Pachygnathus americanus, Uusitalo, 2025

Pachygnathus americanus sp. nov.

( Figs. 10A–F, 11A–I)

Pachygnathus sp. — Vázquez et al. 2011: 57; Vázquez González et al. 2016: 142; Vázquez-Rojas et al. 2016: 21, Remarks.

Description. Dorsum (n= 1 female, Fig. 10A, B, Remarks). Length 376 µm; soft integument slightly undulating; prominent dorsal neotrichy; ciliated setae longer in caudal segments; prodorsal setae sparsely ciliated, naso and sensillar area connected by sclerotic band filling up entire distance between setae vi, one pair of setae on in -area, setae exp above anterior pair of eyes.

Venter ( Fig. 10E, F). Genital valve with 17 genital setae of various lengths; 4 anal setae per valve.

Gnathosoma ( Figs. 10C, D, 11I). Chelicera beak-like with a few minute teeth on both digits, and without cheliceral setae; subcapitulum with two pairs of adoral setae; reduced rutella with minute lobes distally; four sparsely barbed palpal eupathidia, clearly separate from each other.

Legs ( Fig. 11A–H). Solenidial formula for tarsi, tibiae, genua and femora on legs I, II, III and IV, respectively: 2- 1-0-0, 2\3-2-2-0, 3-2-2-1, 5-0-0-0, solenidion ω2 near adaxial end of lyrifissure, famulus I peg-like distally, famulus II a tiny rod abaxially.

Type material. Holotype female (on slide) as Pachygnathus sp. from leaf litter (hojarasca), JBPM ( Jardin Botánico de Puerto Morelos), 20°50’31,2’’N 86°54’10,7’’W, Puerto Morelos, Quintana Roo, Mexico, 20 November 2014, María Magdalena Vázquez. The material will be deposited in the CNCA (Colección Nacional de Acaros) at the Instituto de Biología at UNAM (Universidad Nacional Autonóma de México), Mexico City. GoogleMaps

Differential diagnosis. This species is closely related to the neotrichous species Pachygnathus villosus Dugès [in Oken], 1836 from Europe by having slightly undulating soft integument, setae vi on the prodorsal shield and one pair of setae on the prodorsal in -area. They are distinguished by having the prodorsal setae sparsely ciliated in P. americanus ( Fig. 50D) (vs. not so bush-like as in P. villosus , see Uusitalo 2010: fig. 52) and there are 5 solenidia on femora I ( Fig. 11C vs. 2 solenidia, fig. 56 in Uusitalo 2010). Pachygnathus americanus has found in the tropics, whereas P. villosus is a European species. Another neotrichous species, P. wasastjernae Uusitalo, 2010 from the Baltic Sea area has 5–7 solenidia on femora I, but the integument is strongly undulated and there are two pairs of setae on the in -area ( Uusitalo 2010: figs 60–67). Pachygnathus nasutus Uusitalo et al., 2020 from South Africa has a holotrichous dorsum in all stages ( Fig. 10G; Uusitalo et al. 2020: fig. 27, Remarks) and femora I with 3 solenidia.

Remarks. The holotype specimen is badly folded. Only about half of the prodorsum could be properly reconstructed ( Fig. 10A), and the number of dorsal setae per segment is roughly correct, but the locations are unreliable ( Fig. 10B).

The specimens as Pachygnathus sp. from Sian Ka’an, Cozumel and Belize by Vázquez et al. 2011: 57 and Vázquez González et al. 2016: 142 are deposited in the insect collection of the University of Quintana Roo, Mexico, and are currently not available for study (Dr. Ignacio Vázquez Rojas, in litt.).

The illustration of a holotrichous adult’s dorsum ( Pachygnathus nasutus , Fig. 10G) has not been published before.

Etymology. The specific name refers to the distribution of the species.

Genus Amphialycus Zachvatkin, 1949

Type species: Amphialycus pentophthalmus Zachvatkin, 1949 from Ukraine; by original designation .

Differential diagnosis. The genus has robust and elongated chelicerae; finely striated anterior pair of eyes; and densely setulated empodia like in Orthacarus Zachvatkin, 1949 , but can be differentiated from the latter by having densely ciliated dorsal setae; roundish body; and prodorsal setae resembling dorsal setae. Other diagnostic features are as follows: naso is present; distance between prodorsal setae vi is equal to the distance between sensilla ve; setae in are pubescent; 4–5 palpal eupathidia are close to each other but separated; legs II, III and IV are not bent or are shortened; the anus is ventral ( Figs. 12–15, 50G, H, I). The other genera of the tribe Alycini have either robust and non-elongated ( Alycus and Odontoalycus ) or beak-like ( Pachygnathus ) chelicerae.