A new genus of railroad-worm beetles from the Atlantic Rainforest from Brazil (Coleoptera: Phengodidae, Mastinocerinae)

Here we describe a new genus, Cleidella gen. nov., and two new species, C. picea sp. nov. and C. silveirai sp. nov., all from Rio de Janeiro State, Brazil. The new genus is characterized by the interantennal distance subequal to scape length, antenna with 11 antennomeres, IV to X with two long symmetrical branches; mandibles long, projected and not crossed, pointed forward obliquely from head; maxillary palpi 4‑segmented, last segment digitiform; labial palpi 2‑segmented; posterior tentorial pit consisting of a single small fossa; elytron surpassing from the fourth to fifth abdominal segment, 3.3‑3.9× longer than wide; first tarsomere of protarsus with a ventral comb as long as the tarsomere length; wing with radial cell closed and transverse, vein r4 interrupted; aedeagus with paramere symmetrical, apex unevenly round, toothed inward, with short and scarce bristles. We provide a key to Mastinocerinae genera with 11 antennomeres, as well as illustrations for the diagnostic features for this new genus and a key to its species.

Currently, the group has three subfamilies in the Americas: Phengodinae LeConte, 1881, Mastinocerinae Leng, 1920and Penicillophorinae Paulus, 1973. No phylogenetic analysis was ever conducted in order to test the monophyly of any genus in the family, and some of them may prove not to be natural groups. The internal relation of the family is unresolved, as the subfamilies were shown to be para-or polyphyletic, presenting the need for an updated classification through future phylogenetic analyses (Zaragoza-Caballero & Zurita-García, 2015). Additionally, the Middle East Cydistinae (two genera and seven species), previously an Elateroidea incertae sedis, were recently found to be the sister group of the American Phengodidae, based on molecular data, and included in the group as a subfamily (Kundrata et al., 2019). ISSN On-Line: 1807-0205 ISSN Printed: 0031-1049ISNI: 0000-0004-0384-1825 Mastinocerinae Leng, 1920 is presently composed of 28 genera in the entire American continent (Zaragoza-Caballero & Hernández, 2014;Roza et al., 2017Roza et al., , 2018Roza & Mermudes, 2019;Vega-Badillo et al., 2020). The group is morphologically diverse and badly defined, with no genera ever revised and several new taxa waiting to be described. Inside the variation in their morphology, the genera in Mastinocerinae may present antennae with 10 antennomeres (two genera), 11 antennomeres (four genera) or 12 antennomeres (22 genera). The four genera with 11 antennomeres are: Euryognathus Wittmer, 1976, Euryopa Gorham, 1881, Steneuryopa Wittmer, 1986and Microphrixothrix Roza & Mermudes, 2019 Here, we describe a new genus, the fifth with 11 antennomeres, and two new species. One species is from the Serra dos Órgãos, on the Serra do Mar Mountain range, and the other from the previous location, and also Ilha Grande, Angra dos Reis. Both localities are in the Atlantic Rainforest of Rio de Janeiro State, Brazil. We also present a key to the genera of Mastinocerinae with 11 antennomeres, and to the species of the new genus.

Study areas
The Parque Nacional da Serra dos Órgãos (PARNASO) is located at the Serra do Mar mountain range, in the Atlantic Rainforest of Southeastern Brazil. It includes in totality an area of 20,030 ha, with altitudes from 200 to 2,263 m, nested at the borders of four municipalities in the Rio de Janeiro State: Guapimirim, Magé, Petrópolis and Teresópolis (ICMBIO, 2008). Its phytophysiognomies include: lower montane forest (below 800 m), montane forest (600 to 1,500 m), high-montane forest (1,500 to 2,000 m) and the "Campos de altitude" (CA) or "Brazilian Páramos" (starting at 2,000 m) (Rizzini, 1954;Veloso et al., 1991;Safford, 1999). Its climate varies from hot and rainy summers to humid winters, when temperatures near freezing are found at the mountaintops (Flinte et al., 2009).
The Parque Estadual da Ilha Grande (PEIG) protects an area of 12,072 ha at Ilha Grande, a continental island in the Angra dos Reis municipality, Rio de Janeiro State. The PEIG ranges elevations from sea level to 1,031 m, of which Pico da Pedra da Água (1,031 m) and Pico do Papagaio (959 m) stand out as the highest peaks. Its climate is rainy during all year, with the higher rates in the summer and lower in winter, with enough pluviosity to cause landslides on densely forested areas during summer. The park includes the following vegetation types: Dense Ombrophilous Forest, the Restinga and the Mangrove (INEA, 2010).

Collection, dissection and terminology
All specimens were collected by Malaise traps and preserved in 90% alcohol.
Specimens are deposited at Coleção Entomológica Prof. José Alfredo Pinheiro Dutra, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil (DZRJ) and Museu de Zoologia, Universidade de São Paulo, São Paulo, Brazil (MZSP). Terminology follows Costa et al. (1999), Costa & Zaragoza-Caballero (2010) and Zaragoza-Caballero & Zurita-García (2015). For hind wings, we follow Kukalová-Peck & Lawrence (1993). Specimens with the abdomen dissected have their terminalia preserved in alcohol. Photographs and measurements were taken with a Leica DFC450 and Application Suite CV3 multifocus software. The photographs were edited using Adobe Photoshop and the figure plates were designed with Adobe Illustrator (Adobe Systems). Total length was given by the sum of head, thorax and abdominal lengths, because extracting only overall body size could be misleading due to pronotal and head declination. Specimens were cleaned with ultrasonic sound for scanning electron microscopy (SEM), which was made with a Carl Zeiss, FEG Sigma 300 VP. We generated the distributional maps using the software Quantum GIS 2.14.3 (QGIS Development Team, 2016).
Female and immature stages: Unknown.
Etymology: Singular genitive, feminine. The name is in honor of the entomologist Cleide Costa, in the commemoration of her 80th birthday. Professor Costa is a great researcher who greatly contributed to the knowledge of bioluminescent beetles, including phengodids, with a large focus on morphology and natural history.
Biology and distribution: Cleidella gen. nov. is only known from the Serra dos Órgãos, from 700 to 1,800 m of altitude, and in Ilha Grande, around 700 m of altitude, both in Rio de Janeiro State, Brazil. It is known to occur from spring to summer. No live specimens were observed to date, so there is no data regarding their habits.
Remarks: There are four described genera in Mastinocerinae with 11 antennomeres: Euryognathus, distributed in Venezuela, Paraguay and Argentina, Euryopa, distributed from Guatemala to Argentina, Steneuryopa, known from Costa Rica, and Microphrixothrix, known from Brazil. Cleidella gen. nov. can be easily separated from Microphrixothrix by the interantennal distance subequal to scape length (bigger in Microphrixothrix) and  the cylindrical flabellae (lanceolated in Euryopa) and first tarsomere of protarsus with a ventral comb (the first tarsomere of pro-and mesotarsus with a ventral comb in Euryopa); and from Steneuryopa by the interantennal distance bigger than scape length (smaller in Steneuryopa), first tarsomere of protarsus with a ventral comb (without comb in Steneuryopa) and MP4 simple (bifurcated in Steneuryopa).
Key to the species of Cleidella gen. nov.

Description, male
Measurements (n = 4): Morphology: Head wider than long, integument glossy, finely punctate, interocular distance occupying slightly more than half of head width in dorsal view (Fig. 1E); eyes occupying nearly half of head width, in lateral view, posterior margin vertical, slightly reniform (Fig. 1C); antennomere IV 2× longer than III, progressively longer from IV to X, XI cylindrical, 1.5× longer than X; IV-X each with two long, symmetrical branches, 2 to 8× longer than antennomere (Fig. 1D). Pronotum 1.1× wider than long, integument glossy, finely punctate, anterior margin curved, lateral margins convergent in anterior half, dorsally parallel in posterior half, posterior margin slightly curved (Fig. 1F). Elytron heavily setigerous punctate, 3.1-3.5× longer than wide (Fig. 4A), reaching anterior margin of forth abdominal segment (Fig. 1B). Tergite IX transversal, twice wider than long in the middle line; tergite X slightly longer than wide (Fig. 5A); sternite IX twice longer than wide when including membranous area, inner curved in the posterior margin (Fig. 5B). Aedeagus: basal piece entirely sclerotized, ribbon-like; median lobe cylindrical, strongly curved at base, rounded and constricted apically, with many tiny glandular openings; flagellum encircled around median lobe at rest; about 1.5× longer than median lobe length; parameres parallel, symmetrical, narrowing slightly past the middle towards the apex, which is unciform, toothed inward, with short and scarce bristles separated by a distance at least twice the seta length (Figs. 5C-H).
Coloration: Body overall dark brown, with head and pronotum from black to dark brown, and mandibles, palpi and internal margin of pro and mesocoxae and femora brown to light brown.

Females and immatures: Unknown.
Etymology: The specific name is a Latin adjective for "pitch-black" and refers to the dark overall color of the specimens' integument.
Biology and distribution: Cleidella picea sp. nov. occurs on the Spring and Summer of the southern hemisphere. It inhabits altitudinal areas of the Serra dos Órgãos, in the Serra do Mar mountain range, around 1,250-1,800 m, in a vegetation type of montane and high-montane forest.
Remarks: This species can be easily distinguished from Cleidella silveirai sp. nov. by the eyes, in lateral view, with posterior margin vertical, slightly reniform (strongly obliquely projected in P. silveirai sp. nov.); pronotum slightly wider than long (distinctly wider than long in P. silveirai sp. nov.); and the body overall dark brown, with head and pronotum from black to dark brown, and mandibles, palpi and internal margin of pro and mesocoxae and femora brown to light brown (body overall light brown, head brown, palpi, thoracic sterna, legs, tergites and sternites pale yellow in P. silveirai sp. nov.).

Description, male
Measurements (n = 6): Morphology: Head wider than long, integument glossy, finely punctate, frons slightly concave between antennal insertions, interocular distance occupying half of head in dorsal view (Fig. 6F); eyes occupying ¾ of head width, in lateral view, posterior margin strongly obliquely projected (Fig. 6E); antennomere IV 1.5-2× longer than III, progressively longer from IV to VIII, IX and X progressively shorter, XI cylindrical, 1.5-2× longer than X; IV-X with two symmetrical branches, 2 to 4× longer than antennomere ( Fig. 6C-D). Pronotum 1.4× wider than long, integument glossy, finely punctate, anterior margin slightly curved, lateral margins weakly convergent, posterior margin slightly curved (Fig. 6F). Elytron heavily setigerous punctate, around 3.5× longer than wide (Fig. 6A Remarks: This species can be easily distinguished from Cleidella picea sp. nov. by eyes, in lateral view, strongly obliquely projected (with posterior margin vertical, slightly reniform in C. picea sp. nov.); pronotum distinctly wider than long (slightly wider than long in C. picea sp. nov.); and the body overall light brown, head brown, palpi, thoracic sterna, legs, tergites and sternites pale yellow (body overall dark brown, with head and pronotum from black to dark brown, and mandibles, palpi and internal margin of pro and mesocoxae and femora brown to light brown in C. picea sp. nov.). Two distinct populations of Cleidella silveirai sp. nov. were found, around 100 km apart from each other. The specimens from Ilha Grande have smaller flabellae in the antennae (2 to 3× the antennomere length) and the antennomere XI 1.5× the antennomere X length, while the specimens from the Serra dos Órgãos have longer flabellae in the antennae (3 to 4× the antennomere length) and the antennomere XI 2× the antennomere X length. However, as this was the only difference found between the populations, they were considered as a single species.

DISCUSSION
With a few exceptions, like in Phengodes or Zarhipis, most phengodid species have very narrow geographic ranges (Costa et al., 1999;Zaragoza-Caballero & Pérez-Hernández, 2014). Some features that might converge in explaining their restricted ranges include: soft body, apparently semelparous lifestyle (Tiemann, 1967) and poor flying ability. Together, these features render them sensitive to temperature and humidity variation at the microclimate scale, and subject to wind forces (see Viviani & Bechara, 1997;Costa & Zaragoza-Caballero, 2010). Moreover, all known phengodid females are apterous and larviform, which facilitate even more allopatric speciation events due to vicariance, a common phenomenon in beetle lineages with soft-bodies and larviform females (see Bocak et al., 2008).
The Atlantic Rainforest presents a complex system of mountain chains with altitudinal gradients of temperature, humidity, and vegetation cover. This variation from the surrounding lowlands towards mountaintops may drive local adaptation and ecological speciation, originating endemic taxa (reviewed in Hodkinson, 2005). These conditions may be especially influential on the evolutionary history and speciation of railroad-worms. This pattern of endemism has been observed in other soft-bodied elateroid beetles, such as lampyrids (e.g., Silveira et al., 2016) and phengodids (e.g., Roza et al., 2017).
The here-described new genus presents an interesting pattern of distribution, with two apparently isolat-ed populations of Cleidella silveirai sp. nov. around 100 km apart from each other. A similar pattern was found in two species of Akamboja Roza, Quintino, Mermudes & Silveira (Roza et al., 2017(Roza et al., , 2018. When compared with widespread species in other genera of Phengodidae (e.g., Zarhipis, Phrixothrix Olivier, 1909 andStenophrixothrix Wittmer, 1963), both Cleidella gen. nov. and Akamboja stand out by their very short body length (<5 mm), which could prevent long distance dispersal. This isolation, however, could be a sampling bias (Roza et al., 2018), as most of rail-road worm species have their distribution only superficially known. Nonetheless, these aforementioned species are particularly interesting for phylogeographic studies, and future studies on genetic diversity and structuring may reveal the history behind such disjunct distribution.