Floresorchestia xueli Tong & Hao & Liu & Li & Hou 2021, sp. nov.

Floresorchestia xueli Tong & Hou, sp. nov.

( Figs 2–8)

Material examined. Holotype ♂, 8.0 mm (IZCAS-I-A2590-1); CHINA, Yunnan Province, Yingjiang County, Xueli Village; 24.44N, 97.60E; 605 m a.s.l.; 16 November 2017; ZG Chen leg. Paratype ♀, 9.0 mm (IZCAS-I-A2590- 2), same data as holotype. Other materials, two males and two females (IZCAS-I-A2590-3, 4, 5, 6), same data as holotype. Two male specimens were used for molecular analysis, and the sequences were submitted to GenBank (MZ 224489 and MZ 224490).

Etymology. The species name is derived from the name of the type locality; noun in apposition.

Habitat. A terrestrial species living on the wet forest floor near streams, at an altitude of 600 m. The specimens were collected from rotten wood on the floor, plant roots, and under stones. The habitat is characterised by a cool temperature, damp and without direct sunlight. The shelter of plants and streams are important conditions for the formation of the habitat.

Diagnosis. Male gnathopod I merus protuberant medioposteriorly; female gnathopod II merus with protuberance posteriorly; left mandible lacinia mobilis with four teeth and right mandible lacinia mobilis bifurcate; telson apically notched, with one slender facial spine and two terminal spines; coxal gills complexly lobed and convoluted; epimeral plates I–III without slits.

Description of male. Based on holotype (IZCAS-I-A2590-1), 8.0 mm (Fig. 2).

Head. Eyes rounded. Antenna I (Fig. 3A): reaching 38% of antenna II, peduncle articles 1–3 in length ratio 1.0: 0.8: 1.1, with distal spines; flagellum with four articles, last article tiny, each article with short distal setae. Antenna II (Fig. 3B): peduncle articles 3–5 in length ratio 1.0: 2.3: 3.2; flagellum with 13 articles. Upper lip (Fig. 3C): ventral margin rounded, bearing minute setae. Mandible (Fig. 3D, E): left mandible incisor with five teeth; lacinia mobilis with four teeth; spine row with four plumose setae; molar well developed and with a plumose seta. Right mandible incisor with five teeth, lacinia mobilis bifurcate. Lower lip (Fig. 3H): inner lobes indistinct, outer lobes covered with fine setae. Maxilla I (Fig. 3F): inner plate thin, with two terminal plumose setae and a group of fine setae on outer margin; outer plate with nine terminal serrate setae; one small articulate palp present. Maxilla II (Fig. 3G): inner plate narrower and shorter than outer plate, with one plumose seta and numerous simple setae on medial margin; outer plate with two rows of apical setae. Maxilliped (Fig. 3I): inner plate with three stout spines distally; outer plate with apical setae; palp article 4 reduced, button-shaped.

Pereon. Gnathopod I (Fig. 4A–C): sexually dimorphic; coxal plate ventral margin rounded, with four small spines; basis anterior and posterior margins with short setae; merus, carpus, and propodus in length ratio 1.0: 1.5: 1.1; merus protuberant medioposteriorly, bearing four spines on the base of the protuberance; carpus anterior and posterior margins with setae; propodus distally expanded, with a row of spines on both faces, palm margin well developed exceeding dactylus length, with long setae medially; dactylus with a spine on curved margin and a stiff seta at the joint of unguis. Gnathopod II (Fig. 4D, E): sexually dimorphic; coxal plate wider than gnathopod I coxal plate, with a short posterior cusp, ventral margin spinose; basis stout, posterior margin with minute spines; propodus enlarged, 1.5 times as long as wide, palmar margin smoothly convex, fringed with spines; dactylus beyond propodus palm.

Pereopods III–VII (Fig. 5A–E), cuspidactylate. Pereopod III (Fig. 5A, F): coxal plate with a posterior cusp, ventral margin with short spines; merus to propodus anterior margins with fewer spines than posterior margins; merus, carpus, and propodus in length ratio 1.0: 0.7: 0.9; carpus and propodus with spines on posterior margins; dactylus with two spines at hinge of unguis. Pereopod IV (Fig. 5B, G): shorter than pereopod III; coxal plate with a shorter posterior cusp, ventral margin with seven setae; merus, carpus, and propodus in length ratio 1.0: 0.8: 1.1, dactylus with two spines at hinge of unguis. Pereopod V (Fig. 5C, H): coxal plate bilobed, anterior lobe larger than posterior lobe, bearing two setae on posterior lobe; basis suboval, with spines on both margins; merus, carpus, and propodus in length ratio 1.0: 1.1: 1.5, with spines on both margins; dactylus with two spines at hinge of unguis. Pereopod VI (Fig. 5D, I): coxal plate bilobed, anterior lobe much smaller than posterior lobe, bearing two setae on posterior lobe; basis suboval, with seven spines on anterior margin and many setae on posterior margin; merus, carpus, and propodus in length ratio 1.0: 1.1: 1.5, with spines on both margins; propodus and dactylus slender, dactylus with two spines at hinge of unguis. Pereopod VII (Fig. 5E, J): coxal plate unilobate, shallow; basis oval, with five spines on anterior margin and 13 setae on posterior margin; merus, carpus, and propodus in length ratio 1.0: 1.1: 1.5, with spines on both margins; propodus and dactylus slender, dactylus with two spines at hinge of unguis.

Coxal gills (Fig. 6A–E): present on gnathopod II and pereopods III–VI, complexly lobed and convoluted.

Pleon. Epimeral plates (Fig. 4K–M): plate I rounded posterodistally, with one fine seta on posterior margin; plates II–III acuminate posterodistally, with one fine seta on posterior margin, respectively; plates I–III without slits.

Pleopods I–III similar (Fig. 4I): outer ramus subequal in length to peduncle, inner ramus about 80% of outer ramus, both inner and outer rami fringed with plumose setae.

Urosome. Uropods I–III (Fig. 4F–H): uropod I peduncle slightly longer than ramus, inner margin with four spines and outer margin with three spines; inner ramus with five marginal spines and four terminal spines; outer ramus marginally bare, with three terminal spines. Uropod II shorter than uropod I; peduncle subequal in length with rami, inner margin with one spine and outer margin with three spines; inner ramus with three margina spinesl and four terminal spines; outer ramus with three marginal spines and three terminal spines. Uropod III peduncle with two subdistal spines; ramus narrower and shorter than peduncle, with four terminal spines.

Telson (Fig. 4J): bilobed, apically notched, with one slender facial spine and two terminal spines per lobe.

Description of paratype female (IZCAS-I-A2590-2), 9.0 mm (Fig. 2).

Pereon. Gnathopod I (Fig. 7A, B): coxal plate ventral margin rounded, with five small spines; basis slender and long, with short setae on anterior and posterior margins; merus, carpus, and propodus in length ratio 1.0: 2.1: 1.5; merus without protuberance humps, bearing four spines on posterior margin; carpus and propodus with spines on anterior and posterior margins; dactylus with two spines at hinge of unguis. Gnathopod II (Fig. 7C–E): coxal plate with cuspidate posterior margin, ventral margin spinose; basis stout, anterior and posterior margins with minute spines; merus with protuberance posteriorly and four spines; carpus and propodus expanded, with protuberance posteriorly, propodus palm with a row of spines on both faces; dactylus about half of the propodus palm.

Pereopods III–VII (Fig. 8A–L): similar to those of male.

Oostegites (Figs 7C, 8A, B): present on gnathopod II and pereopods III–V.

Remarks: Floresorchestia xueli Tong & Hou, sp. nov. is closely related to F. hanoiensis from Vietnam in gnathopods I–II sexually dimorphic, the shape of pereopods III–VII, and apically notched telson with three spines on each lobe. The new species can be distinguished from F. hanoiensis by the following characters (F. hanoiensis in parentheses): (1) left mandible lacinia mobilis with four teeth (with five weak dentations); right mandible lacinia mobilis bifurcate, with small teeth (with many weak teeth); (2) maxilla I inner plate with a group of setae on outer margin (without setae); and (3) uropod II outer ramus with three marginal spines (with one mid-marginal spine).

Floresorchestia xueli Tong & Hou, sp. nov. can be distinguished from F. boonyanusithii by the following characters (F. boonyanusithii in parentheses): (1) epimeral plates II–III without epimeral slits (with epimeral slits); (2) left mandible incisor with five teeth (with four teeth); (3) maxilla I inner plate with a group of setae on outer margin (without setae); and (4) telson with three spines per lobe (four spines per lobe). It also can be distinguished from F. buraphana by the following characters (F. buraphana in parentheses): (1) epimeral plates II–III without epimeral slits (with epimeral slits); (2) left mandible lacinia mobilis with four teeth (with five teeth); (3) telson with three spines per lobe (five spines per lobe); (4) coxal gills convoluted (simple).

We downloaded nine COI sequences of the genera Floresorchestia and Gazia from GenBank (Table 1). Molecular analyses showed high interspecific divergences. The uncorrected p-distances between Floresorchestia xueli Tong & Hou, sp. nov., the other five Floresorchestia species and Gazia gazi are more than 19% (Table 1), larger than the accepted threshold (16%) for crustacean species delimitation (Hou & Li 2010; Lefébure et al. 2006). Therefore, morphological and molecular data support the idea that Floresorchestia xueli Tong & Hou, sp. nov. is a species new to science.

The new species occurs at the most distant sites from the coastline (more than 600 km; Fig. 1), whereas most Floresorchestia species mainly spread along the coastal areas. The terrestrial talitrids are considered to have arisen from coast dwelling species and possess a number of features for adaptation (Friend & Richardson 1986). The convoluted gills and the absence of epimeral slits might be some of the adaptations to terrestrial habitat. The biogeography and character evolution of Floresorchestia xueli Tong & Hou, sp. nov. in terrestrial habitat needs to be further studied.