Ceratogeusis thamiresae Ferreira, gen. et sp. nov., the first Telegeusinae with flabellate antennae, is described from Panama. The new genus and species is diagnosed and illustrated, and an updated key for the genera of Telegeusinae is given. The Telegeusinae genus Platydrilus López-Pérez & Zaragoza-Caballero, 2021, was discovered to be a junior homonym of Platydrilus Michaelsen, 1891 (Annelida, Oligochaeta, Eudrilidae), and therefore a pre-occupied name.

Elateroidea, Neoteny, Paedomorphosis

After receiving a loan of unidentified soft-bodied beetles from Texas A&M University Insect Collection (TAMU), I noticed a small shrunken Panamanian specimen possessing flabellate antennae. At first, I thought it was a Melyridae or a Phengodidae; however, a closer examination revealed that the specimen possessed the diagnostic characters of Telegeusinae Leng, 1920 (Elateroidea, Omethidae), including the distinct pronotum submarginally impressed, the modified maxillary palps, with terminal palpomere elongate, the anterior margin of labrum shortened and transverse, bearing a pronounced median tooth, and the shortened and apically rugose elytra, leaving more than five abdominal segments exposed.

Telegeusinae is one of the subfamilies of Omethidae, a small family of soft-bodied beetles within the superfamily Elateroidea (Kundrata et al. 2014; Cai et al. 2022; Bouchard et al. 2024). Members of this subfamily are exclusively found in the New World, with a Southern Nearctic and Neotropical distribution (Miller 2002; Roza et al. 2019; Perez-Flores and Zaragoza-Caballero 2024). Telegeusinae includes five genera, and 27 described species, most of which are found in Mexico (Roza et al. 2019; Perez-Flores and Zaragoza-Caballero 2024). Members of this group are mainly and easily recognized by their modified maxillary and labial palps, with the last palpomeres elongate, multiple times longer than the sum of preceding palpomeres, especially in the genus Telegeusis Horn, 1895.

Based on the examination of a recently available TAMU specimen I describe and document for the first time the extraordinary morphology of this beetle.

The single studied specimen is deposited at TAMU. The identification and placement of the specimen in Telegeusinae was based on previous literature on the group (Ivie 2002; Miller 2002; Roza et al. 2019; Perez-Flores and Zaragoza-Caballero 2024) and comparison with museum’s specimens (Natural History Museum London; Montana Entomology Collection, Montana State University; SDEI). The holotype was studied under a Leica® S9E, with magnification up to 50×. Prior to its study, the whole specimen was relaxed in a solution of 50% water and 50% EtOH 95% overnight. It was then placed in water for 15 minutes, followed by its inclusion in a water-based intimate lubricant, where the specimen was photographed. The dissected genitalia is permanently preserved in glycerin in a microtube placed on the pin under the specimen. After all images were taken, the specimen was glued on a card.

Morphological terminology follows Lawrence et al. (2011), and to maintain consistency with the latest described genera, the general description style of Lopez-Perez and Zaragoza-Caballero (2022). Photos of specimens were taken with a Canon 6D DSLR with an MP-E 65 mm lens, and a Mitutoyo 10X Microscope Objective (M PLAN APO) attached to a Raynox DCR 150 tube lens adapter purchased from WeMacro (https://wemacro.de/). Images were stacked using Zerene Stacker^® version 1.04. Enhancements to digital images were made in Adobe Photoshop^® and Adobe Lightroom^® for iPad, and plate preparations were made in Adobe Illustrator^® CC 2024.

The antennae of insects play an important role in their lives, such as foraging, environment recognition, and sexual communication (Faucheux and Kundrata 2017). Insects which have flabellate and pectinate antennae have increased surface area and often a higher number of sensilla (Gao et al. 2016), including those associated with pheromone reception. Antennae morphology is quite variable across lineages of beetles known or suspected to be affected by the paedomorphosis syndrome (as is the case of all telegeusids, see below). In the case of beetles affected by the paedomorphosis syndrome, such as some Drilini, Lampyridae and Ripiphoridae, it is thought that sexual communication is probably based on pheromone signaling (De Cock and Matthysen 2005; Faucheux and Kundrata 2017; Batelka et al. 2021), where individuals heavily rely on their antennae for identifying a mate. In Elateroidea, for example, nearly all Phengodidae species (e.g., Roza et al. 2017; Coelho et al. 2024; Ferreira et al. 2024), many Neotropical Lycidae (Kazantsev 2013, 2017), and Drilini (Elateridae) (Kundrata and Sormova 2018; Kundrata and Packova 2024) have pectinate or flabellate antennae. However, the presence of simpler (i.e., filiform, serrate or moniliform) antennae also occurs in those very same families, e.g., Bocakova (2014), Kazantsev (2018), and Ferreira and Ivie (2022) for Lycidae; Roza et al. (2024) for Phengodidae; Kundrata et al. (2018), Hoffmanova and Kundrata (2022) for Elateridae, as well as Lampyridae (De Cock and Matthysen 2005; Ferreira et al. 2024b; Ferreira 2024; Hodson and Branham 2024).

Telegeusids are only known by males, and their females, which are suspected to be affected by the paedomorphosis syndrome and hypothesized to be larviform, remain unknown (Miller 2002; Ivie 2022). Their reproductive strategies as well as their communication mechanisms remain completely unknown. Even their morphology remains unexplored, and nothing is known about the ultrastructure and sensilla of telegeusids’ antennae and their modified palps. Some other omethids are known to have pectinate or flabellate antennae (Matheteus theveneti LeConte, 1874, Ginglymocladus Van Dyke, 1918 and Drilonius Kiesenwetter, 1874), but none of these are affected by the paedomorphosis syndrome. All described telegeusid species have filiform (Telegeusis, Pseudokarumia Wittmer, 1976, Platydrilus, and Stenodrilus), moniliform (Pseudotelegeusis jiliotupaensis Zaragoza-Caballero, 2008) or distinctly serrate (all other described Pseudotelegeusis species) antennae (Ivie 2002; Miller 2002; Roza et al. 2019; Perez-Flores and Zaragoza-Caballero 2024). Although telegeusids have simple antennae, I hypothesize that their enlarged and elongated palps may have evolved in response to their need to find larviform females. In telegeusids, it appears that the simpler (filiform) the antennae, the longer the palps (e.g., Telegeusis spp.), while taxa with modified and slightly expanded antennae (serrate or subserrate, such as in Pseudotelegeusis) have comparatively shorter and smaller palps. A closer look and investigation of telegeusids’ antennal and palps’ ultrastructure could provide insights to this hypothesis. Particularly, if there is a correlation between a higher number of sensilla (especially those associated with pheromone’s perception), and antennal and palps’ modifications of telegeusids.

I am grateful to Mario Cupello (FSCA) for loaning the material that resulted in the discovery of this new species, to Michael F. Geiser, Max Barclay (Natural History Museum, London), Michael A. Ivie (Montana Entomology Collection, Montana State University), to Felipe Francisco Barbosa (Universidade Federal do Rio de Janeiro, UFRJ) for his suggestions and corrections in an earlier version of this manuscript, to Robin Kundrata (Palacký University Olomouc) for pointing out the existence of the junior homonym of Platydrilus, to André S. Roza (UFRJ) and editor Marianna Simões for their corrections and suggestions in the submitted version of the manuscript. I want to thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) of Brazil for the novation process 202559/2015-7.