Pseudocrangonyx elegantulus Hou

Zhao, Shuangyan & Hou, Zhonge, 2017, A new subterranean species of Pseudocrangonyx from China with an identification key to all species of the genus (Crustacea, Amphipoda, Pseudocrangonyctidae), ZooKeys 647, pp. 1-22 : 5-9

Pseudocrangonyx elegantulus Hou sp. n. Figs 2, 3, 4, 5, 6, 7

Material examined.

Holotype: female (IZCAS-I-A1602-1), 7.5 mm, Wulongdong National Forest Park (113.943°E, 35.716°N), altitude 770 m, Wulong Town, Linzhou City, Henan Province, China, June 19, 2014, collected by Y. Li and J. Liu. Paratype: male (IZCAS-I-A1602-2), 6.3 mm, same data as holotype.

Etymology.

The specific name is from Latin elegantulus (elegant), in reference to the peculiar shape; adjectival, masculine.

Diagnosis. Female larger than male; eyes absent; lateral cephalic lobe rounded; inferior antennal sinus indistinct; both male and female with calceoli on antenna II; coxal gills present on gnathopod II and pereopods III–VI; sternal gills absent; epimeral plate I without armature on distal margin; urosomite III dorsal margin without armature; uropod I peduncle with one basofacial spine; inner ramus of male uropod II with two serrate and four simple robust terminal spines accompanied by one seta; uropod III peduncle 0.30 times as long as outer ramus and terminal article of the outer ramus a little shorter than adjacent spines.

Description of holotype female

(IZCAS-I-A1602-1), 7.5 mm.

Head. (Fig. 2A): eyes absent; lateral cephalic lobe rounded; inferior antennal sinus indistinct.

Antenna I (Fig. 2B, C): peduncle articles 1-3 in length ratio 1.0: 0.7: 0.4, with distal setae; flagellum with 16 articles, articles 3-15 with aesthetascs; accessory flagellum with two articles, subequal to the first article of primary flagellum; both primary and accessory flagella with short distal setae.

Antenna II (Fig. 2D, E): peduncle articles 3-5 in length ratio 1.0: 2.2: 2.9, with spines accompanied by setae; flagellum with seven articles, with one or two spines and setae on first three articles and with setae on the rest articles; calceoli of crangonyctid type, present on peduncular article 5 and first three flagellum articles; rod-like structures accompanied with setae on first four flagellum articles.

Upper lip (Fig. 2F): ventral margin rounded, bearing fine setae.

Mandible (Fig. 2H, I): incisor of left mandible with five teeth; lacinia mobilis with five teeth; spine row with five serrated spines; articles 1-3 of palp in length ratio 1.0: 2.2: 2.4, second article with ten marginal setae, article 3 with three B-setae, ten D-setae and five E-setae apically; incisor of right mandible with five teeth, lacinia mobilis bifurcate, with small teeth.

Lower lip (Fig. 2G): inner lobes absent, outer lobes covered with thin setae.

Maxilla I (Fig. 2J, K): asymmetrical, left inner plate with four plumose setae; outer plate with seven serrated apical spines; second article of left palp densely setose, with two simple setae and four slender spines apically; second article of right palp with five spines and two slender setae.

Maxilla II (Fig. 2L): inner plate with four plumose facial setae in an oblique row; inner and outer plates with long setae apically.

Maxilliped (Fig. 2M): inner plate with three stout apical spines, two serrated setae, and five plumose setae; outer plate bearing four setae, four serrated spines and five plumose setae apically; palp 4-articulate, articles 1-2 in length ratio 0.7: 1, article 2 with a row of simple setae on interior side and one simple seta on exterior side; article 4 hooked, with five setae at hinge of unguis.

Pereon.Gnathopod I (Fig. 3A, B): coxal plate bearing one fine seta on proximal margin and three setae on anterodistal corner, 1.7 times as wide as deep; basis with long setae on posterior margin, anterior margin bare; merus bearing setae on posterodistal corner; carpus as long as wide, approximately 0.5 times as long as propodus, bearing three clusters of setae along posterior margin, two clusters of setae on anterior margin, and three pectinate setae on posterodistal corner; propodus pear-shaped, palm margin with 16 robust spines, some distally notched; dactylus with one seta on anterior margin and two setae at hinge of unguis, posterior margin dentate.

Gnathopod II (Fig. 3C, D): coxal plate bearing one fine seta on proximal margin, three setae on anterodistal corner and one seta on distal margin; basis with setae on posterior margin, anterior margin bare; merus bearing setae on posterodistal corner; carpus 1.5 times as long as wide, approximately 0.7 times as long as propodus, bearing seven clusters of setae along posterior margin and three pectinate setae on posterodistal corner; propodus stout, palm margin with 14 distally notched spines; dactylus with one seta on anterior margin and two setae at hinge of unguis, posterior margin dentate.

Pereopod III (Fig. 4A, B): coxal plate bearing four setae on anterior margin and two setae on distal margin, 1.4 times as wide as deep; basis with seven setae along anterior margin and long setae on posterior margin; merus, carpus, and propodus in length ratio 1.0: 0.7: 0.8; merus with three spines on anterior margin and four clusters of setae on posterior margin, anterodistal corner with one spine; carpus with one fine seta on anterior margin and two setae on posterior margin, anterodistal corner with one seta and posterodistal corner with two spines accompanied with one seta; dactylus with one plumose seta on anterior margin, one seta on posterior margin, and one seta at hinge of unguis.

Pereopod IV (Fig. 4C, D): similar to pereopod III; coxal plate bearing three setae on anterior margin, 1.6 times as wide as deep; merus, carpus, and propodus in length ratio 1.0: 0.9: 1.0.

Pereopod V (Fig. 4E, F): coxal plate irregular, anterior lobe larger than posterior lobe, bearing four setae and one seta on anterior and posterior lobes, respectively; basis with setae on anterior and posterior margins, respectively; merus, carpus, and propodus in length ratio 1.0: 0.9: 0.9; merus and carpus with spines accompanied by setae on both margins; dactylus with one plumose seta on posterior margin, one seta on anterior margin, and one seta at hinge of unguis.

Pereopod VI (Fig. 4G, H): coxal plate similar to that of pereopod V, with smaller anterior lobe, bearing one seta on posterior lobe; basis with setae on anterior and posterior margins; merus, carpus, and propodus in length ratio 1.0: 1.0: 0.9; merus and carpus with spines accompanied by setae on both margins; dactylus with one plumose seta on posterior margin, one seta on anterior margin, and one seta at hinge of unguis.

Pereopod VII (Fig. 4I, J): coxal plate subtriangular, with two setae on posteroproximal corner; basis with setae on anterior and posterior margins; merus, carpus, and propodus in length ratio 1.0: 1.1: 1.1; merus and carpus with spines accompanied by setae on both margins; dactylus with one plumose seta on posterior margin, one seta on anterior margin, and one seta at hinge of unguis.

Coxal gills: present on gnathopod II and pereopods III–VI; sternal gills absent.

Oostegite (Fig. 4 K–N): narrow, present on gnathopod II and pereopods III–V, with marginal setae.

Pleon.Epimeral plates (Fig. 5 A–C): plate I distally rounded, bearing three fine setae on posterior margin and one seta on posterodistal corner, distal margin without armature; plate II with two spines on distal margin and three fine setae on posterior margin, posterodistal corner rounded with one seta; plate III with two spines on distal margin and two fine setae on posterior margin, posterodistal corner rounded with one seta.

Pleopods I–III (Fig. 5 D–F): similar, peduncle with two retinacula on interior side and one fine seta on exterior distal corner; outer ramus shorter than inner ramus, both inner and outer rami fringed with plumose setae.

Urosome.Urosomites (Fig. 2N): urosomite I with two setae on dorsal margin; urosomite II with two spines on left side and two spines accompanied by one seta on right side; urosomite III dorsal margin without armature.

Uropods I–III (Fig. 5 G–I): uropod I peduncle with one basofacial spine, with three spines on exterior side, interior and exterior distal corners with one spine respectively; inner ramus approximately 0.77 times as long as peduncle, with three spines on interior side, one seta and one spine on exterior side, and six terminal spines accompanied by one seta; outer ramus approximately 0.76 times of inner ramus, with two spines on exterior side and five terminal spines. Uropod II half shorter, peduncle bearing two spines on exterior side and one spine on each distal corner; inner ramus with two spines on interior side, one spine on exterior side, and six terminal spines accompanied by one seta; outer ramus approximately 0.71 times of inner ramus, with two spines on exterior side and five terminal spines. Uropod III with peduncle 0.30 times as long as outer ramus, with one dorsal and three ventral robust spines; inner ramus absent; outer ramus 2-articulate, first article of outer ramus with stiff spines on interior and exterior sides, terminal article 0.19 times of the first article, with three distal setae, a little shorter than adjacent spines.

Telson (Fig. 5J): 1.2 times as long as wide, cleft 0.27 of its length, each lobe with two setae on surface and two distal spines.

Description of paratype male

(IZCAS-I-A1602-2), 6.3 mm.

Head.Antenna II (Fig. 7A): peduncle articles 3-5 in length ratio 1.0: 2.6: 3.0, with setae along anterior and posterior margins; flagellum with six articles, with spines and setae on first article and with setae on the rest articles; calceoli of crangonyctid type present on peduncular article 5 and first two flagellum articles; rod-like structures accompanied with setae on flagellum articles.

Pereon.Gnathopod I (Fig. 6A, B): coxal plate bearing three setae on anterodistal corner, 1.6 times as wide as deep; basis with long setae on posterior margin, anterior margin bare; merus bearing setae on posterodistal corner; carpus 0.8 times as long as wide, approximately 0.5 times as long as propodus, bearing five clusters of setae along posterior margin and two pectinate setae on posterodistal corner; propodus pear-shaped, palm margin with 14 distally notched spines; dactylus with one seta on anterior margin.

Gnathopod II (Fig. 6C, D): coxal plate bearing five setae on distal margin; basis with long setae on posterior margin, anterior margin bare; merus bearing setae on posterodistal corner; carpus 1.5 times as long as wide, approximately 0.7 times as long as propodus, bearing seven clusters of setae along posterior margin; propodus stout, palm margin with 12 distally notched spines; dactylus with one seta on anterior margin.

Pereopods III–VII (Fig. 7 B–F): similar to those of male.

Pereonites I–VI without armature on dorsal margin. Pereonite VII (Fig. 7H): with seven setae on dorsal margin.

Pleon.Pleonites I–III (Fig. 7 I–K): dorsal margins with five, two, and nine setae, respectively.

Urosome.Urosomites (Fig. 7L, M): urosomite I with four setae on dorsal margin; urosomite II with two spines on each side.

Uropods I–III (Fig. 5 K–M): uropod I peduncle with one basofacial spine, with three spines on exterior side, interior and exterior distal corners with one spine respectively; inner ramus approximately 0.73 times as long as peduncle, with two spines on interior side, two simple setae on exterior side, and six terminal spines accompanied by one seta; outer ramus approximately 0.8 times of inner ramus, with two spines on exterior side and five terminal spines. Uropod II shorter, peduncle bearing one spine on exterior side and one spine on each distal corner; inner ramus with two spines on each side, distal part with two serrated and four simple robust spines accompanied by one seta; outer ramus approximately 0.72 times of inner ramus, with one spine on exterior side and five terminal spines. Uropod III peduncle 0.31 times as long as outer ramus, with one dorsal and three ventral robust spines; inner ramus absent; outer ramus bi-articulate, first article of outer ramus with three groups of stiff spines on interior and exterior sides, terminal article 0.18 times of the first article, with three distal setae, a little shorter than adjacent spines.

Telson (Fig. 7G): 1.2 times as long as wide, cleft 0.24 of its length, each lobe with two setae on surface and two distal spines accompanied by one short seta.

Habitat.

This species was collected from groundwater flowing through a cave of the Wulongdong National Forest Park.

Remarks.

Pseudocrangonyx elegantulus sp. n. is clustered with Pseudocrangonyx yezonis Akatsuka & Komai, 1922 supported by high statistical supports in the molecular phylogenetic tree. Unfortunately, the original description of the latter species is poor and no redescription has been published. The following comparisons are based on recent observations (Ko Tomikawa pers. comm.). The new species is morphologically similar to Pseudocrangonyx yezonis in antenna II with calceoli; the armature of gnathopods I and II and pereopods III–VII; both rami of pleopods with more than five articles; urosomite III dorsal margin without armature. It can be distinguished from Pseudocrangonyx yezonis Akatsuka & Komai, 1922 by the following characters ( Pseudocrangonyx yezonis in parentheses): pereonites I–VI without armature on dorsal margin, only pereonite VII with dorsal setae (with long setae on dorsal margins of pereonites I–VII); uropod III terminal article of outer ramus a little shorter than adjacent spines (subequal).

The new species is most similar to Pseudocrangonyx cavernarius Hou & Li, 2003 in the armature of gnathopods I and II and pereopods III–VII; epimeral plate I without armature on distal margin; both rami of pleopods with more than five articles. The new species can be distinguished from Pseudocrangonyx cavernarius Hou & Li, 2003 by the following characters ( Pseudocrangonyx cavernarius in parentheses): antenna II with calceoli (absent); inner plate of maxilla II with four plumose facial setae in an oblique row (with five plumose setae); urosomite I with two setae on dorsal margin (with four clusters of setae); urosomite III dorsal margin without armature (with one pair of fine spines); outer ramus of uropod I with five terminal spines (with four terminal spines); uropod II inner ramus with six terminal spines accompanied by one seta (with five terminal spines) and outer ramus with five terminal spines (with three terminal spines); uropod III peduncle with one dorsal and three ventral robust spines (with three distal spines), terminal article of outer ramus a little shorter than adjacent spines (longer); each lobe of both male and female telson with two setae on surface (with no armature).

The new species is similar to Pseudocrangonyx asiaticus Uéno, 1934, which was redescribed by Uéno (1966), in the accessory flagellum being subequal to the first article of primary flagellum; the armature of gnathopods I and II and pereopods III–VII. It can be distinguished from Pseudocrangonyx asiaticus Uéno, 1934 by the following characters ( Pseudocrangonyx asiaticus in parentheses): antenna II with calceoli (absent); incisor of mandible with five teeth (with 5-6 teeth); mandible spine row with five serrated spines (with 8-10 serrated setae); maxilliped inner plate with three stout apical spines, two serrated setae, and five plumose setae (with five serrated spines and seven plumose setae); sternal gills absent (present on gnathopod II and pereopods III–IV); each lobe of both male and female telson with two setae on surface (with no armature).

The new species is similar to Pseudocrangonyx elenae Sidorov, 2011 in body length (longer than 6.0 mm); the armature of gnathopod I and II and pereopods III–VII; epimeral plate I without armature on distal margin; both rami of pleopods with more than five articles; urosomite III dorsal margin without armature; terminal article of outer ramus of uropod III shorter than adjacent spines. It can be distinguished from Pseudocrangonyx elenae Sidorov, 2011 by the following characters ( Pseudocrangonyx elenae in parentheses): accessory flagellum of antenna I subequal to the first article of primary flagellum (shorter than accompanying flagellar article); antenna II of female with calceoli (absent); mandible spine row with five serrated spines (with six serrated setae); maxilla I with four plumose setae on inner plate (with five plumose setae); inner plate of maxilla II with four plumose facial setae in an oblique row (with five plumose setae); inner plate of maxilliped with three stout apical spines, two serrated setae, and five plumose setae (with five simple strong apical setae and nine plumose setae); epimeral plate II with two spines on distal margin (with one seta).

The new species resembles Pseudocrangonyx gudariensis Tomikawa & Sato, 2016 in epimeral plate I without armature on distal margin; urosomite III dorsal margin without armature. It can be distinguished from Pseudocrangonyx gudariensis Tomikawa & Sato, 2016 by the following characters ( Pseudocrangonyx gudariensis in parentheses): accessory flagellum of antenna I subequal to the first article of primary flagellum (longer); antenna II of female with calceoli (absent); mandible spine row with five serrated spines (with 2-3 weakly pectinate setae); maxilla I with four plumose setae on inner plate (with three plumose setae); inner plate of maxilla II with four plumose facial setae in an oblique row (with three plumose setae); inner plate of maxilliped with three stout apical spines, two serrated setae, and five plumose setae (with three apical and two subapical robust setae); terminal article of uropod III outer ramus a little shorter than adjacent spines (longer); epimeral plates II and III with two spines on distal margins (with one seta); telson of male cleft 0.24 of its length (0.08).

The new species is also similar to Pseudocrangonyx holsingeri Sidorov & Gontcharov, 2013 in the armature of gnathopod I and II and pereopods III–VII; epimeral plate I without armature on distal margin; both rami of pleopods with more than five articles. It differs from Pseudocrangonyx holsingeri Sidorov & Gontcharov, 2013 by the following characters ( Pseudocrangonyx holsingeri in parentheses): accessory flagellum of antenna I subequal to the first article of primary flagellum (longer); inner plate of maxilliped with three stout apical spines, two serrated setae, and five plumose setae (with two apical and three sub-apical setae); epimeral plate III with two spines on distal margin (with three setae); uropod I peduncle with one basofacial spine (with two basofacial spines in female); uropod III peduncle with one dorsal and three ventral robust spines (with two sets of stiff setae on distal margins).

Distinguishing features of all the 22 species of genus Pseudocrangonyx can be found in the key below.