Nicippe recticaudata, Matsukami, Sachi, Nakano, Takafumi & Tomikawa, Ko, 2017

Matsukami, Sachi, Nakano, Takafumi & Tomikawa, Ko, 2017, A new species of the genus Nicippe from Japan (Crustacea, Amphipoda, Pardaliscidae), ZooKeys 668, pp. 33-47 : 34-35

Nicippe recticaudata sp. n. Figures 1, 2, 3, 4, 5, 6, 7

Nicippe tumida : Ren 2012: 349-351, fig. 154.

Material examined.

Holotype: male (8.4 mm), NSMT-Cr 25456 (Fig. 1A), off Cape Toi (31°14.54'N, 131°32.20' E– 31°14.94'N, 131°31.46'E; 265-367 m deep), Japan, collected by K. Tomikawa, 29 May 2006. Paratypes: female (8.5 mm), NSMT-Cr 25457 (Fig. 1B), male (8.5 mm), NSMT-Cr 25458, male (10.4 mm), KUZ Z1807, male (6.8 mm), KUZ Z1808, data same as for holotype.

Diagnosis.

Dorsal margin of urosomite 1 with 2 pointed teeth; posterior margin of merus of pereopod 4 with 5-6 setae; anterior margin of merus of pereopod 5 with 9-10 setae; telson with straight inner margin, tapering proximally.

Description of male

(holotype, NSMT-Cr 25456). Head (Fig. 2A) without any trace of eyes or ommatidia; rostrum pointed; lateral cephalic corners angularly produced. Pereon segments 1-4 subequal in length, slightly shorter than segment 5; segment 6-7 longest, about 1.3 times length of previous segment. Pleonites 1-3 in length ratio of 1.0: 1.3: 1.3. Posteroventral corners of epimeral plates 1-3 each with prominent small tooth (Fig. 4 G–I); ventral submargins of epimeral plates 2 and 3 with 2 setae, respectively. Urosomites 1-3 in length ratio of 1.0: 1.0: 1.2; urosomite 1 with 2 pointed teeth extending beyond posterior margin of its segment (Fig. 4J); urosomites 2 and 3 dorsally smooth.

Antenna 1 (Fig. 2B): length 0.6 × body length; peduncular articles 1-3 in length ratio of 1.0: 0.6: 0.3; posterodistal corner of peduncular article 1 with 2 long setae; accessory flagellum 3-articulate, article 1 long, length 4.8 × width; primary flagellum 38-articulate, length of article 1 longer than peduncular articles 2 and 3 combined, callynophore weakly developed.

Antenna 2 (Fig. 2C): length 0.9 × antenna 1, peduncular articles 3-5 in length ratio of 1.0: 1.1: 1.1; flagellum 29-articulate.

Mouthparts. Upper lip (Fig. 2D) with shallowly concave ventral margin, lobes symmetric. Mandibles (Fig. 2 E–G): slightly asymmetric, incisor margins broad, straight, anterodosal corner rounded, anteroventral corner with a strong tooth; left lacinia mobilis (Fig. 2F) broad, about 0.8 × length of incisor, multi-dentate; right incisor (Fig. 2G) with 2 teeth on proximal to anterodorsal corner; right lacinia absent; accessory setal row of left and right mandibles each with 2 robust setae, and a proximal tuft of seta; molar absent; mandibular palp 3-articulate with length ratio of 1.0: 3.6: 2.7, article 2 with 12 setae, article 3 with 5 posterolateral and 3 apical setae. Lower lip (Fig. 2H) with broad outer lobes, inner lobes coalesced. Maxilla 1 (Fig. 2I) with inner and outer plate and palp; inner plate small with apical seta; outer plate subrectangular with 7 spine-teeth and 1 stout plumose seta, the lateral one strongest and longest; left and right palps symmetric, palp 2-articulate, article 1 lacking marginal setae, article 2 expanded distally, with 8 robust and 8 slender setae on its apical margin. Maxilla 2 (Fig. 2J) with moderately slender inner and outer plates; inner plate bearing row of plumose setae on apical to medial margin; outer plate slightly longer than inner plate with apical plumose setae. Maxilliped (Fig. 2K) with inner and outer plates and palp; inner plate not reaching base of palp, with long plumose seta and short simple seta apically; outer plate narrowly rounded, reaching base of article 2 of palp, with setae along apical to medial margin; palp raptorial, 4-articulate, long, article 2 longest with inner marginal rows of setae, article 3 covered with 4 clusters of setae, article 4 slender with serrate inner margin.

Gnathopod 1 (Fig. 3A): coxa ovate with seta on anterodistal corner; basis long, expanded distally, anterior margin straight, posterior margin arched; ischium short, triangular, subequal in length to merus; carpus with short rounded lobe ventrally with long setae; propodus oval, about as wide as carpus, palm straight with long setae; dactylus slender, slightly curved, inner margin smooth with tooth near the base.

Gnathopod 2 (Fig. 3B): coxa rounded with seta on anterodistal corner, posteroproximal part with setae; compared to that of gnathopod 1, basis longer, more slender and straighter; carpal lobe stronger; dactylus similar, slightly shorter.

Pereopod 3 (Fig. 3C): coxa quadrate, posterior margin with setae; basis long with small setae on anterior and posterior margins; merus with 8 setae on posterior margin, 7 facial setae, and a cluster of setae comprising 3 setae on posterodistal corner; carpus and propodus with plumose and simple setae on posterior margin, and laterofacial setae; dactylus slender and weakly curved, length 0.7 × propodus.

Pereopod 4 (Fig. 3D): coxa rounded, ventral and posterior margins with setae; basis long with setae on anterior and posterior margins; merus with 5-6 setae on posterior margin, 7 laterofacial setae, and a cluster of setae comprising 3 setae on posterodistal corner; carpus and propodus with plumose and simple setae on posterior margin, and laterofacial setae; dactylus slender and weakly curved, length 0.6 × propodus.

Pereopod 5 (Fig. 4A): coxa bilobate, anterior lobe stronger and slightly longer with seta on ventral margin; basis posterior margin slightly convex with 2 small setae, posteroventral corner subquadrate with 2 minute setae; merus, carpus, and propodus in length ratio of 1.0: 0.8: 0.9; merus with 9 setae on anterior margin and 5 setae on submargin, anterodistal corner with 1 long and 3 relatively short setae; dactylus slender and almost straight, longer than on pereopods 3-4, 0.76 × length of propodus.

Pereopod 6 (Fig. 4B): coxa shallowly bilobate, anterior lobe slightly stronger; basis posterior margin slightly convex without setae, posteroventral corner subquadrate with seta.

Pereopod 7 (Fig. 4C): coxa ventral margin shallowly concave, anterior margin and ventral submargin each with 2 setae; basis expanded more strongly than pereopods 5-6, distally tapering, posteroproximal margin convex, anterodistal margin with setae, posteroventral corner slightly produced into a small rounded lobe, armed with 2 long setae.

Coxal gills on gnathopod 2 and pereopods 3-5 broad, longer than those of bases; gill on pereopod 6 ovate, length 0.5 × basis; gill on pereopod 7 slender, length 0.2 × basis.

Pleopods 1-3 (Fig. 4D) each with paired retinacula (Fig. 4E) on inner distal margin of peduncle, bifid setae (clothes-pin setae) (Fig. 4F) on inner basal margin of inner ramus; inner and outer rami of each pleopod consisting of 18 and 21 articles, respectively.

Uropods. Uropod 1 (Fig. 5A): peduncle slightly longer than rami, distolateral peduncular tooth very strong; outer ramus somewhat longer than inner ramus, outer and medial margins of outer ramus with 6 and 4 robust setae, respectively; outer and medial margins of inner ramus with 4 and 8 robust setae, respectively; both rami with stout setae apically. Uropod 2 (Fig. 5B): distolateral peduncular tooth short; outer ramus slightly longer than inner ramus, outer and medial margins with 6 and 7 robust setae, respectively; inner ramus with 6 outer and 4 medial robust setae, respectively; both rami with a stout seta apically. Uropod 3 (Fig. 5C): peduncle setose on outer margin, length 0.5 × outer ramus; outer ramus 1-articulate, somewhat longer than inner ramus; outer and medial margins of inner ramus each with plumose seta; medial margins of both rami with traces of setae.

Telson (Fig. 5D) length 2.0 × width, cleft for 88% of length in V-shape with straight inner margins of incision, each lobe with 4 setae laterally; apex of each lobe incised, lateral part of apex slightly longer than medial part, with small robust seta, lobes slightly tapering distally.

Description of female

(paratype, NSMT-Cr 25457).Antenna 1 (Fig. 6A): length 0.6 × body length; article 1 of accessory flagellum short, length 2.4 × width; primary flagellum 43-articulate, callynophore weakly developed.

Antenna 2 (Fig. 6B): length 0.7 × antenna 1; flagellum 18-articulate.

Gnathopod 1 (Fig. 6C): anterior and posterior submargins of basis with many setae.

Gnathopod 2 (Fig. 6D): anterior margin and posterior submargin of basis with many setae.

Pereopods 6 and 7 (Fig. 7A, B): similar to those of holotype; merus–propodus slender, with setae on anterior and posterior margins, and facial setae; dactylus slender, slightly curved inward.

Telson (Fig. 7C): length 1.9 × width, cleft for 90% of length, incision wider than that of male, each lobe with 6-7 setae laterally.

Variation.

Callynophore on antenna 1 well developed (3 males, NMST-Cr 25458, KUZ Z1807, Z1808); peduncular article 5 of antenna 2 longer than 1.5 × article 4 (3 males, NMST-Cr 25458, KUZ Z1807, Z1808); posterior margin of merus of pereopod 4 with 5-6 setae; anterior margin of merus of pereopod 5 with 9-11 setae.

Coloration.

Color in life unknown; faded in preservative (Fig. 1).

Etymology.

The specific name is a compound adjective derived from the Latin words rectus, and caudatus referring to the fact that the inner margin of the telson of this species is straight, a diagnostic character of the species.

Sequences and COI genetic distances.

In total nine nucleotide sequences were determined: holotype (NSMT-Cr 25456), four sequences, 28S (LC214961; 1336 bp), H3 (LC214963; 328 bp), COI (LC214958; 658 bp), and 16S (LC214956; 407 bp); paratype (NSMT-Cr 25457), four sequences, 28S (LC214962; 1336 bp), H3 (LC214964; 328 bp), COI (LC214959; 658 bp), and 16S (LC214957; 407 bp); and paratype (KUZ Z1807), one sequence, COI (LC214960; 658 bp).

The obtained three COI sequences (LC214958-LC214960) were completely identical to each other. Based on the 651 bp aligned sequences, the COI uncorrected p-distance between N. recticaudata and the eastern North Pacific " N. tumida " was 17.1%.

Remarks.

Although the present specimens showed two characteristics in the degree of callynophore of male antenna 1 and the length of peduncular article 5 of male antenna 2, the obtained genetic data revealed that these morphological variants (specimens with strongly developed callynophore and long peduncular article 5 of antenna 2, e.g., KUZ Z1807 vs specimens with weakly developed callynophore and short peduncular article 5 of antenna 2, e.g., NSMT-Cr 25456) shared completely identical COI sequences, and thus they were identified as the same species. The character states of the well developed callynophore of antenna 1 and the elongate peduncular article 5 of antenna 2 were observed only in males of N. recticaudata . Males with these characteristics might be regarded as fully mature individuals.

According to the conventional classification of Nicippe species, this species would be identified as N. tumida based on the possession of the two-dentate posterior margin of urosomite 1. However, Nicippe recticaudata clearly differs from the “true” N. tumida defined by Bruzelius (1859) and Sars (1895) in the following three characteristics (character states of N. tumida in parentheses): posterior margin of merus of pereopods 4 with 5-6 setae (more than 10); anterior margin of merus of pereopod 5 with 9-10 setae (more than 20); and telson with straight inner margin, tapering proximally (sinuous inner margin, weakly expanding proximally). Moreover, the calculated COI genetic distance (17.1%) between N. recticaudata specimens and the N. tumida sample from California (Northeastern Pacific) revealed that the new species is genetically diverged from the Californian population of N. tumida ; 3.5-4% COI distances have been proposed as the threshold for amphipod species discrimination ( Witt et al. 2006; Rock et al. 2007; Hou et al. 2009). The N. tumida individuals inhabiting Californian waters were once reported to possess the morphological characteristics resembling those of N. recticaudata ( Barnard 1959). Contrary to their morphological similarities, therefore, the present COI data highlighted that the population from Northwestern Pacific ( N. recticaudata ), and that inhabiting Northeastern Pacific (" N. tumida " in Californian waters) are different species. In summary, the present tumida -like Japanese population of Nicippe is considered as distinctive, and thus was described as a new species of the genus.

A Nicippe specimen identified as N. tumida was recorded from the East China Sea ( Ren 2012). However, its description as well as figures clearly shows the diagnostic characteristics of N. recticaudata , and thus the Chinese sample in Ren (2012) definitely belongs to the present new species. As well, N. tumida has been recorded from around the Japanese Archipelago, e.g., from Sea of Japan and Sea of Okhotsk ( Gurjanova 1951; Bulycheva 1957). Because these previous records lacked the detailed descriptions related to the diagnostic characters of N. recticaudata , their identities remain unclear. A world-wide systematic revision is essential to elucidate the cryptic species diversity in N. tumida .