Myanmarorchestia seabri Hou

Hou, Zhonge & Zhao, Shuangyan, 2017, A new terrestrial talitrid genus, Myanmarorchestia, with two new species from Myanmar (Crustacea, Amphipoda, Talitridae), ZooKeys 705, pp. 15-39 : 20-25

Myanmarorchestia seabri Hou sp. n. Figs 7, 8, 9, 10, 11, 12, 13

Material examined.

Holotype: male (IZCAS-I-A1690-1), 10.0 mm, Kampetlet (21.20°N, 94.03°E), altitude 1585 m, Chin State, Myanmar, May 17, 2014, collected by Peter Jäger. Paratype: female (SMF50716), 10.0 mm (head and gnathopod I missing), same data as holotype, GenBank accession number MF663278; paratypes, 2 males (SMF50717).

Etymology.

The specific name is derived from abbreviation of the Southeast Asia Biodiversity Research Institute, Chinese Academy of Sciences (CAS-SEABRI); noun in apposition.

Diagnosis.

Eyes rounded; maxilla I palp with one article; male gnathopod II merus and carpus protuberant on posterior margin, propodus with tumescence, sub-triangular; coxal gills convoluted; telson bare on surface.

Description of male.

Holotype (IZCAS-I-A1690-1), 10.0 mm.

Head. (Fig. 7A): Eyes rounded, medium in size.

Antenna I (Fig. 7B): peduncle articles I–III in length ratio 1.0: 1.1: 1.4; flagellum with six articles and one fine distal article, a little shorter than peduncle, each article with short distal setae.

Antenna II (Fig. 7C): peduncle articles III–V in length ratio 1.0: 2.0: 2.8, with setae on anterior and posterior margins; flagellum with 14 articles, each article with setae on dorsal and ventral margins.

Upper lip (Fig. 7D): ventral margin rounded, bearing minute setae.

Mandible (Fig. 7F, G): incisor of left mandible with five teeth; lacinia mobilis with four teeth; spine row with four plumose setae; molar with a plumose seta; incisor of right mandible with four teeth, lacinia mobilis bifurcate, with small teeth.

Lower lip (Fig. 7E): inner lobes indistinct, outer lobes covered with thin setae.

Maxilla I (Fig. 7H): inner plate with two terminal strong setae, outer plate with nine serrated apical spines, palp with one fused article.

Maxilla II (Fig. 7I): 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 spines.

Maxilliped (Fig. 7J, K): inner plate with three stout apical spines and 14 plumose setae; outer plate bearing five setae on interior margin, some simple setae and two plumose setae apically; palp with four articles, first two articles broad; articles I–III in length ratio 1.0: 1.0: 0.6; articles II-III with fine setae; article III with two spines on distal end, two setae on exterior margin and five setae on ventral surface; article IV very short, with one spine and two simple setae apically.

Pereon.Gnathopod I (Fig. 8A, B): coxal plate bearing nine setae on distal margin, anterior margin processed proximally; basis with fine setae on anterior and posterior margins; merus, carpus, and propodus in length ratio 1.0: 1.7: 1.1; merus bearing setae on posterior margin; carpus with setae on anterior and posterior margins; propodus with setae on anterior margin and two spines accompanied by setae on posterior margin; dactylus with one spine on posterior margin and three spines at hinge of unguis.

Gnathopod II (Fig. 8 C–E): coxal plate distal margin with eleven setae, posterior process prominent; basis with two fine setae on posterior margin; merus protuberant on posterior margin; carpus 1.4 times as long as wide, with tumescent hump at posterodistal comer; propodus with tumescence, subtriangle, with setae on surface, palm margin with a row of spines on interior and exterior sides; dactylus as long as palm, with setae on posterior margin and two setae at tip.

Pereopod III (Fig. 9A, F): coxal plate with posterior cusp, bearing 12 setae on distal margin; basis longest, with spines on anterior and posterior margins; merus, carpus, and propodus in length ratio 1.0: 0.7: 1.0; carpus and propodus with spines on posterior margins; dactylus with two spines at hinge of unguis. Pereopods III–IV simplidactylate.

Pereopod IV (Fig. 9B, G): similar to pereopod III; shorter; coxal plate with posterior cusp, bearing ten setae on ventral margin; merus, carpus, and propodus in length ratio 1.0: 0.8: 1.1, dactylus weakly pinched.

Pereopod V (Fig. 9C, H): coxal plate bilobed, anterior lobe bigger than posterior lobe, bearing seven setae and one seta on anterior and posterior lobes, respectively; basis suboval, with five spines on anterior margin and 11 setae on posterior margin, anterodistal corner with two spines; merus, carpus, and propodus in length ratio 1.0: 1.2: 1.7, with spines on both margins; dactylus with two spines at hinge of unguis.

Pereopod VI (Fig. 9D, I): coxal plate bilobed, anterior lobe much smaller than posterior lobe, bearing five setae on posterior lobe; basis suboval, with seven spines on anterior margin and 12 setae on posterior margin, anterodistal corner with two spines; merus, carpus, and propodus in length ratio 1.0: 1.2: 1.6, with spines on both margins; propodus and dactylus slender, dactylus with two spines at hinge of unguis.

Pereopod VII (Fig. 9E, J): coxal plate non-lobate, shallow, with two setae on anterodistal corner and four setae on posterodistal; basis oval, with seven spines on anterior margin and 14 setae on posterior margin, anterodistal corner with two spines; merus, carpus, and propodus in length ratio 1.0: 1.2: 1.7, with spines on both margins; propodus and dactylus slender, dactylus with two spines at hinge of unguis.

Coxal gills (Figs 8F, 9 K–N): present on gnathopod II and pereopods III–VI; gill of gnathopod II and pereopods III–V lobed and convoluted, one or two lobes with ridged margins; gill of pereopod VI lobed and convoluted.

Pleon.Epimeral plates (Fig. 10 A–C): acuminate posterodistally, distal margins without armature; plate I with four fine setae on posterior margin; plate II with five fine setae on posterior margin; plate III shorter, with four fine setae on posterior margin.

Pleopods I–III (Fig. 10 D–F): similar, peduncle with two retinacula on interior margin, exterior margin with dense plumose setae; outer ramus approx. 80% of peduncle, outer ramus shorter than inner ramus, both inner and outer rami fringed with plumose setae.

Urosome.Uropods I–III (Fig. 10 G–I): uropod I peduncle longer than rami, with three spines on interior margin and four spines on exterior margin; inner ramus with five spines on interior side and five terminal spines; outer ramus with four terminal spines. Uropod II short, peduncle bearing one spine on interior margin and six spines on exterior margin; inner ramus with four spines on interior side and five terminal spines; outer ramus slightly shorter than inner ramus, variation in armature, the holotype and one paratype with one spine on interior side and some small teeth distally, while the other paratype marginally bare but with three terminal spines as that of female (Fig. 12K). Uropod III peduncle expanded, with fine setae on ventral margin, two robust setae on dorsal margin and two posterodistal spines; ramus short, 0.6 times as long as peduncle, with one long slender spine and one short spine apically.

Telson (Fig. 10J): notched, each lobe with one apical spine.

Description of paratype female

(SMF50716), head and gnathopod I missing, 10.0 mm.

Pereon.Gnathopod II (Fig. 11 A–C): coxal plate distal margin with 17 setae, posterior process prominent; basis slender, with six fine setae on anterior margin and two fine setae on posterior margin; merus protuberant on posterior margin; carpus with tumescent hump at posterodistal comer, with two setae on distal end and four setae on anterior margin; propodus with tumescence, with setae on surface and palm margin; dactylus with two setae at tip.

Pereopods III–VII (Fig. 12 A–E): similar to those of male.

Coxal gills (Fig. 12 F–I): similar to those of male, coxal gill of pereopod V lost.

Oostegites (Fig. 11 D–G): present on gnathopod II and pereopods III–V, oostegites of gnathopod II and pereopods III–IV slender, oostegites of pereopod V expanded and smallest.

Urosome.Uropods I–III (Figs 12J, K; 10K): uropod I (Fig. 12J) peduncle longer than rami, with four spines on interior margin and five spines on exterior margin; inner ramus with four spines on interior side and five terminal spines; outer ramus with four terminal spines. Uropod II (Fig. 12K) short, peduncle bearing two spines and one fine seta on interior margin and six spines on exterior margin; inner ramus with four spines on interior side and five terminal spines; outer ramus shorter than inner ramus, with three terminal spines. Uropod III (Fig. 10K) peduncle expanded, with three stiff setae on dorsal margin and two posterodistal spines; ramus short, 0.5 times as long as peduncle, with one long slender spine and one short spine apically.

Telson (Fig. 10L): notched, left lobe with two apical spines and right lobe with one apical spine.

Habitat.

This species was collected by sieving leaf litter along a stream in a secondary forest (Fig. 13).

Remarks.

Myanmarorchestia seabri Hou, sp. n. can be distinguished from M. peterjaegeri Hou, sp. n. by the following characters ( M. peterjaegeri Hou, sp. n. in parentheses): palp of maxilla I with one fused article (with two small articles); gnathopod II of male subtriangle, with bigger tumescence than that of M. peterjaegeri Hou, sp. n., palm margin with a row of spines on interior and exterior sides (with setae), dactylus elongate (short); coxal gills with one or two lobes ridged (with more filamentous projections or ridged margins); uropod III peduncle with two posterodistal spines (with one posterodistal spine); telson surface bare (with nicks). In addition, M. peterjaegeri Hou, sp. n. and M. seabri inhabit separate habitats, with up to 500 m elevation difference.

The uncorrected p-distance between M. peterjaegeri Hou, sp. n. and M. seabri Hou, sp. n. is 18.8% for COI. This significant differentiation confirmed that they are two different new species, in comparison with previous molecular threshold used for crustacean species delimitation ( Lefébure et al. 2006, Hou et al. 2009).