Orthacarus oblongus (Halbert, 1920), 2025

Orthacarus oblongus (Halbert, 1920) comb. nov.

( Fig. 16A–G)

Alicus oblongus Halbert, 1920: 140 , pl. 23, figs. 23a-c, erroneous orthography of Alycus C.L. Koch ; holotype from Malahide,

Ireland, from orange lichen zone at NMI (National Museum of Ireland). Pachygnathus oblongus .— Thor & Willmann 1941: 138; Baker & Bayliss 2005: 288. Amphialycus (Orthacarus) oblongus .— Uusitalo 2010: 58, figs. 82–87; Vázquez-Rojas et al. 2016: 21; Uusitalo et al. 2020: 321,

figs. 76–89. Alycus? roseus .— Womersley 1944: 139. Orthacarus tremli .— Zachvatkin 1949: 292, figs. 1–5.

Description. Dorsum (n= 2 females, Figs. 16A, B). Length 300–500 µm; neotrichous setal pattern dorsally and on ventral side; naso absent, prodorsal setae vi, sce and exp sparsely ciliated (reduced), sensilla ve and sci filamentous, distance between counterparts of setae vi exceptionally small.

Venter . Genital valves each with 12–18 genital setae; anal valves terminally with 7–8 setae, Remarks.

Gnathosoma ( Fig. 16G). Pair of smooth cheliceral setae abaxially; rutella widening to apical lobes and a pointed process, one pair of adoral setae; distally narrow palpal tarsi with four basally fused, microtrichous eupathidia.

Legs ( Figs. 16C–F). Claw-like empodium multisetulate; solenidial formula for tarsi, tibiae, genua and femora of legs I, II, III and IV, respectively: 2-1-0-0, 2-2-2-0, 3-2-0-1, 1-0-0-0

Material examined. 1 female (on slide) from leaf litter (hojarasca), floodable low forest (selva baja inundable), Sian Ka’an , Quintana Roo , Mexico, 15 November 1996, María Magdalena Vázquez; several high-quality photos of two adults, 1 protonymph and 1 larva from coastal dune, leaf litter, JBPM ( Jardin Botánico de Puerto Morelos), 20°49’24,9’’N 86°53’53,6’’W, Puerto Morelos, Quintana Roo GoogleMaps , Mexico, 30 April 2015, María Magdalena Vázquez. Material is deposited in the LAAH (Laboratorio de Acarología ” Anita Hoffmann ”), Faculty of Sciences at UNAM ( Universidad Nacional Autonóma de México), Mexico City .

Differential diagnosis. This species differs from other neotrichous species of the genus Amphialycus by having the edaphomorphisms listed in the diagnosis of the genus. This species differs from another (still undescribed) species of the genus Orthacarus ( Fig. 54) by having both pairs of prodorsal sensilla (ve and sci) filamentous, abaxially inserted cheliceral setae and the solenidial pattern as expressed in Description above.

Remarks. Detailed figures of the dorsum, venter, various organs, and juvenal stages of O. oblongus [as Amphialycus (Orthacarus) oblongus ] has already been published twice - from Europe ( Uusitalo 2010: 58, figs. 82–89) and from South Africa ( Uusitalo et al. 2020: 321, figs. 76–89). The figures in the present study focus on illustrating leg solenidia (black arrows) and variation of prodorsal setae. The reduced setae vi, sce and exp are less ciliated in specimens from the European and South African populations of Amphialycus (Orthacarus) oblongus ( Uusitalo 2010: 127, fig. 82 and Uusitalo et al. 2020: 322, fig. 76), and the lengths of the columnar and bushy seta in also varies when compared to the Mexican specimen ( Fig. 16A). However, the ciliation of the prodorsal setae in a specimen from European unpublished material ( Fig. 16B, from Italy) corresponds well to those form of the Mexican counterparts. Considering that the solenidial formulae are similar in specimens from the three continents - despite limited material - it is fair to assume that the observed differences are due to intraspecific variation and the specimens are conspecific. This species has also been reported from Australia as Alycus? roseus ( Womersley 1944: 139, fig. 3F–I), and it may have an anthropochorous distribution.