period [47,48]. Cretaceous
stem-group birds (Enantiornithes) included insectivores
specialized for feeding on soft-bodied arthropods [49,50],
and are also known from Burmese amber [51,52]. These visu-
ally hunting predators may have provided a strong selection
pressure favouring the evolution of defensive bioluminescence
in elateroids during the Cretaceous.
(c) Biogeography of the Phengodidae +
Rhagophthalmidae clade
Extant species of Rhagophthalmidae occur mainly in eastern
and southeastern Asia [53]. Phengodidae, however, display a
disjunct distribution pattern. The phengodid subfamily Cydis-
tinae is known exclusively from West Asia [30], while the
remaining and more speciose phengodid subfamilies Phengo-
dinae and Mastinocerinae occur throughout the New World
from southern Canada to Chile ( figure 4) [31,54,55].
Our discovery of Cretophengodes, the first fossil putatively
belonging to the Phengodidae + Rhagophthalmidae clade,
supports the hypothesis that the clade originated in the Old
World. Under this scenario, the diversity of Phengodidae in
the New World resulted from intercontinental dispersal and
subsequent local diversification. Both Rhagophthalmidae
and Phengodidae are neotenic, with adult females retaining
a larviform morphology, which contributes to their extremely
limited dispersal ability [56]. Our finding nevertheless
would demonstrate that neotenic lineages are capable of
long-distance dispersal over long geological time scales.
Kusý et al. [9] suggested that the lampyroid clade originated
in eastern Laurasia, citing an unpublished Phengodidae fossil in
Burmese amber as supporting evidence. However, this appears
to be problematic in light of our new discovery as well as the
palaeobiogeography of Burmese amber fossils. Although
historically the Burma Terrane was considered as part of Laur-
asia [57], the biota of Burmese amber indicates a Gondwanan
affinity of the Burma Terrane [58]. A recent palaeomagnetic
study further confirmed that the Burma Terrane was probably
an isolated island at near-equatorial latitude during the mid-
Cretaceous [59]. Hence, the possible presence of Phengodidae
fossils in Burmese amber cannot be regarded as supporting
evidence of a Laurasian origin of the lampyroid clade.
(d) Evolution of soft-bodiedness in Elateroidea
Elateroids were traditionally divided into two major groups,
the strongly sclerotized Elateroidea sensu stricto and the
soft-bodied Cantharoidea [14,15]. Recent molecular studies,
however, firmly reject the monophyly of Cantharoidea [4,5,8],
indicating that the shared morphological traits of soft-bodied
elateroid beetles were acquired several times independently
in their evolutionary history [8,9]. Moreover, the differences
between hard- and soft-bodied elateroids are often not evident.
Instead, there is a continuum from fully sclerotized lineages to
extremely soft-bodied ones with neotenic forms [12].
The newly discovered male specimen of Cretophengodes is a
good example documenting such gradual change in the
Rhagophthalmidae
extant
Cretophengodes
mid-Cretaceous
Cydistinae
extant
Phengodinae + Mastinocerinae
extant
Figure 4. Geographical distribution of Cretophengodidae (genus Cretophengodes), Phengodidae (subfamilies Cydistinae, Mastinocerinae and Phengodinae) and
Rhagophthalmidae. World map adapted from Natural Earth (NaturalEarthData.com). (Online version in colour.)
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5

evolution towards soft-bodiedness in the Phengodidae +
Rhagophthalmidae lineage. Since both Phengodidae and
Rhagophthalmidae have extremely soft body cuticles and
variously modified morphologies tied with neoteny, Cretophen-
godes represents an intermediate form between hard- and soft-
bodied groups. In well-sclerotized elateroids, the prosternal
process is complete and fits into a deep mesoventral cavity
[32], forming a clicking mechanism that enables beetles lying
on their dorsal side to jump and land on their legs or escape pre-
dators. In most soft-bodied groups, such as Phengodidae
and Rhagophthalmidae, the prosternal process is reduced or
completely absent [53,54]. However, the prosternum of male
Cretophengodes is well-developed, with the prosternal process
elongate and narrow, although it probably does not reach the
mesoventral cavity. Besides, most well-sclerotized elateroids
have five abdominal ventrites (sternites III–VII), with usually at
least the basal four connate. By contrast, most soft-bodied elater-
oids usually have seven or eight free ventrites, so that the
sternites II, VIII and IX are also exposed [33]. Due to the presence
of well-developed membranes between the individual segments,
soft-bodied elateroids have very flexible abdomens, capable of
twistingandstretchingthataresometimesextendbeyondthe
elytra. The six ventrites in male Cretophengodes do not seem to
be flexible, representing an intermediate stage. The presence of
six ventrites in males was previously known only in the elaterid
tribe Cebrionini [60]. Notably, in the recently described South
American family Jurasaidae, another elateroid family that com-
bines characters of hard- and soft-bodied lineages, males have
only five but freely connected ventrites [16], which indicates
that the increase of ventrite number and disconnection of indi-
vidual ventrites occurred in different soft-bodied lineages in
different sequences during the evolution of the group.
The females of Cretophengodidae remain unknown.
However, given that all known females of their presumable
relatives (i.e. Phengodidae and Rhagophthalmidae) are
more or less larviform [53,54], it is plausible that female
Cretophengodidae were neotenic as well (figure 5). The
neotenic adult females may be easily misidentified as larvae
and therefore ignored by researchers unfamiliar with this
particular group. Even in extant neotenic groups, females
are much less represented in collections or are not known
at all [15,30,61]. Therefore, more attention should be paid to
larviform beetle fossils, which could be crucial for improving
our understanding of the evolution of soft-bodiedness
in beetles.
4. Material and methods
The Burmese amber specimen studied here originates from
amber mines near the Noije Bum Hill (26°20’N, 96°36’E),
Hukawng Valley, Kachin State, northern Myanmar. The speci-
men is deposited in the Nanjing Institute of Geology and
Palaeontology (NIGP), Chinese Academy of Sciences at Nanjing,
China. The amber piece was trimmed with a small table saw,
ground with emery papers of different grit sizes, and finally
polished with polishing powder.
Photographs under incident light were taken with a Zeiss
Discovery V20 stereo microscope. Widefield fluorescence images
were captured with a Zeiss Axio Imager 2 light microscope com-
bined with a fluorescence imaging system. Confocal images
were obtained with a Zeiss LSM710 confocal laser scanning micro-
scope. Images under incident light and widefield fluorescence
were stacked in Helicon Focus 7.0.2 or Zerene Stacker 1.04. Confo-
cal images were manually stacked in Adobe Photoshop CC.
Images were further processed in Adobe Photoshop CC to
enhance contrast. The classification of Elateroidea follows Kun-
drata et al. [12] and Kusý et al. [9], the classification and limits of
Phengodidae follow Kundrata et al. [30] and morphological
terminology is adapted from Costa & Zaragoza-Caballero [54].
Nomenclatural acts. This published work and the nomenclatural acts have
been registered in ZooBank. The LSID for this publication is urn:lsid:
zoobank.org:pub:FB7D9187-835C-4B32-86DE-A6B2E37A8812.
Data accessibility. The supplementary descriptions and figures support-
ing this article have been uploaded as the electronic supplementary
material. The original series of confocal slices are available on
Zenodo repository (doi:10.5281/zenodo.4313770).
Authors’contributions. C.C. and Y.-D.L. conceived the study, Y.-D.L., Z.L.
and R.K. processed the photomicrograph data. Y.-D.L., E.T. and C.C.
drafted the manuscript, to which R.K., D.H. and Z.L. contributed.
Y.-D.L., C.C., R.K. and E.T. interpreted data.
Competing interests. The authors declare no competing interests.
Funding. This work has been supported by the Strategic Priority
Research Program of the Chinese Academy of Sciences (grant nos.
XDB26000000, XDB18000000), the National Natural Science Foun-
dation of China (grant nos. 41672011, 41688103), and the Second
Tibetan Plateau Scientific Expedition and Research project (grant
no. 2019QZKK0706).
Acknowledgements. We are grateful to Yan Fang for technical help with
confocal imaging, Dinghua Yang for the artistic reconstruction, and
Jyrki Muona and Luiz F. L. da Silveirafor discussion on the antennal mor-
phology of Eucnemidae and Lampyridae, respectively. We also thank the
editors and three anonymous reviewers for their helpful comments.
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