Geiserocerus Roza, 2025, gen. nov.
Creators: name: Silva Roza, André
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Phengodidae
Geiserocerus

description: Geiserocerus gen. nov.
Figs 1, 2, 3, 4, 5, 6
Type species.
Geiserocerus flavifrons sp. nov., here designated.
Etymology.
The name is in honor of the entomologist Michael Geiser, a great coleopterist researcher who largely contributed to the knowledge of world beetles, with a large focus on morphology and taxonomy of soft-bodied families. Michael kindly loaned me several Phengodidae specimens from the BMNH. Singular genitive, masculine.
Diagnosis.
Antenna with 12 antennomeres, antennomeres IV – XI with two short symmetrical compressed and fusiform branches, slightly longer than respective antennomere, antennomere XII claviform (Fig. 2 I); interantennal distance close to 3 × antennal socket width (Figs 1 C, 2 D); labrum fused to frontoclypeus (Figs 1 C, 2 A); mandibles short, bent almost in a right angle near base, not projected, obliquely crossed over each other, without a notch on external margin to fit other mandible and with extra medial teeth with rhomboid apex (Fig. 2 H); maxillary palpi 4 - segmented, last segment digitiform (Fig. 2 F); labial palpi 3 - segmented (Fig. 2 G); one gular suture and posterior tentorial pit consisting of a single small fossa (Fig. 1 B); elytron around 3 × as long as wide, external margin slightly curved and convergent with the other elytron posteriorly, slightly thickened apically (Fig. 4 A); wing with radial cell open and transverse, vein r 4 interrupted, r 3 absent (Fig. 4 C); first tarsomere of pro- and mesotarsus with a ventral comb covering the entire tarsomere (Fig. 2 J); claws simple, without visible teeth (Fig. 2 J); aedeagus with paramere slightly asymmetrical, paramere apex unevenly round, toothed inward, with short and scarce bristles (Fig. 5 G – I).
Description.
Male. Head (Figs 1 C, D, 2). Head slightly wider than long, with posterior half of lateral margin sinuous, slightly convergent posteriorly, apical fourth usually covered by pronotum, slightly wider than pronotum (Figs 1 C, 2 A); antenna 1.5 × as long as head width, with 12 antennomeres, antennomeres IV – XI with two short symmetrical compressed and fusiform branches, slightly longer than respective antennomeres, antennomere XII claviform (Fig. 2 I); eyes not protruding, coarsely faceted (Fig. 1 C, D), frontoclypeus with a subtle declivity between antennae, from interantennal area up to anterior margin of labrum (Fig. 2 C), interantennal distance close to 3 × antennal socket width (Figs 1 C, 2 D); labrum fused with frontoclypeus, bilobate by a median emargination on anterior margin (Figs 1 C, 2 A); mandible short, bent almost in a right angle near base, not projected, obliquely crossed over each other, without a notch on external margin to fit other mandible and with extra medial teeth with rhomboid apex (Fig. 2 H); maxilla with palpi 4 - segmented, last palpomere digitiform, palpifer distinct, galea distinct, extremely short and free, highly setose, lacinia almost fused with stipe, highly setose, cardo semitriangular, 2 × wider than long (Fig. 2 F); labium with palpi 3 - segmented, short, not covered by mandibles, last palpomere fusiform, ligula absent, prementum quadrate, palpiger absent, mentum and submentum fused in a single piece, which is fused with head (Fig. 2 B, G); one gular suture, tentorial pit consisting of a single small fossa (Fig. 2 B).
Thorax (Figs 1 C, 3). Pronotum quadrate, slightly wider than long, anterior angles dorsally concave, rounded, lateral margins subparallel, posterior margin rounded (Fig. 3 A); hypomeron densely setose in anterior half, glabrous in posterior half, transverse in lateral view (2 × as long as high), with ventral margin straight up to middle, then oblique until posterior margin of pronotum (Fig. 3 D); prosternum 2 × as wide as its major length, narrowed parasagittally (Fig. 3 B); proendosternite elongated, about as long as distance between the apices of proendosternite arms (Fig. 3 C); mesoscutellum fused with mesoscutum, slightly concave in lateral view (Fig. 3 D, E); alinotum subquadrate, glabrous, lateral margins subparallel, posterior margin straight, scutum — prescutalplates sclerotized, extending ridges almost to posterior margin (Fig. 3 E, F); mesoventrite weakly sclerotized, blunt medially, mesepimeron fused to mesoventrite, mesanepisternum-mesepimeron suture conspicuous (Fig. 3 H); metaventrite depressed anteriorly (mesocoxal rests), discrimen distinct by basal half, lateral margins subparallel up to lateral-most part of metacoxa, then convergent posteriorly, posterior margin rounded (Fig. 3 H); mesendosternite with two parasagittal thin projections directed upwards (Fig. 3 I); metendosternite diamond-shaped, spatulate, 5 × as long as wide, median projection acute anteriad, with two small lateral laminae (Fig. 3 I); elytron wider in anterior half, slightly convergent posteriorly, subparallel, apex slightly swollen (Fig. 4 A); posterior wings with radial cell open and transversal, around 2.5 × wider than long, r 4 interrupted both in radial cell and RP, r 3 absent, RP reaching one third of MP 1 + 2 length, medial field containing five main veins: MP 3, MP 4, CuA 1, CAS and AA 4; CuA 2 absent, anal lobe well developed, AP 3 + 4 long, J absent (Fig. 4 C); legs increasing in length from pro- to metaleg, pro- and mesotarsomere I with a ventral comb covering the entire tarsomere (Fig. 3 J); tarsomere I 2 × longer than tarsomere II, tarsomeres II – IV decreasing in length, tarsomere IV in all legs of 1 / 2 length of tarsomere V, claws simple, without any visible teeth (Fig. 3 J).
Abdomen (Fig. 5). Subparallel, tergites and ventrites extremely transverse, around 3–4 × wider than long, slightly increasing in length, tergite VIII as wide as long; tergites with anterior margin deeply emarginate, lateral margins subparallel, posterior margin straight to slightly rounded (Fig. 5 A); tergite VII with a fringe of microsetae on posterior margin (Fig. 5 C); tergite IX transversal, with a membranous division in middle, anterior margin oblique inward, posterior margin innerly curved; tergite X short, conical, lateral margins subparallel (Fig. 5 E); sternites with anterior margin straight, lateral margins subparallel, posterior margin straight to slightly rounded (Fig. 5 B), sternite VIII with a membranous, densely setose projection on anterior margin (Fig. 5 D), sternite IX elongate, posterior margin slightly emarginate (Fig. 5 F); aedeagus trilobed, phallobase attached to median lobe, slightly sclerotized, and shaped as a ribbon-like stripe, median lobe cylindrical, strongly curved at base, rounded apically; flagellum encircled around median lobe at rest; about 2 × longer than median lobe length; parameres slightly asymmetrical, narrowing slightly past middle towards apex, which is unevenly round, toothed inward, with short and scarce bristles (Fig. 5 G – I).
Length. 4.55 to 5.50 mm.
Female and immature stages. Unknown.
Remarks.
Geiserocerus gen. nov. can be easily separated from most of the genera of Mastinocerinae by the presence of a ventral comb in the pro- and mesotarsomere I. When compared with other genera with the pro- and mesotarsomere I ventral combs, it can be separated from all of them, with the exception of Pseudomastinocerus Wittmer, 1963, by the medial teeth on mandible. It can be differentiated from Pseudomastinocerus by the small eyes, covering around half of head in lateral view (eyes large, covering almost the entire head in lateral view in Pseudomastinocerus), separated by more than 2 × the eye width in ventral view (separated by less than an eye width in ventral view in Pseudomastinocerus), antennomere XII claviform (cylindrical in Pseudomastinocerus) and paramere slightly asymmetrical (paramere symmetrical in Pseudomastinocerus).
description: Published as part of Silva Roza, André, 2025, A new genus and a new species of railroad-worm beetles from Bolivia (Coleoptera, Phengodidae, Mastinocerinae), pp. 203-212 in Contributions to Entomology 75 (1) on pages 203-212, DOI: 10.3897/contrib.entomol.75.e143153