Ligidium pacolet Recuero & Caterino, 2025, sp. nov.
Creators: name: Recuero, Ernesto
name: Caterino, Michael S.
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Isopoda
Ligiidae
Ligidium
Ligidium pacolet

description: Ligidium pacolet sp. nov.
urn:lsid:zoobank.org:act: 6A3E7CC8-1EF9-4451-889E-81878B6B5250
Figs 10–11
Ligidium sp. 5 – Recuero & Caterino 2024: table 1 (in part).
Diagnosis
This new species is characterized by its male pleopod 2 endopodite presenting a soft, long, slender excrescence rising ventrally in the distal margin of the tip, close to its inner corner, and projected caudally or inwards. It also can be identified from all other Appalachian species based on molecular data, representing a distinct evolutionary lineage.
Etymology
A noun in apposition, in reference to the Pacolet River area where the species has been found.
Material examined
Holotype
USA – North Carolina • ♂; Polk Co., North Pacolet River; 35.2221° N, 82.3059° W; 384 m a.s.l.; 15 Feb. 2022; M. Caterino, E. Recuero, C. Harden and P. Wooden leg.; GenBank no: OR169911 (Cox1); USNM, CUAC000171345.
Paratypes
USA – North Carolina • 2 ♂♂; same data as for holotype; CUAC000171341, CUAC000171342 • 1 ♀; same data as for holotype; CUAC000171343.
Description
Body length of males 5.5–6.1 mm, of female 7.9 mm; width (at pereonite 4) of males 2.6–2.9, of female 3.6 mm. Color in ethanol (Fig. 10) dorsally dark brown with large off-white spots, with a conspicuous dark brown longitudinal medial stripe running from pereonite 1 to pereonite 7, frequently broken with light spots in the caudal margin of pereonites, which carry dark brown transverse bands; epimera dark brown with large white spots at the base and sometimes smaller white spots in the external margin; pleonites 1–4 with two pairs of off-white spots, pereonite 5 (and rarely 4) with a single pair; telson with two large white spots laterally, merging caudally with the white anchor-shaped spot; head marbled brown, with white areas above the eyes; antennae dark brown with large white spots in basal segments and a white setae bundle in the flagellum; uropod brown with inner part of basipodite white; pereopods brown and white, pleopods mostly white. Antennule (Fig. 11G) three-segmented; first segment about 1.7–1.8 times as long as wide, 3 spiniform setae in its distal border; second segment about 2.5–2.6 times as long as wide, also bearing 3 strong spiniform setae in the distal border; third segment with rounded apex and a single seta. Antennae (Fig. 11F) with 5 segmented peduncle, relative size of antennomeres 5>4>3>2=1; antennal flagellum with 11–12 articles. Dactylus of pereopods with outer claw longer than inner one; no sexual dimorphism observed in pereopods 1 (Fig. 11H) and 7 (Fig. 11I). Male pleopod 1 endopodite (Fig. 11A) with narrow projection truncated distally, bearing 3–4 strong, blunt setae, up to 1.3 times as long as endopodite; caudal and inner margins with pilose setae. Pleopod 1 exopodite (Fig. 11B) with broadly rounded caudal margin bearing 3–5 strong, blunt setae, 0.8–0.9 times as long as exopodite; external margin with 2–3 short setae, a few short piliform setae in the frontal external corner and in the inner margin. Male pleopod 2 exopodite (Fig. 11C) 2.1–2.3 times as wide as long; inner and most part of frontal margin with dense, hairy setation; caudal margin convex. Male pleopod 2 endopodite (Fig. 11D–E) with a broad tip, bearing a soft, long, slender excrescence rising ventrally at its distal margin near the inner corner; inner margin of stem with minute spiniform setae, denser at the base and absent well before the tip. Telson (Fig. 10) with caudal margin obtusely produced, with a sinuate profile. Uropod (Fig. 11J) with endopodite 1.3–1.4 times as long as exopodite when not broken, and about 2 times as long as basipodite.
Distribution
The species is known only from its type locality, by the North Pacolet River near Saluda, North Carolina, along the boundary between the Blue Ridge Mountains and the Piedmont Region (Fig. 10). All studied specimens have been collected in moist leaf litter from deciduous forest.
Remarks
Ligidium pacolet sp. nov. corresponds with one of the two lineages named as Ligidium sp. 5 in Recuero & Caterino (2024a). It was clustered together with L. whiteoak sp. nov. in that paper given their morphological and genetic affinities, although species delimitation methods recognized the two species using multilocus data for species delimitation (BPP), or even three with Cox1 single-locus species delimitation methods (ASAP, mPTP) (Supp. file 1). It belongs to a clade including L. blueridgensis and L. whiteoak, being genetically closer to the latter (Fig. 1A). They are also morphologically close, all presenting an excrescence projecting from the male pleopod 2 endopodite; in L. pacolet the excrescence is slender and rises medially or near the inner corner from the margin of the tip, projecting caudally or inwards. In L. blueridgensis the excrescence is also slender, projecting from the inner tip corner rising from the dorsal surface near the margin, and projecting caudally and inwards. Ligidium whiteoak presents a broader excrescence, almost as wide as the endopodite stem, rising dorsally and medially from the caudal margin of the tip and projecting caudally and slightly outwards. The stem of male pleopod 2 endopodite in L. pacolet sp. nov. is slightly broadened in the distal third, while in L. blueridgensis and L. whiteoak its width is constant. The projection of male pleopod 1 endopodite is narrower in L. pacolet than in the other two species. All three gene fragments analyzed are informative to identify this species, with high genetic p-distances for Cox1, moderate to high for NaK and 28S fragments (Supp. file 1), forming a reciprocally monophyletic clade in all cases.
description: Published as part of Recuero, Ernesto & Caterino, Michael S., 2025, Is there anybody (new) out there? Seven new species of Ligidium (Isopoda, Oniscidea, Ligiidae) from the Southern Appalachians, eastern North America, pp. 133-170 in European Journal of Taxonomy 976 on pages 149-152, DOI: 10.5852/ejt.2025.976.2783, http://zenodo.org/record/14844794