Eurhopalothrix oxente

Eurhopalothrix oxente
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Family:	Formicidae
Subfamily:	Myrmicinae
Tribe:	Attini
Genus:	Eurhopalothrix
Species:	E. oxente
Binomial name
Eurhopalothrix oxente Celante & Celante, 2024

The species was found in a small fragment (70 m x 70 m) of riparian forest dominated by Inga vera Willd. subsp. affinis (DC.) T.D. Penn (Fabales: Fabaceae: Mimosoideae). Relatively thick layers of litter accumulate below the canopy of these trees, with some points exceeding 30 cm in thickness (Fig. 3). The specimens were collected in sifted litter and rotten wood samples from the forest floor. The riparian forest fragment is located on the left bank of the São Francisco River, in the Sub-middle São Francisco hydrographic region, northeastern Brazil, in the ‘Depressão Sertaneja Meridional’ ecoregion of the Caatinga Domain (Velloso et al. 2002). The climate of the region is classified as hot semi-arid (‘BSh’ type in the Köppen climate classification), with a maximum temperature of 33 °C and a minimum of 20 °C; average compensated temperature between 24.8 °C and 28.1 °C; the highest rainfall rates are found in the months of January, February, and March; average annual rainfall between 354.0 mm and 559.2 mm during ‘usual years’, but with the possibility of ranging from 150 mm to above 800 mm (Pimentel & Assis 2022); and average monthly evapotranspiration ranging from 172.83 mm (June) to 288.69 mm (October) (Silva et al. 2015). Up until now, Eurhopalothrix oxente has not yet been found in collections carried out in the same municipality outside this riparian forest and in neighboring regions, on both sides of the river, in either shrub or arboreal Caatinga areas, and is only known in its type locality (Fig. 4).

Photo Gallery

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  Celante et al. (2024), Figure 1. Holotype of Eurhopalothrix oxente. A. Lateral view. B. Dorsal view. C. Head in frontal view. Scale bar: A = 0.5 mm; B and C = 0.2 mm. / Figura 1. Holotipo de Eurhopalothrix oxente. A. Vista lateral. B. Vista dorsal. C. Cabeza en vista frontal. Barra de escala: A = 0,5 mm; B y C = 0,2 mm.
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  Celante et al. (2024), Figure 3. Photo in the riparian forest where Eurhopalothrix oxente was collected, on the left bank of the São Francisco River in Petrolina, Pernambuco, Brazil. / Figura 3. Foto en el bosque ribereño donde Eurhopalothrix oxente fue recolectada, en la margen izquierda del río São Francisco en Petrolina, Pernambuco, Brasil.

Identification

Hairs squamate, uniform, obovate, and subappressed covering the dorsal surface of the body, scape, and legs; head wider than longer; mandibles triangular, with nine teeth of varied sizes, the fourth tooth notably longer than the others, and the proximal teeth curved towards the clypeus; clypeus with anterior margin relatively straight; eyes extremely reduced.

Even with some uncertainty regarding the classification at the genus level, Eurhopalothrix oxente can be easily differentiated from species attributed to the genera Basiceros, Octostruma, and Protalaridris for having only seven antennal segments (12, 8, and 9 in the cited genera, respectively), and from the genera Rhopalothrix and Talaridris, which also have only seven antennal segments, for having relatively short, triangular and serially dentate mandibles that close tightly against the clypeal margin and against each other.

Within the genus Eurhopalothrix, the representatives of the bruchi group, to which this species was attributed, can be differentiated from the other groups of species for having the dorsal surface of the body virtually fully covered by squamate setae and the absence of differentiated setae. Eurhopalothrix oxente stands out within the bruchi group by the fourth tooth being much longer and tapered than the other ones in the mandible, whereas Eurhopalothrix bruchi has undifferentiated teeth.

Celante et al. (2024), Table 1. Definition of Eurhopalothrix oxente based on workers compared to E. bruchi. / Tabla 1. Definición de Eurhopalothrix oxente basado en obreras en comparación con E. bruchi.

Taxon	Eurhopalothrix oxente (Fig. 1)	Eurhopalothrix bruchi (Fig. 2)
Total length	2.22 - 2.32 mm	1.8 - 2.0 mm1,2
Head	Wider than longer in full face view (CI 112 - 118); posterior margin concave	In full face view, slightly longer than wider (CI 92 - 96)1,2; posterior margin slightly concave1
Eyes	Extremely reduced	Small2 and depigmented1
Clypeus	Convex posteriorly and anterior margin relatively straight, slightly concave; lateral margins clearly surpass the width of the frontal lobes	Convex posteriorly and anterior margin concave; lateral margins approximately of the same width as the frontal lobes
Surface of the mandibles	Punctate and opaque	Smooth and shiny2
Mandibles	Nine teeth of irregular size and shape, the fourth tooth much longer and tapered, posterior teeth curved towards the clypeus	masticatory margin concave, with about 10 spiniform, very thin teeth1
Promesonotum	Dorsal region flat in lateral view; slightly wider than longer in dorsal view	Almost flat2; in dorsal view, slightly longer than wider1
Propodeum	Short; concave postero-anteriorly; in lateral view, margins of the propodeum slope show well-defined lamellae forming an angle in the region close to the dorsum	Short; concave postero-anteriorly; in lateral view, uniformly rounded with a thin carina that tapers from the base towards the back1,2
Cuticle	Head, mesosoma, petiole, postpetiole, gaster, and legs densely punctate	Body densely and finely granulose-punctulate, opaque, except for the smooth and shiny mandibles2
Pilosity	Dorsal and ventral surface of the head, legs, gaster, and dorsal surface of the scape, mesosoma, petiole, and post-petiole covered by curved, obovate hairs over the body	Dorsal surfaces of the body, legs, and scapes covered with numerous short, inverted spoon-shaped hairs that appear as small, widely spaced, semitransparent scales2
1Santschi (1922); 2Brown & Kempf (1960)

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  Celante et al. (2024), Figure 2. Syntype of Eurhopalothrix bruchi. A. Lateral view. B. Dorsal view. C. Head in frontal view. Scale bar: 0.5 mm. / Figura 2. Sintipo de Eurhopalothrix bruchi. A. Vista lateral. B. Vista dorsal. C. Cabeza en vista frontal. Barra de escala: 0,5 mm.

Keys including this Species

• Key to New World Eurhopalothrix
• Key to the southern South American Eurhopalothrix

Distribution

Eurhopalothrix oxente is only known in its type locality.

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  Celante et al. (2024), Figure 4. Map of part of South America with the distribution of Eurhopalothrix oxente, and of some other specimens of the bruchi group (Caatinga limits modified from Lima 2021). / Figura 4. Mapa de parte de Sudamérica con la distribución de Eurhopalothrix oxente, y de algunos otros especímenes del grupo bruchi (límites de Caatinga de Lima 2021).

Latitudinal Distribution Pattern

Latitudinal Range: -9.36° to -9.36°.

North Temperate	North Subtropical	Tropical	South Subtropical	South Temperate

• Source: Celante et al., 2024

Distribution based on Regional Taxon Lists

Neotropical Region: Brazil (type locality).

Distribution based on AntMaps

Distribution based on AntWeb specimens

Check data from AntWeb

Countries Occupied

Number of countries occupied by this species based on AntWiki Regional Taxon Lists. In general, fewer countries occupied indicates a narrower range, while more countries indicates a more widespread species.

Estimated Abundance

Relative abundance based on number of AntMaps records per species (this species within the purple bar). Fewer records (to the left) indicates a less abundant/encountered species while more records (to the right) indicates more abundant/encountered species.

Biology

Explore Overview of Eurhopalothrix biology  Little is known about the biology of most species in this genus. Nests are rarely found, and queens and males have not been collected for many species. Longino (2013) summarized their biology "Eurhopalothrix specimens are encountered almost exclusively in samples from mass extraction techniques that recover small arthropods in sifted litter, rotten wood, and soil. Densities, at least in the northern Neotropics, are usually low, with workers occurring in < 10% of quantitative samples of 1 m2 litter plots, but occasionally may reach densities as high as 40% of samples. Live colonies of Old World Eurhopalothrix were observed by Wilson (1956) and Wilson and Brown (1984), and a Costa Rican colony of Basiceros manni was observed by Wilson and Hölldobler (1986). All basicerotines, including Eurhopalothrix, are thought to be predators in tropical leaf litter, relying on stealth or sit-and-wait techniques. Sampled specimens are often coated with a thin layer of clay, especially on the face, which is thought to function as camouflage, enhancing crypsis (Hölldobler & Wilson, 1986). Highly specialized spatulate setae may be instrumental in acquisition and adherence of the clay layer (Hölldobler & Wilson, 1986)." ‎

Nomenclature

The following information is derived from Barry Bolton's Online Catalogue of the Ants of the World.

• oxente. Eurhopalothrix oxente Celante & Celante, in Celante et al., 2024: 216, fig. 1 (w.) BRAZIL (Pernambuco).

Type Material

• Holotype: Worker; Brasil – PE, Petrolina, Serrote do Urubu, 19–20/12/2020, Lat. -9.368035, Long. -40.379047, LMSAAI61, LMS60AA, collector: G. L. Celante [MFCE014368]. Deposited at MFCE-LMS.
• Paratypes: seven workers collected in the same location as the holotype. Two specimens will be deposited at CPDC (MFCE014367, MFCE014369), two at DZUP (MFCE014370, MFCE014371), two at INPA (MFCE014376, MFCE014377), and one at MZSP (MFCE014372). Furthermore, five specimens were kept in wet storage (ethyl alcohol), deposited at MFCE/LMS (MFCE014378, MFCE014379, MFCE014380, MFCE014381, and MFCE014382).

References

• Celante, G.L., Celante, J.M.G.B., de Sales Nunes, V., Jahyny, B.J.B. 2024. Eurhopalothrix oxente sp. nov. (Hymenoptera: Formicidae), a new riparian species of São Francisco River, northeastern Brazil. Revista Chilena de Entomología 50 (2): 213-225 (doi:10.35249/rche.50.2.24.11).