Nuuanu paracyclodactyla, Jung & Yoon, 2015

Jung, Tae Won & Yoon, Seong Myeong, 2015, New records of Nuuanuidae (Crustacea: Amphipoda: Senticaudata) from Korean waters, with descriptions of one new genus and two new species, Journal of Natural History 50, pp. 1045-1072 : 1059-1071

Nuuanu paracyclodactyla sp. nov.

(Korean Name: Keun-son-ga-rak-nu-a-nu-yeop-sae-u, new)

( Figures 6 – 10 )

Type material

Holotype. Adult male, 9.3 mm, dissected on slide glasses, NIBRIV0000305386, Dumi Island , Dumi-ri , Yokji-myeon, Tongyeong-si, Gyeongsangnam-do, Korea (34°41′23″N, 128°11′42″E), 5 April 2010, SCUBA diving (depth 15 m), collected by TW Jung.

Allotype. Adult female, 6.5 mm, dissected on slide glasses, NIBRIV0000305387, collection details same as holotype.

Paratypes. Adult 2 females, 5.7 and 5.2 mm, not dissected, collection details same as holotype.

Description

Holotype male. Head ( Figure 6A ), rostrum minute; anterior cephalic lobe weakly sinuated; antennal sinus not developed and forming small notch anteriorly; eyes circular and weakly developed.

Antenna 1 ( Figure 6A, B ) longer than antenna 2; peduncular articles 1 – 3 in length ratio of 1.00: 1.04: 0.43; peduncular article 1 somewhat convex and robust, posterodistal corner with spine; peduncular articles 2 and 3 slender; accessory flagellum 4-articulate, distal margin of each article with several setae; flagellum longer than peduncular articles 1 – 3 combined and 41-articulate, each article with several setae distally; calceoli, aesthetasc absent.

Antenna 2 ( Figure 6A, C, D ) about half as long as antenna 1; gland cone acute; peduncular article 4 slightly dilated posterodistally, posteroproximal margin with four split ended setae; flagellum slightly shorter than peduncular articles 4 and 5 combined and 25-articulate, distolateral margin of each article with four or five setae and distomedial margins more pubescent.

Upper lip ( Figure 6E ) obtuse triangular, apical margin convex with fine setae distally.

Lower lip ( Figure 6F ) with well-developed mandibular processes; outer lobe round apically with several stout and curved setae; inner lobe weak.

Right mandible ( Figure 6K, L ), incisor 5-dentate; lacinia mobilis bifid with several teeth; accessory setal row with 11 dentate setae; molar processes triturative with long plumose seta and short setae; palp slender and tri-articulate, articles 1 – 3 in length ratio of 1.00: 2.08: 2.20, article 2 with 3 setae near distal corner, article 3 weakly falcate and distal two-thirds of inner margin lined with short setae, apex with three long setae.

Left mandible ( Figure 6J ), incisor 6-dentate; lacinia mobilis 4-dentate; accessory setal row with 12 dentate setae; molar processes and palp similar to those of right mandible.

Maxilla 1 ( Figure 6G, H ), inner plate, apex produced, inner margin lined with long plumose and normal setae; outer plate, apex lined with nine dentate robust spines; palp bi-articulate, article 1 short and distal corner obliquely truncated, article 2 somewhat dilated mesially with eight spines apically and four plumose setae subapically.

Maxilla 2 ( Figure 6I ), inner plate, surface with oblique row of 24 plumose setae, distal half of inner margin with plumose setae, apical margin with apical and subapical rows of setae; outer plate also with rows apically and subapically.

Maxilliped ( Figure 6M ), inner plate rectangular with three stout apical spines and many plumose setae on apical, subapical and inner margins; outer plate, lateral margin round and slightly expanded, medial and distal margins lined with 13 stout pectinate spines that successively increasing in length; palp 4-articulate, article 1 short and obliquely truncated distally, article 2 slightly dilated, and inner margin lined with numerous long setae, inner margin of article 3 hump-like mesially bearing several setae and subdistal margin lined with row of numerous spinules, article 4 falcate with row of spinules on inner margin and stout spine apically.

Gnathopod 1 ( Figure 7A, B ); coxa subrectangular, about twice as long as wide, anterior and ventral margins lined with minute setae, posteroventral corner weakly dilated backward with small notch ventrally bearing small seta; basis linear, anterior margin lined with several short and long setae, posterior margin with six long mesial setae, posterodistal margin shallowly convex with minute seta distally; ischium lobate anteriorly with group of setae near posterodistal corner; merus, distal half of posterior margin round and lined with several setae, distal corner weakly produced; carpus elongate, slightly shorter than basis, anterior margin bare, anterodistal margin with row of several long setae, posterior margin weakly sinuated and lined with several groups of pectinate setae, lateral and medial surfaces with several oblique rows of several setae; propodus little expanded distally and slightly longer than half of carpus, distal half of anterior and posterior margins with several setae, posterodistal surface with row of several setae; palm weakly oblique, lined with small setae; dactylus fitting palm, inner margin serrated.

Gnathopod 2 ( Figure 7C, D ) extensively stout, especially propodus and dactylus enlarged remarkably; coxa longer than that of gnathopod 1, margins smooth, anterior margin swollen, ventral margin lined with minute setae and posteroventral corner with small notch bearing small seta; basis trigonal prism-shaped and anterior surface fitting proximal half of propodus, anterolateral margin with several setae and anteromedial margin bare, posterior margin with group of three long mesial setae; ischium, anterior surface forming groove, posterodistal corner with pair of minute setae; merus weakly dilated posterodistally with minute seta; carpus short and drastically expanded distally; propodus robust and extremely enlarged, anterior margin convex and weakly angulate mesially, posterior margin with notch mesially and distal half with five groups of short setules; palm, defining corner concave, distal two-thirds lined with five protrusions, each bearing one spine; respectively; dactylus cylindrical, gradually dilated, about two-thirds of propodus in length, apical margin smooth.

Pereopod 3 ( Figure 7E ), coxa similar but shorter than that of gnathopod 2; basis slender and slightly curved, anterior and posterior margins lined with minute and several long setae, anterodistal corner weakly lobate; ischium with small anterior lobe and pair of minute setae; merus trapezoidal, anterior margin weakly expanded and distal corner produced with pair of small setae; carpus shorter than merus, anterior margin a little swollen, posterior margin linear and lined with several paired and single spines; propodus shorter than carpus, anterior margin bare and distal corner with setae, posterior margin lined with seven pairs of spines; dactylus, anteroproximal margin with penicillate seta, inner margin with seta distally, distolateral margin with setae, unguis short and curved.

Pereopod 4 ( Figure 7F ) similar in size and shape to pereopod 3 except for larger coxa bearing slightly expanded and produced posteromesial margin, and small notch on anteroventral margin absent.

Pereopod 5 ( Figure 8A, B ), coxa subquadrate, ventral margin equilobate, each lobe slightly dilated posteroventrally; basis, anterior margin swollen and lined with several stout spines, posterior margin weakly serrate and lined with minute setae, posterodistal half somewhat concave and distal corner angulate; ischium subquadrate, posterior lobe small; merus, anterior margin with mesial spine and distal corner with hook-shaped projection bearing pair of unequal spines, posterior margin expanded distally and distal corner with pair of unequal stout spines, distal margin concave; carpus rectangular, anterior margin lined with 1-2-4-1 spines in formula, anterodistal and posterodistal corners with group of spines, respectively; propodus stout and shorter than carpus, anterior margin lined with 1-1-2-3-5 spines in formula from proximal to distal, anterodistal corner with pair of locking spines; posterodistal end blunt with three stout spines and several setae; dactylus, anteroproximal margin with penicillate seta, inner margin pectinated with seta distally, distolateral margin with setae, unguis short and curved.

Pereopod 6 ( Figure 8C, D ), coxa bilobate, anterior lobe smaller and produced ventrally, posterior lobe dilated posteroventrally; basis larger than that of pereopod 5, anterior margin convex but not more swollen than that of pereopod 5 mesially and lined with stout spines, posterior margin convex, weakly serrated and lined with minute setae; ischium subquadrate and posterior lobe small; merus, anterior margin with mesial spine and distal corner with hook-shaped projection bearing pair of unequal spines, posterior margin expanded distally with stout spine mesially and distal corner with pair of unequal stout spines, distal margin concave; carpus quadrate, anterior margin with 1-1-1-2-5-1-2 spines in formula from proximal to distal, posterior margin bare and distal corner with group of spines; propodus stout and shorter than carpus, anterior margin with spines in formula 2-2-3-4 from proximal to distal, posterodistal end blunt with group of several spines and setae; dactylus, anteroproximal margin with penicillate seta, inner margin pectinated with seta distally, distolateral margin with setae, unguis short and curved.

Pereopod 7 ( Figure 8E, F ), coxa unilobate; posteroventral margin round, weakly serrated and lined with minute setae; basis, anterior margin convex and lined with several spines, posterior margin largely expanded backward, serrated and lined with minute setae, posteromesial corner somewhat angulate; ischium subquadrate and posterior lobe small; ischium subquadrate and posterior lobe small; merus, anterior margin with one spine and one group of three medial spines, anterodistal corner with hookshaped projection bearing group of four spines, posterior margin expanded mesially with two stout spines, posterodistal corner produced with pair of unequal spines, distal margin concave; carpus quadrate and little wider distally, anterior margin with 2-4-5-2 spines in formula from proximal to distal, anterodistal corner with group of seven spines, posterior margin bare, posterodistal corner with pair of spines; propodus stout and shorter than carpus, anterior margin with 2-3-4-4 spines in formula from proximal to distal, anterodistal corner with pair of spines, posterior margin bare, posterodistal end blunt with stout several spines and setae, anterior margin with 2-3-4-4 spines in formula from proximal to distal, anterodistal corner with pair of spines, posterodistal end blunt with several stout spines and setae; dactylus, anteroproximal margin with penicillate seta, inner margin pectinated with seta distally, distolateral margin with setae, unguis short and curved.

Pleon ( Figure 9A, B ), dorsal keel very weak; pleonal epimeron 1 subquadrate, posteroventral corner weakly notched; pleonal epimera 2 and 3 subquadrate; each posterior margin feebly serrated and lined with minute setae.

Pleopod 1 ( Figure 9G ), peduncle rectangular with five long setae proximally, lateral margin pubescent, mediodistal margin with group of four retinaculae; rami longer than peduncle, inner ramus slightly shorter than outer.

Pleopod 2 ( Figure 9H, I ) similar to pleopod 1.

Pleopod 3 ( Figure 9J, K ), peduncle rectangular, but outer distolateral corner dilated with four plumose setae.

Urosome ( Figure 9A ) diminished but not coalesced; dorsal keel very weak; urosomite 2 with two dorsal spines; urosomite 3 with two small lobes and two spines on dorsal margin.

Uropod 1 ( Figure 9C ), peduncle longer than rami, dorsolateral margin lined with three spines and one stout distal spine, dorsomedial margin lined with five spines and one stout distal spine; each ramus shorter than peduncle; outer ramus, dorsal margin with four lateral and two medial spines, apex with three short and two stout spines; inner ramus, dorsal margin pectinate and with several small spines, apex with three small spines and one stout spine.

Uropod 2 ( Figure 9D ) stout and shorter than uropod 1; peduncle, distal corner of dorsolateral margin with short spine and seta, distal corner of dorsomedial margin with stout spine; each ramus subequal to ventral margin of peduncle; outer ramus with three dorsolateral and five dorsomedial spines, apex with four short spines and one stout spine; inner ramus with six spines dorsally, apex with four short spines and one stout spine.

Uropod 3 ( Figure 9E ) biramus; peduncle oval and shorter than that of uropod 2; medial margin with one and pair of distal spines and forming ridge distally that bears inner ramus, lateral margin with one mesial and pair of distal spines; inner ramus triangular, about half of inner ramus, apex with small distal spine; outer ramus biarticulate, proximal article gradually diminished in width with pair of spines distally, distal article very reduced with apical spine.

Telson ( Figure 9F ) trapezoidal, deeply cleft to near base, each apical corner with pair of setules.

Allotype female. Gnathopod 1 ( Figure 10F, G ) similar to that of male except for more dilated posteroventral corner of coxa.

Gnathopod 2 ( Figure 10H, I ) not enlarged, slightly larger than gnathopod 1; propodus longer than carpus and gradually diminished in width; palm distinct and oblique; dactylus short.

Coxal gills ( Figure 10F – J ) suboval, that of pereopod 4 largest and that of pereopod 3 smallest.

All oostegites slender ( Figure 10J – M ).

Etymology

The composite epithet of the specific name, paracyclodactyla , is a combination of the Greek prefix para- and the specific name of Gammarella cyclodactyla ( Hirayama, 1978) , which means ‘ near cyclodactyla’. This name refers to the close resemblance to G. cyclodactyla .

Remarks

Gammarella cyclodactyla ( Hirayama, 1978) has very peculiar shapes of the propodus and dactylus on the gnathopod 2 in mature males, and this has been known as a unique characteristic feature of this species until now. However, this new species, Nuuanu paracyclodactyla closely resembles Gammarella cyclodactyla in the following morphological characters: the remarkably enlarged propodus and dactylus and cylindrical shape of dactylus on gnathopod 2 in mature males, the small protrusion of posterior margin of coxa 4, the lobations of basis on pereopods 5 and 7, and the overall shapes of uropods 1 – 3 and pattern of dorsal spines of peduncle. Nonetheless, N. paracyclodactyla is easily distinguished from G. cyclodactyla in that the well-developed dorsal keels from pleonite 1 to urosomite 2 of G. cyclodactyla are absent in this new species. Lowry and Watson (2002) mentioned that the status of dorsal keels from pleonite 1 to urosomite 2 is the character state that enables us to discriminate between the two genera, Nuuanu and Gammarella , and this means that the developed dorsal keel from pleonite 1 to urosomite 2 is absent in all species of the genus Nuuanu . Hence, the absence of this characteristic feature in N. paracyclodactyla sp. nov. can now enable the ranking of this as a new species despite the similar shape of gnathopod 2 in mature males of the two species. This new species also shows other differences from G. cyclodactyla as follows: the mesial spines of posterior margin of peduncular article 1 on antenna 1 and of anterior margin of peduncular article 4 on antenna 2 are absent in N. paracyclodactyla ; the number of apical spines on outer plate of maxilla 2 is 10 in N. paracyclodactyla , but that of G. cyclodactyla is 11; the accessory flagellum is 4-articulate in N. paracyclodactyla , but that of G. cyclodactyla is 5-articulate; anterodistal and posterodistal corners of basis and posterodistal corner of ischium have small spine or paired small spines in G. cyclodactyla , but those of N. paracyclodactyla are absent; the distal half of posterior margin of basis on pereopod 6 is slightly convex in G. cyclodactyla ; the dorsal spots bearing some grooves and hollows on pleonites 1 – 3 and urosomite 1 are absent; all pleonal epimera of the new species have acute posteroventral corners, but those of G. cyclodactyla just show that on the pleonal epimeron 3; the telson is not fully cleft in this new species ( Table 1).

Disclosure statement

No potential conflict of interest was reported by the authors.

Funding

This study was supported by the National Institute of Biological Resources of Korea as part of the ‘ Survey of indigenous biological resources of Korea (NIBR NO. 2014-01-001) ’ and partly supported by the National Marine Biodiversity Institute of Korea as a part of the ‘ Study on the conservation plan for managed marine organism (2015 M00100 ) ’.

ORCID

Tae Won Jung http://orcid.org/0000-0002-4879-5346

Seong Myeong Yoon http://orcid.org/0000-0002-3246-3021

Figures

Figure 6. Nuuanu paracyclodactyla sp. nov., holotype, male. (A) Head, antennae 1 and 2; (B) antenna 2; (C) accessory flagellum; (D) medial surface of flagellum on antenna 2; (E) upper lip; (F) lower lip; (G) maxilla 1; (H) apical spines of outer plate on maxilla 1; (I) maxilla 2; (J) left mandible; (K, L) right mandible; (M) maxilliped.

Figure 7. Nuuanu paracyclodactyla sp. nov., holotype, male. (A) Gnathopod 1; (B) coxa 1; (C) gnathopod 2; (D) coxa 2; (E) pereopod 3; (F) pereopod 4.

Figure 8. Nuuanu paracyclodactyla sp. nov., holotype, male. (A) Pereopod 5; (B) dactylus of pereopod 5; (C) pereopod 6; (D) dactylus of pereopod 6; (E) pereopod 7; (F) dactylus of pereopod 7.

Figure 9. Nuuanu paracyclodactyla sp. nov., holotype, male. (A) Pleon and urosome, lateral view; (B) posterior margins of pleonal epimera; (C) uropod 1; (D) uropod 2; (E) uropod 3; (F) telson; (G) pleopod 1; (H) pleopod 2; (I) retinaculae of pleopod 2; (J) pleopod 3; (K) retinaculae of pleopod 3.

Figure 10. Nuuanu paracyclodactyla sp. nov., holotype, male (A–E) and allotype, female (F–M). (A–E) Gills of gnathopod 2–pereopod 6; (F) gnathopod 1; (G) palm of gnathopod 1; (H) gnathopod 2; (I) palm of gnathopod 2; (J–M) oostegites of gnathopod 2–pereopod 5.