Ochthebius (Gymnochthebius) falli
Creators: name: Perkins, Philip D.
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Hydraenidae
Ochthebius
Ochthebius falli

description: Ochthebius (Gymnochthebius) falli (Perkins) Species Status Reinstated
(Figs. 34–36)
Gymnochthebius falli Perkins 1980: 281
Ochthebius (Gymnochthebius) fossatus LeConte; Jäch 1994 (invalid synonymy)
The following collection/deposition data include the first records for Mexico. The data also includes several first museum depositories for the species. The new records increase the number of identified specimens in museum collections from 40 to 60. The range of this species (Fig. 36) extends northward from Oaxaca, Mexico to western Kansas and southern Idaho. The one male specimen known from the northernmost locality, Idaho, was collected in a thermal spring in 1957. The two specimens from one site in Arizona were collected in 1920. It is possible that the species has been extirpated from these localities. The records from western Texas were collected relatively recently, from 1991–2000.
New records: Mexico: Estado de México, Aguascalientes, 3–5.viii.1963, leg. P. J. Spangler (10 NMNH); km 15 Almoloya-Apán, 2.iii.1989, R. Arce col. (3 IEXA). Oaxaca, 3 km E Santiago Yolomecatl, 9.x.1990, leg. R. Baranowski (1 LUM); U.S.A.: Texas, Brewster, Big Bend National Park, Buttrill Springs, 17.vii.1991, leg. R. C. Vogtsberger (2 TAMU); Stillwell RV Park on hwy 2627, 4–5.vi.1994, leg. E. G. Riley (3 TAMU); Presidio Co., Drying Creek, 12 mi. N. Ruidosa Rd 2810, 4.v.2000, leg. G. L. Challet (1 MCZ).
Discussion. When species are placed into synonymy it is contingent upon experienced taxonomists to clearly discuss and illustrate the characters that are known to be highly diagnostic in that taxon. In Hydraenidae the male genitalia are widely known as the most highly diagnostic character to use to differentiate species. For this reason, Perkins (1980: 278) illustrated the male genitalia of representatives of all forms that were placed into synonymy, including the junior synonyms of H. (Gymnochthebius) fossatus, including examples from Brazil, Florida, Mexico, and Texas.
Contrastingly, Jäch (1994), when publishing a supposed synonymy, did not illustrate any male genitalia, and significantly did not discuss the marked differences in the male genitalia of H. (Gymnochthebius) falli and H. (Gymnochthebius) fossatus that were illustrated by Perkins (1980: 278). He also did not examine the holotype of H. (Gymnochthebius) falli. These are significant omissions.
Even though the differences in the male genitalia of the two species were illustrated adequately by line drawings in Perkins (1980), additional documentation, in the form of photographic images, is given herein, in order to make the differences abundantly clear to all students of the group.
Aedeagal characters differentiating the two species: (1) In H. (G.) falli (Fig. 34) the internal tubule is straight over the midlength, then has an abrupt bend in the distal ¼. In H. (G.) fossatus (Fig. 35) the internal tubule is arcuate for the entire length, without a bend in the distal ½. (2) The lumen aperture of H. (G.) falli has a more oval-elongate shape, whereas the aperture is as wide as long in H. (G.) fossatus. (3) The strongly sclerotized distal ends of the main-piece of H. (G.) falli are more narrowly separated than those of H. (G.) fossatus. (4) The main-piece, in dorsal or ventral views, compared to the length of the aedeagus, is wider in H. (G.) falli (l/w ca. 3.9) than in H. (G.) fossatus (l/w ca. 5.1). (5) The ratio of the width of the lumen opening and the maximum width of the main-piece is about 1: 5.5 in H. (G.) falli vs. about 1: 2.6 in H. (G.) fossatus. The shapes and sizes of these structures are all integrated by behavior: the aedeagal tube is everted during copulation (Perkins 1980: 20). These significant differences are not easily overlooked.
The specimens used to illustrate these structural differences were collected at the same locality in Mexico, during the same collecting event. Although the aedeagi used to illustrate these structures are approximately the same length, the adults differ notably in size, the specimen of H. (G.) falli being larger (1.89 vs. 1.65 mm total length). There is considerable body size variation of H. (G.) fossatus over its extensive geographical range (see Perkins 1980). Specimens of H. (G.) falli average larger than the upper end of this size variation. Another difference in the figures is that the specimen of H. (G.) fossatus is teneral. This of course has no bearing on the decision that the specimens represent two species.
description: Published as part of Perkins, Philip D., 2023, New Neotropical and Nearctic species of water beetles in the genera Hydraena Kugelann and Ochthebius Leach, a key to North American genera and subgenera of the family, new distribution records, and a synopsis of ecology, behavior and morphology related to aquatic life (Coleoptera: Hydraenidae), pp. 1-86 in Zootaxa 5367 (1) on pages 74-75, DOI: 10.11646/zootaxa.5367.1.1, http://zenodo.org/record/10145106