A new species of Nicippe from the Bering Sea (Crustacea, Amphipoda, Pardaliscidae), with a redescription of N. tumida

Abstract A new pardaliscid amphipod, Nicippe beringensis, is described from the Bering Sea at depths between 520 and 536 m, and N. tumida Bruzelius, 1859 is redescribed based on specimens from Fredrikshald, Norway, near the species’ type locality. Nucleotide sequences of mitochondrial cytochrome c oxidase subunit I (COI) from the holotype and a paratype of N. beringensissp. nov. are reported. While N. beringensissp. nov. is similar to N. tumida, it differs from the latter in having an asetose palp article 1 of maxilla 1, a gnathopod 1 coxa with a straight distal edge, and in the posterior margin of the basis of gnathopods 1 and 2, and pereopod 3, being heavily setose in females. A key to species of Nicippe is provided.


Introduction
The genus Nicippe Bruzelius, 1859 has been recorded from littoral to deep-sea marine environments; it currently comprises five species: N. tumida Bruzelius, 1859, N. buchi Andres, 1975, N. recticaudata Matsukami, Nakano & Tomikawa, 2017, N. rogeri Lörz al. (2014. The primer set for the cytochrome c oxidase subunit I (COI) gene (LCO1490 andHCO2198;Folmer et al. 1994) was used for PCR and cycle sequencing reactions. PCR and sequencing followed methods detailed in Tomikawa et al. (2017). The DNA sequence has been deposited with the International Nucleotide Sequence Database Collaboration (INSDC) through the DNA Data Bank of Japan (DDBJ).
Mouthparts. Upper lip ( Fig. 2D) with weakly convex ventral margin, bearing fine setae. Mandibles (Fig. 2E, F): slightly asymmetric, incisor margins broad, an- teroventral corner with a strong tooth; left lacinia mobilis ( Fig. 2E) broad, about 0.8 times as long as incisor, multi-dentate; right incisor ( Fig. 2F) with 2 teeth on proximal to anterodorsal corner; right lacinia absent; accessory setal row of left and right mandibles with 2 robust setae, respectively, and a proximal tuft of seta; molar absent; mandibular palp 3-articulate with length ratio of 1.0 : 3.3 : 2.6, article 2 with 5 marginal and 12 submarginal posterolateral setae, article 3 with 7 posterolateral and 3 apical setae. Lower lip ( Fig. 2G) with broad outer lobes, inner lobes coalesced. Maxilla 1 (Fig. 2H) with inner and outer plates and palp; inner plate small with apical plumose seta; outer plate subrectangular with 8 apical robust setae, the lateral one strongest and longest; palp 2-articulate, article 1 lacking marginal setae, article 2 expanded distally with robust and slender setae. Maxilla 2 ( Fig. 2I) with inner plate bearing row of 5 plumose setae on medial margin and 3 apical plumose setae; outer plate slightly longer than inner plate with 3 apical plumose setae. Maxilliped ( Fig.  3A) with inner and outer plates and palp; inner plate not reaching base of palp, with long plumose apical seta and short weakly plumose subapical seta; outer plate narrow, reaching base of article 2 of palp, with setae along apical to medial margin; palp 4-articulate, long, article 2 longest with inner marginal rows of setae, article 3 with clusters of setae on dorsal and ventral faces and inner marginal setae, article 4 slender with serrate inner margin.
Gnathopod 1 (Fig. 3B): coxa short, length 1.3 times of width, distal edge straight; basis long, expanded distally, anterior margin flat, posterior margin arched with numerous setae in row; ischium short, subquadrate, 0.7 times as long as merus; posterior margin of merus with setae; carpus with rounded lobe ventrally with long setae, length 1.1 times of width; propodus oval, length 1.8 times as long as carpus, palm weakly convex with long setae; dactylus slender, slightly curved, posterior margin smooth with tooth near the base.
Gnathopod 2 (Fig. 3C): coxa rounded ventrally, posterior margin and medial face with setae; compared to that of gnathopod 1, basis longer and more slender; carpus ventrally more strongly produced, length 1.3 times of width; dactylus similar to that of gnathopod 1.
Uropods. Uropod 1 (Fig. 4I): peduncle longer than rami, with 5 basofacial setae, distolateral peduncular spine very strong; inner ramus subequal to outer ramus in length, medial and lateral margins with 9 and 7 robust setae, respectively; outer ramus with 7 robust setae on medial and lateral margins, respectively; both rami with stout setae apically. Uropod 2 (Fig. 4J): peduncle slightly shorter than rami, with long stout setae on lateral margin, distolateral peduncular spine short; inner ramus slightly longer than outer ramus, with 7 and 9 robust setae on medial and lateral margins, respectively; outer ramus with 8 and 7 robust setae on medial and lateral margins, respectively; both rami each with stout seta apically. Uropod 3 (Fig. 4K): peduncle strongly setose on lateral face; both rami almost equal in length, medial margins of inner and outer rami with long plumose setae. Telson (Fig. 4L) length 2.2 times of width, cleft for 89% of length in U-shape with weakly curved margins of incision; apex of each lobe incised, lateral part of apex slightly longer than medial part, with small robust seta.
Gnathopods 1 and 2: bases with a few setae on their posterior margins. Etymology. The specific name is an adjective derived from its type locality, the Bering Sea.

Sequences and COI genetic distances.
A single nucleotide sequence was obtained from each specimen of the holotype, NSMT-Cr 27383 (LC511042; 615 bp) and a paratype, NSMT-Cr 27384 (LC511043; 658 bp). Based on the 615 bp aligned sequences, the uncorrected p-distances between these two specimens is 0.2%.
Remarks. Though the holotype and paratypes were obtained from slightly different localities, they differ in no appreciable morphological character or state. The pairwise sequence divergence of COI between the holotype and paratype, 0.2%, is considerably less than that of interspecific distances between other amphipod taxa, 3.5-4.0% (Witt et al. 2006;Rock et al. 2007;Hou et al. 2009). Accordingly, we consider these two specimens to be conspecific.
Remarks. Though the present specimens agree with the original description of N. tumida (Bruzelius 1859), there are some differences between them. Pereopod 7 bears long plumose setae on the posterior margin of the basis in the original description, whereas the present specimens lack these setae. We confirmed that these plumose setae are fragile and easily broken off during handling for the observation of N. beringensis. Thus, these setae may have been broken off in the present specimens. The telson of the present material takes on the almost parallel shape at either inner margin. Judging from the illustration of the original description, the telson has a wide cleft distally and its inner margins are not parallel. It is a highly likely that the telson was erroneously drawn because Bruzelius' illustrations were simplified and there are some unreasonable aspects, e.g. the shape of coxae of pereopods 5-7 and epimeral plates. To confirm these dubious features as well as the telson shape, examination of the type material is needed. In this study, we could not access the type materials of N. tumida. Unfortunately, it is likely that the type specimens are lost.