ZooKeys 1092: 63277. (2022) A peer-reviewed open-access journal

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A new species of Petalacmis firefly from Bolivia,
with a key to species (Coleoptera, Lampyridae)

Luiz E Lima da Silveira! , Marc A. Branham?

| Department of Biology, Western Carolina University, Cullowhee, NC 28723, USA 2 Department of Ento-
mology and Nematology, University of Florida, RO. Box 110620, Gainesville, FL 32611-0620, USA

Corresponding author: Luiz FE. L. da Silveira (limadasilveiral@wcu.edu)

Academic editor: V. S. Ferreira | Received 12 January 2022 | Accepted 26 February 2022 | Published 4 April 2022
http://zoobank.org/94 1 DOFO9-D7EE-4799-B875-CCF7AA27C9B4

Citation: Lima da Silveira LF, Branham MA (2022) A new species of Petalacmis firefly from Bolivia, with a key to
species (Coleoptera, Lampyridae). ZooKeys 1092: 63-77. https://doi.org/10.3897/zookeys.1092.80464

Abstract

Petalacmis Olivier, 1908 is a poorly known genus of firefly endemic to South America and is currently
the only member of the subfamily Lampyrinae, tribe Lampyrini known to occur on the continent. Here,
we describe a new species, Petalacmis triplehorni sp. nov. from Bolivia and compare it to the two other
described species in the genus. A key to Petalacmis species based on male traits, as well as illustrations of
morphological features, are given in detail for the first time. We present unique, previously neglected traits

of Petalacmis species and compare them to other Lampyrinae.

Keywords
Firefly, Lampyrini

Introduction

Petalacmis E. Olivier, 1908 is an interesting and unique genus of fireflies (Coleoptera,
Lampyridae) with distinctive antennal morphology: males have only nine antenno-
meres, the ninth very elongate and paddle-shaped. Petalacmis is poorly represented
even in large collections worldwide (LS and MB pers. obs.), and even basic aspects
of its morphology are lacking due to the rarity of specimens available for dissection.
In fact, this genus is only known from male specimens, a widespread phenomenon in

* Both authors equally contributed to the manuscript

Copyright Luiz FL. da Silveira & Marc A. Branham. This is an open access article distributed under the terms of the Creative Commons Attribution
License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source
are credited.

64 Luiz F. L. da Silveira &¢ Marc A. Branham / ZooKeys 1092: 63-77 (2022)

lampyrids (Silveira and Mermudes 2013, 2014; Ferreira et al. 2019, 2020; Bocakova
et al. 2022) and in elateroids as a whole (e.g., Bocak et al. 2016; Bifh et al. 2021).
Therefore, detailed studies on the diversity of Petalacmis species are greatly needed in
order to produce a more comprehensive understanding of the family Lampyridae, par-
ticularly in the tribe Lampyrini. Astonishingly, Petalacmis is the only known genus of
its tribe known to occur in South America, where it remains more poorly known than
its counterparts in both the Old World and North America.

Petalacmis was erected for its type species, Petalacmis praeclarus E. Olivier, 1908,
with no subfamilial placement, by Olivier (1908). In a later work, Olivier (1910)
placed the genus in the subfamily Photininae. In his 1959 work, Green moved
Petalacmis to the superfamily Lampyrinae and the tribe Lampyrini. Green’s placement
of Petalacmis was followed in McDermott’s subsequent taxonomic work on Lampyridae
(McDermott 1964) and his 1966 catalog. Phylogenetic analyses consistently placed
Petalacmis in the subfamily Lampyrinae, but its affinities remain unsteady. Phylogenetic
analyses based on morphological data recovered Petalacmis close to the Neotropical
Pleotomini Summers, 1875 (Jeng 2008), whereas molecular-based phylogenies found
it closer to part of Lamprocerini Olivier, 1907 (Martin et al. 2019). The most recent
comprehensive classification places Petalacmis in Lampyrini (Martin et al. 2019).

Petalacmis currently consists of two species: P praeclarus from Brazil, Bolivia, and
Peru, and Petalacmis wittmeri Reichardt, 1963 known only from Brazil. A third spe-
cies, Petalacmis triplehorni sp. nov. only known from Bolivia, is described here. We
provide the first identification key to Petalacmis species based on male morphology and
document the morphological features of this genus for the first time. A discussion of
Petalacmis morphology and its comparison to other Lampyrinae is presented.

Materials and methods

Specimens were both studied and imaged under dissection microscope Leica M205 C.
Digital images were obtained and stacked using the Leica Application Suite X. Speci-
mens of P praeclarus and P triplehorni sp. nov. were measured under a Leica MZ16
microscope with a calibrated eyepiece graticule, and measurements were converted
to millimeters (Table 1). A whole specimen, as well as the abdomen of a second were
soaked in KOH 10% for 24 h before dissection to digest soft tissues. ‘The classifica-
tion scheme used in this study follows Martin et al. (2019), morphological terminol-
ogy follows Silveira and Mermudes (2014), and wing venation nomenclature follows
Lawrence et al. (2021). Specimens were deposited at the following institutions: Museo
Nacional de Historia Natural, La Paz, Bolivia (ANCB; J. Tavel); Division of Plant
Industry, Florida State Collection of Arthropods, Gainesville, Florida, United States
of America (FSCA; P. Skelley); United States of America National Museum of Natural
History, Washington, DC, USA (USNM; M. Branham), University of Georgia Collec-
tion of Arthropods, Athens, Georgia, USA (UGCA; J. McHugh); Ohio State Univer-
sity, C.A. Triplehorn Insect Collection, Columbus, Ohio, USA (OSUC; L. Musetti).

New firefly with fancy antennae discovered in Bolivia 65

Table |. Comparative measurements (average, range between parentheses) between the three known spe-
cies of Petalacmis. Measurements were taken from the material examined (see above), except for those of
P. wittmeri, which were taken from Reichardt (1963).

Dimensions (mm) P. praeclarus (n = 8) P. wittmeri (n = 1) P. triplehorni (n = 15)
Total Length 9.01 (8.13—9.46) 6.8 5.34 (5.06—5.81)
Pronotal Length 2.04 (1.74—2.24) 1.5 0.99 (0.91-1.07)
Elytral Length 7.02 (6.39-7.3) 53 4.35 (4.15—-4.73)
Results
Taxonomy

Lampyridae: Lampyrinae: Lampyrini

Petalacmis triplehorni Silveira & Branham, sp. nov.
http://zoobank.org/2F8 DCDAF-6A3 1-48BE-B757-74A9 1AFCDA37
Figs 1-4; Suppl. material 1: Fig. S1

Diagnosis. The three species of Petalacmis are easily diagnosable by size (Table 1), along
with the morphology of antennae, elytra, and pygidium (see key below). Petalacmis
triplehorni sp. nov. can be identified by the following combination of characters:
antennomeres V and VII slightly longer and wider than adjacent antennomeres
(Fig. 2H—I), elytron subparallel-sided (Fig. 3L), pygidium with sides divergent to basal
third, then convergent apically with almost straight margins, posterior margin slightly
bisinuose, lateral thirds subequal to or slightly longer than median third (Fig. 4A, C).
Measurements are given in Table 1.

Description of male. Color pattern: overall brown, except for the dark brown pro-
notal disc, translucent parasagittal rounded spots on pronotal expansions, and translucent

sterna VI—-VIII (Fig. 1); pronotal expansions often light brown (Suppl. material 1: Fig. $1).

Figure |. Habiti of Petalacmis species A, B P triplehorni sp. nov., holotype (male, prior to dissection),
habitus A dorsal B ventral B, C P praeclarus (male, from Piracicaba, Sao Paulo) B dorsal C ventral
E, F P wittmeri holotype (male), habitus E dorsal F ventral. Scale bars: 1 mm (A-D).

66 Luiz FE. L. da Silveira & Marc A. Branham / ZooKeys 1092: 63-77 (2022)

Figure 2. Petalacmis triplehorni sp. nov., male head A=F core head A dorsal B ventral/occipital C frontal
D lateral E posterior H, I antenna H lateral I frontal. Scale bars: 250 um (A=E); 500 um (H, I).

Head: head capsule about 1/3x wider than long, posterior margin almost straight,
except for the dorsal margin of occiput, which is rounded (see dorsal view, Fig. 2A),
slightly taller than long (Fig. 2D), vertex slightly depressed between the eyes (Fig. 2E).
Frons slightly intumescent (Fig. 2D), antennal sockets elliptical, 2x taller than wide,
obliquely disposed, as wide as 1/3 eye; antennifer process barely visible (Fig. 2C).
Eye as wide as 1/3 head width in dorsal view (Fig. 2A), 2/5 in ventral view (Fig. 2B),
dorsal margin emarginated inwards (Fig. 2A), frontal inner margin rounded, strongly
convergent ventrally (Fig. 2B), almost occupying the whole head capsule in lateral
view (Fig. 2D), indented posteriorly (Fig. 2B, D). Antenna with nine antennomeres
(Fig. 2H, I); scape slightly longer than wide, basally constricted; pedicel basally con-
stricted, slightly wider than long, 1/2 as long as scape; antennomeres III—VIII trans-
verse, progressively compressed, with decumbent bristles, subequal in length, except
for V and VU, which are slightly longer and wider than neighboring antennomeres, IX

New firefly with fancy antennae discovered in Bolivia 67

petal-shaped, lateral margins asymmetrical (Fig. 2H); frontoclypeus strongly depressed
between antennal sockets and labrum (Fig. 2C). Labrum (Fig. 2A—C) subcircular,
slightly acuminate anteriorly, connate to frontoclypeus, slightly wider than antennal
socket. Mandibles short (as long as labrum), slightly curved, apically obtuse, homoge-
neously bristled (Fig. 2A, D). Maxilla (Fig. 2B, C) with cardo well sclerotized, rectan-
gular; stipes oblong, subtriangular in ventral view, internal margin slightly curved, pos-
terior margins rounded, palp with 4 palpomeres; H—IV subcylindrical and transverse,
II longer than I and as long as palpifer, I as long as III, HI transverse; IV lanceolate, 3x
longer than III, with apical margin covered with bristles. Labium (Fig. 2B) with men-
tum membranous and barely distinct, divided sagittally forming two plates, each plate
elongate; submentum membranous and indistinct; palp with 2 distinct palpomeres,
apical palpomere obconical. Gula coriaceous, as long as wide, paired tentorial pits
conspicuous. Occiput subtriangular, maximum width slightly over 1/2 head width,
anterior margin slightly sinuose (Fig. 2E).

Thorax: pronotum with anterior margin slightly sinuose and acuminate anteriorly
(Fig. 3A), lateral margins slightly rounded to subparallel, posterior angles somewhat
acute but not pointed, posterior margin almost straight, slightly rounded by the disc;
disc subquadrate (Fig. 3A), slightly depressed by posterior half (in lateral view, Fig.
3E), regularly punctured, punctures small and bristled, evenly spaced about 2x punc-
ture size; without a distinct line of deeper marginal punctures; pronotal expansions
well developed, anterior expansion convex in lateral view (Fig. 3C, E), maximal length
almost as long as disc (Fig. 3A); posterior margin about as wide as distance between
elytral humeri (Fig. 1A); lateral expansions bent upwards in posterior view (Fig. 3D).
Hypomeron slightly over 2x longer than tall, with a well-delimited posterior angle
(Fig. 3E). Prosternum smallest length about 10x as wide as its greatest length (Fig. 3B).
Proendosternite apically acute, widely divergent, as long as core prosternum smallest
length (Fig. 3D). Mesoscutellum very short (Fig. 3F), with posterior margin pointed,
normally at a lower level than elytra (Fig. 1A). Elytron (Fig. 3L, M) subparallel-sided,
almost 5x longer than wide, pubescent, secondary pubescence absent, with shallow
irregular punctures, texturized, with evanescent 4 costae, marginal costa narrow, epi-
pleuron reaching basal 4. Hind wing well developed (Fig. 3N), posterior margin with
anal embayment (sensu Lawrence et al. 2021), slightly less than 2x wider than long, r4
3x longer than r3, radial cell 3x wider than long, distant from anterior margin more
than the caliper of RA, costal row of setae conspicuous (Fig. 3N); CuA1 cross vein
evanescent, CuA3+4 cross vein absent; radial cell, r3 and r4 evanescent, veins posterior
to MP progressively evanescent from apex to base.

Alinotum overall weakly sclerotized, slightly wider than long (Fig. 3G), lateral mar-
gins convergent posteriorly, posterior margin slightly emarginate; prescutum extending
up to half metascutum length; without a distinct rounded area, scutum-prescutal plates
distinct and extending ridges to half alinotum length; metascutellum glabrous, with
lateral margins subparallel-sided, scutum-scutellar ridge strongly divergent posteriorly.
Mesosternum weakly sclerotized, posterior margin medially rounded (Fig. 3H). Mesos-
ternum-mesepisternum suture barely visible (Fig. 3H). Mesepisternum-mesepimeron

68 Luiz F. L. da Silveira 8&¢ Marc A. Branham / ZooKeys 1092: 63-77 (2022)

suture conspicuous (Fig. 3H). Mesepimeron-metasternum suture coriaceous (Fig. 3H,
I). Metasternum strongly depressed by mesocoxae, without a distinct anterior medial
keel, discrimen reaching basal 1/3 of metasternum length, lateral margins divergent
posteriorly up to outermost part of metacoxa, then convergent posteriorly, posterior
margin bisinuose (Fig. 3H—I). Metepisternum almost 3x longer than tall Fig. (3K).
Profemur about as long as protibia; meso and metatibia of about the same length and
slightly longer than protibia (Fig. 3O). All legs lacking tibial spurs, with tarsomeres
progressively shorter up to IV, which is bilobated, lobes reaching ¥2 V length, V slight-
ly shorter than I, and with simple, untoothed claws (Fig. 30, P). Mesendosternum
with 2 parasagittal projections slightly directed outwards, irregularly alate (Fig. 3I-K).

Figure 3. Petalacmis triplehorni sp. nov., male thorax. A—E prothorax: A dorsal B ventral C anterior
D posterior E lateral. F-K pterothorax: F mesoscutellum, dorsal G alinotum, dorsal H pterothorax,
ventral I pterothorax, dorsal (detail of meso and metaendosterna J alinotum, dorsal K pterothorax and
abdominal tergum I, lateral L-N wings: L elytron, dorsal M elytron, lateral (outer view) N left wing,
dorsal O, P legs: O left pro, meso and metaleg (left to right) P detail of left pro, meso and metaleg apices
(left to right). Scale bars: 500 um (A=K); 1 mm L=N; 750 um (O); 250 um (P).

New firefly with fancy antennae discovered in Bolivia 69

Metendosternum spatulate, roughly rhomboid (about as long as wide, with 2 acute
lateral laminae), anteriorly indented (Fig. 31).

Abdomen: tergum I with laterotergite membranous, roughly triangular, almost
indistinct (Fig. 3K); spiracle elliptical, obliquely attached to thorax (Fig. 3G, K).
Posterior corners of terga I-HI almost right-angled, IV slightly projected, V—VII
rounded and progressively projected and acute (Fig. 4A—C). Sterna H-IX visible
(Figs 1B, 4C), V distinctly more sclerotized than neighboring sterna, VI and VII with
well-developed, transverse light organs, almost as long and wide as sterna (Fig. 4B,
C, Suppl. material 1: Fig. $1). Spiracles ventral, at mid-length (Fig. 4B, C). Sternum
VIII with posterior margin slightly emarginate (Fig. 4B, C). Pygidium with anterior
margin strongly emarginate, lateral margins almost straight and convergent poste-
riorly, posterior margin bisinuate, lateral thirds subequal to or slightly longer than
median third (Fig. 4C). Syntergite membranous, as long as 4/5 sternum IX length,
widely connate to sternum IX, without distinct sutures, posteriorly bristled, anterior
margin slightly emarginate (Fig. 4D—F). Sternum IX symmetric, medially divided
by a membranous line, anterior margin rounded, lateral margins strongly conver-
gent anteriorly (Fig. 4D—F). Aedeagus overall well sclerotized (Fig. 4G—J). Phallus
(Fig. 4G-I) with a well-sclerotized dorsal plate, ventral plate indistinct; dorsal plate
basally connate to parameres, curved dorsally, apically truncate, deeply excavate ven-
trally (Fig. 4G), without apical lobes or arrow-shaped structures. Parameres ventrally
projected basally, projection somewhat rounded; reaching the dorsal plate of phallus
length, with typical lampyrine inner lobes but coriaceous; with an apical pointed

projection, which is membranous.
Female and immature stages. Unknown.

Figure 4. Petalacmis triplehorni sp. nov., male abdomen A=C core abdomen (segments [V—VIII)
A dorsal B lateral C ventral D-F aedeagal sheath D dorsal E lateral F ventral G-J aedeagus (distal tips
oriented toward top of the figure) G apical/posterior H dorsal I lateral, J ventral. Scale bars: 500 um
(A-C); 250 um (D-H).

70 Luiz FE. L. da Silveira & Marc A. Branham / ZooKeys 1092: 63-77 (2022)

Etymology. ‘This species is named for Dr Charles “Chuck” Triplehorn, Professor
Emeritus of the Ohio State University, who collected the first specimens of Petalacmis
praeclarus that one of us (MAB) first encountered as a graduate student while investi-
gating the systematics of the family Lampyridae. Dr Triplehorn has been both a men-
tor and an inspiration to MAB. It is with great appreciation and respect for Dr Triple-
horn that we name this species after him.

Material examined. Holotype, male. Boxtvia: Santa Cruz, Potrerillo del Guenda
Reserve, 1322’ elev., 17°40.262'S, 63°27.445'W, at light, J. McHugh lab exped. leg.,
6—12-I-2005 (ANCB).

Paratypes (n = 14). Botrvia ¢ Santa Cruz, Potrerillo del Guenda Reserve.; 1322’
elev.; 17°40.262'S, 63°27.445'W; at light; J. McHugh lab exped. leg.; 6—12-I-2005
(1 6, USNM) « Santa Cruz, 3.7 km SSE of Buena Vista, Hotel Flora and Fauna;
405 m elev.; 5—15-XI-2001; 17°29.949'S, 63°33.152'W; M.C. Thomas & B.K. Dozier
leg.; tropical transition forest (3 6, FSCA) * idem. (2 3, ANCB); Santa Cruz, 3.7 km
SSE of Buena Vista, Hotel Flora and Fauna; 405 m elev.; 5—15-XI-2001, 17°29.949'S,
63°33.152'W; M.C. Thomas & B.K. Dozier leg.; tropical transition forest (1 <,
OSUC) ¢ Santa Cruz, 3.7 km SSE of Buena Vista, Hotel Flora and Fauna; 405 m elev.;
5—15-XI-2001; 17°29.949'S, 63°33.152'W; M.C. Thomas & B.K. Dozier leg.; tropi-
cal transition forest, blacklight trap (2 3, UGCA) ¢ Santa Cruz, 3.7 km SSE of Buena
Vista, Hotel Flora and Fauna; 430 m elev.; 2—13-HI-2000; M.C. Thomas leg.; tropical
transition forest (3 4, ANCB) ¢ Santa Cruz, 3.7 km SSE of Buena Vista, Hotel Flora
and Fauna; 430 m elev.; 14—19-X-2000; M.C. Thomas leg.; tropical transition forest
(1 3, ANCB) ¢ Santa Cruz, 40 km NW of Potrerillo del Guenda; 400 m elev.; Gino
Nearns leg., 17-XII-2004 (1 male, USNM).

Key to the species of Petalacmis

1 Elytron subparallel-sided, slightly tapering distally (Fig. LA—D)........ 2
= Elytrarelliptical; widest in: middle (Figs WE FE). sci smcegiactdauancsseeeatea pleas.
ph se anisbctrunel tal nua tipssla Meat reauakhs mehpebasteans uated Petalacmis wittmeri Reichardt
2 (1). Antennomeres V and VII as wide as VI and VII, apical antennomere
nearly 2x longer than remaining antennomeres together (Fig. 5A); elytral
outer expansion (also known as explanate margin) extending up to 2/3 of
elytral length, yellowish (Fig. 3C, D); pygidium with sides rounded, posterior
margin strongly bisinuose, slightly longer at median 1/3 wee eects
CRNA ac Ahn ote Bate silage tae on ae Petalacmis praeclarus E. Olivier
-- Antennomeres V and VII slightly longer and wider than neighbor antenno-
meres, apical antennomere as long as the remaining antennomeres together
(Fig. 2H, I); elytral outer expansion feebly developed throughout, and of the
same color as the rest of the elytron (brown) or slightly brighter (Figs 1A, B,
3L; Suppl. material 1: Fig. S1A); pygidium with sides almost straight, pos-
terior margin slightly bisinuose, lateral thirds subequal to or slightly longer
than median 1/3 (Fig. 4A—C) wee Petalacmis triplehorni sp. nov.

New firefly with fancy antennae discovered in Bolivia Fell

Figure 5. Comparison between the antennal morphologies A Petalacmis praeclarus B P wittmeri
C P triplehorni sp. nov. Scale bar: 1.0 mm.

Petalacmis praeclarus Olivier, 1908

Material examined. Brazit: Minas Gerais, Lambari [spelled Lambary], X1.1924, J.
Halik col. (1 male, USNM 3083) // Brazil Halik 1966 coll.; same data, XI.1924 (1
male, USNM 3084); same data, XI.1924 (1 male, USNM 3085); Sao Paulo, Sao Pau-
lo, Santana [spelled St. Anna, Cap. S. Paulo], XII.1934, J. Halik col. (1 male, USNM
5047).] // Brazil Halik 1966 coll. collection; Sao Paulo, Cantareira, 23.VII.1933, J.
Halik col. (1 male, USNM 2208) // Brazil Halik 1966 coll. collection; S40 Paulo,
Botanical garden [spelled orto flor], XII.1921, J. Halik col. (1 male, USNM 7190) //
Brazil Halik 1966 coll. collection; Sao Paulo, Piracicaba, 6.X.1965, Blacklight, C. A.
Triplehorn col. (2 males, M. Branham collection).

Discussion

Distribution of Petalacmis spp.

To date, all Petalacmis species are known from lowland localities across South America
east of the Andes. Petalacmis praeclarus was described from “Brazil”. It has since been

72 Luiz FL. da Silveira & Marc A. Branham / ZooKeys 1092: 63-77 (2022)

collected in Bolivia and Peru (Olivier 1908; Reichardt 1963; McDermott 1964, 1966;
Lawrence et al. 2001) and the Atlantic Rainforest in Brazil (see Material examined
above). Such a widespread distribution is uncommon in Neotropical fireflies, and the
existence of overlooked or cryptic species should be considered in future comprehen-
sive taxonomic reviews. In 1963, Reichardt described the second species, P wittmeri
which was collected Ananindeua, in Para state, Brazil. Petalacmis triplehorni sp. nov.
was collected near Buena Vista, Santa Cruz, Bolivia. Due to its small size and nocturnal
habit, the genus is likely to have been overlooked, particularly in South America, where
taxonomic expertise in fireflies was largely lacking until fairly recently.

Thoughts on the mating system of Petalacmis species

Due to the presence of large eyes and photic organs in the male, one might expect
that both the male and female of these species are luminous and use luminous signals
for pair-formation, as seen in several firefly subfamilies (Branham and Wenzel 2003;
Branham 2010; Stanger-Hall et al. 2018). The fact that no females are currently known
for any of the three species in this genus may suggest that females are sedentary, perhaps
brachypterous or even apterous, as seen in other lampyrids (e.g., Faust 2017; Stanger-
Hall et al. 2018). Alternatively, these species may be so uncommonly encountered that
no females have been collected.

Morphology and systematics of Petalacmis

The affinities of Petalacmis have been investigated in two comprehensive phylogenies of
Lampyridae. Based on morphological data, Jeng (2008) found Neotropical Pletomini
Summers, 1875 (i.e., Calyptocephalus Gray, 1832, Phaenolis Gorham, 1880, Ophoelis
Olivier, 1911, and Roleta McDermott, 1962) sister to Petalacmis. On the other hand,
the molecular-based phylogeny by Martin et al (2019) found Petalacmis sister to Lucio
Laporte, 1833 and Lamprocera Laporte, 1833, both in the Lamprocerini Olivier, 1907.
Neither phylogenetic hypothesis found evidence of exclusive shared ancestry with the
Lampyrini, where they are currently placed (Martin et al. 2019). However, the taxa
which were more closely associated with Petalacmis by Jeng (2008) were not included
in Martin et al. (2019); hence, the sister-lineage of Petalacmis remains unclear.

As our study was the first to thoroughly survey the anatomy of Petalacmis, we
provide some comparisons to inform the ongoing debate on the phylogenetic afhnities
of this genus. We assume that our description of P triplehorni sp. nov. includes traits
that are likely to be shared with other species in the genus, or even traits common to
all of them. In addition to the very distinctive “petal-like” antennal morphology, we
observed previously obscured traits of Petalacmis that differ significantly from those of
other lampyrine genera. For example, Petalacmis is unique among lampyrine genera in
having (i) an intumescent and laterally keeled frons (Fig. 2A, D), (ii) mandibles short
apically rounded (i.e., obtuse, not pointed) frons (Fig. 2A, C—D), and (iii) a dorsal
plate of the phallus much shorter than the phallobase and strongly bent dorsally (in

New firefly with fancy antennae discovered in Bolivia 72

ventral view), with sides parallel and straight in apical view, deeply grooved (in apical/
posterior view), and apically truncate (Fig. 4H-J). Other genera of Lampyrini often
have frons that are not intumescent (e.g., flat or depressed between antennal sockets),
mandibles apically very acute (i.e., needle-like), and phalli at least slightly longer than
phallobase, sinuose or almost straight (but never strongly bent dorsally), with sides
sinuose, and apex variably acute, often with arrow-shaped apices (e.g., Green 1959;
Geisthardt 1986; Kazantsev 2010; Constantin 2014). Interestingly, the intumescent
frons seen in Petalacmis is known in at least some Pleotomini (e.g., Roleta; Jeng et al.
2006), and in the amydetine taxa Magnoculus and Memoan (Silveira and Mermudes
2013; Campello-Gongalves et al. in press).

Another trait shared with all three amydetine genera (Amydetes Illiger, 1807,
Magnoculus McDermott, 1964, Memoan Silveira & Mermudes, 2013; Campello-
Gongalves et al. in press), as well as many other glowing firefly taxa (Phausis LeConte,
1851, Lamprohiza Motschulsky, 1853) is the more sclerotized and slightly emarginated
sternum V (Fig. 4C), which precedes the lanterns. Another feature of P triplehorni
sp. nov. that catches the eye is the shape of abdominal sternum IX (Fig. 4F), which is
medially divided bya membranous line—a typical trait of the Lampyrini (e.g., Kazantsev
2010) that is also commonly observed across Lamprocerini and Cratomorphini (e.g.,
Campos et al. 2018; Silveira et al. 2019; Lima et al. 2021), but seldom seen in Photinini
(e.g., Silveira et al. 2022).

Concerning aedeagal morphology, lampyrine taxa very often have parameres with
an elongate, membranous apex—a trait also commonly found across Lamprocerini
and Cratomorphini (e.g., Campos et al. 2018; Silveira et al. 2019). The same membra-
nous apex is found on the aedeagus of P triplehorni sp. nov., but in a rudimentary form
(Fig. 4). The typical inner lobe of parameres (as seen for example in Lampyris (e.g.,
Geisthardt 1986; Kazantsev 2010; Constantin 2014) is also present in P triplehorni
sp. nov., although distinctly thinner and less sclerotized.

Recently, it has become more common that taxonomic studies report detailed exo-
and endoskeletal traits of the thorax, like the shape of meso and metatergal ridges, as
well as those of the endosternites. Currently, no such information is available for any
taxa of Lampyrini, which hampers any comparison. Nevertheless, we observed some
interesting traits in Petalacmis triplehorni sp. nov. and compare it to known lampyrine
taxa. For instance, the mesoscutellum of P triplehorni sp. nov. is so reduced that it is al-
most triangular, despite the median pointed projection at the posterior margin (Fig. 3F).
To our knowledge, no such rudimentary shape has been observed before in any other
lampyrid. Moreover, no other Lampyrini is known to possess an extremely reduced and
posteriorly pointed mesoscutellum. However, we observed a rather pointed mesoscutel-
lum in the lamprocerine genus Téenaspis (e.g., T. angularis, T; sinuosa; LFLS pers. obs.).

The alinotum of P triplehorni sp. nov. is clearly distinct, with a scutum—prescutal
ridge that extends to less than half the length of the metanotum (Fig. 3G), otherwise
reaching or almost so the posterior margin in most other lampyrids, where known
(e.g., Silveira et al. 2019). Such a short scutum—prescutal ridge is only known in the
distantly related Amydetinae (Silveira and Mermudes 2014; Campello-Gongalves et al.

74 Luiz F. L. da Silveira &¢ Marc A. Branham / ZooKeys 1092: 63-77 (2022)

in press). The function of that modified alinotum in Lampyridae remains unknown,
but it likely reflects changes in the flight muscles that attach to these ridges, and possi-
bly associated with changes in flight pattern. The metascutelum of P triplehorni sp. nov.
has rather oblique anterior ridges (about 45° to the lateral ridges), otherwise almost
transverse as found in most other lampyrids (e.g., Silveira et al. 2019). It is also note-
worthy that P triplehorni sp. nov. has a metaendosternum with anterior margin wide
and emarginate (a trait so far only observed in Cratomorphini; Campos et al. 2018).

Petalacmis shares with Lampyrini, Pletomonini, and Lamprocerini, the ventral po-
sition of abdominal spiracles, as well as the reduced mandibles. However, this genus
lacks key traits of all these three tribes. For example: both Lucio and Lamprocera, the
taxa placed close to Petalacmis in Martin et al.’s (2019) phylogenetic analysis, have
biflabellated antennae, elytra broadly expanded laterally and bent ventrally, and a
transverse pygidium. In contrast, Petalacmis has a petal-shaped antenna, elytra feebly
expanded and almost flat in lateral view (not bent ventrally), and a pygidium much
longer than wide. Petalacmis also lacks the typical biflabellate antennae, and the bilo-
bate sternum VIII, of the Neotropical Pleotomini. Yet, Petalacmis and the Neotropical
Pleotomini share an intumescent frons, and an elongate pygidium. Lampyrini taxa
usually have a transverse pygidium (elongate in Petalacmis), and their parameres have a
well-developed apical membranous projection (e.g., Geisthardt 1986; Kazantsev 2010;
Constantin 2014), which is at best rudimentary in Petalacmis. Therefore, the unique
combination of characters seen in Petalacmis makes its taxonomic placement within
the family Lampyridae challenging. A well-substantiated tribal placement of Petalacmis
in Lampyrinae would benefit from its inclusion in future phylogenetic analyses with
expanded taxon sampling across the Lampyridae.

Taken together, these observations highlight the potential value of traits typically
neglected in lampyrid taxonomy, and invite future anatomical studies concerning the
Lampyrinae, particularly the Lampyrini. We hope that our study fosters a future com-
prehensive review of this interesting firefly genus.

Acknowledgements

We thank Charles Triplehorn for collecting the specimens that made MAB aware of
this genus and for being a great friend and mentor, Cleide Costa for comparing the new
species to the holotype of Petalacmis wittmeri, Michael Thomas for collecting the series
of specimens described in this manuscript and making them available for study, James
E. Lloyd and Paul “Skip” Choate for commenting on an early draft of the manuscript,
Vinicius S. Ferreira and Francisco Eriberto Nascimento for the pictures of P wittmeri
(Fig. 1E, F), and Ale Maruniak for help translating Spanish. Specimens included in
this contribution were studied under or digitized at Western Carolina University, with
equipment funded by NSF#2001683 CSBR: Natural History: Development of the
Catamount Biological Collections to Enhance Biodiversity Research and Education in

Southern Appalachia and NSF DEB-1655936 awarded to the University of Florida.

New firefly with fancy antennae discovered in Bolivia em)

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Supplementary material |

Figure S1

Authors: Luiz F. L. da Silveira, Marc A. Branham

Data type: Figure

Explanation note: Petalacmis triplehorni sp. nov. habitus of one of the paratypes (note
lantern morphology and the brighter pronotal expansions) A dorsal B ventral.

Copyright notice: This dataset is made available under the Open Database License
(http://opendatacommons.org/licenses/odbl/1.0/). The Open Database License
(ODDbL) is a license agreement intended to allow users to freely share, modify, and
use this Dataset while maintaining this same freedom for others, provided that the
original source and author(s) are credited.

Link: https://doi.org/10.3897/zookeys.1092.80464.suppl1