Gammarus baengnyeongensis, Kwon & Kim & Heo & Kim, 2020

Kwon, So-Yeon, Kim, Min-Seop, Heo, Jun-Haeng & Kim, Young-Hyo, 2020, A new Gammarus species (Crustacea, Amphipoda, Gammaridae) from Northwestern Islands, South Korea, Zootaxa 4896 (4), pp. 535-546 : 537-543

publication ID	https://doi.org/ 10.11646/zootaxa.4896.4.5
publication LSID	lsid:zoobank.org:pub:8F11E9BD-CA99-4999-8D99-27554C95EAB2
DOI	https://doi.org/10.5281/zenodo.4389309
persistent identifier	https://treatment.plazi.org/id/DB3B5361-FF8D-FF99-1EFF-FE5AFC19F84A
treatment provided by	Plazi
scientific name	Gammarus baengnyeongensis
status	sp. nov.

Treatment

Gammarus baengnyeongensis sp. nov

(Korean Name: Baek-ryeong-do-yeop-sae-u, new)

( Figs. 2–6 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 )

Type material. Holotype, adult male, 12.5mm, cat no. NIBRIV0000877256 , Yeonhwa-ri , Baengnyeongdo Island , Baengnyeong-myeon, Ongjin-gun, Incheon, South Korea, 37°55′37.5″N, 128°38′33.8″E, 14 July 2007, collected by Y.H. Kim. GoogleMaps

Paratypes: 30 ³ ( NIBRIV0000877257 ) , 20 ♀ ( NIBRIV0000877258 , NIBRIV0000877259 ); all other data same as the holotype. 5 ³ GoogleMaps , 15 ♀, Daecheong-ri , Daecheongdo Island , Daecheong-myeon, Ongjin-gun, Incheon, South Korea, 37°49'5.8"N, 124°41'13.2"E, 5 November 2009, collected by D.H. Ahn. GoogleMaps

Etymology. The species name is from the type locality, Baengnyeongdo Island located on the west coast of South Korea.

Description. Holotype adult male, 12.5 mm, cat no. NIBRIV0000877256.

Body ( Fig. 3A View FIGURE 3 ) about 12.5 mm long; head as long as wide, subequal in length to pereonites 1–2 combined, rostrum rounded, flat; eye small, subreniform, black in alcohol.

Antenna 1 ( Fig. 3B View FIGURE 3 ) about 0.4 times as long as body length; peduncular articles with tufts of setae distally; length ratio of peduncular articles 1–3= 1.00: 0.75: 0.46; flagellum 18-articulate, each article with short distal setae; accessory flagellum 6-articulate, subequal to flagellum articles 1–3 combined, each article with short distal setae, article 6 comparatively short.

Antenna 2 ( Fig. 3C View FIGURE 3 ) 0.75 times as long as antenna 1; length ratio of peduncular articles 3–5= 1.00: 2.91: 3.16; flagellum 10-articulate, articles 1–7 with a rounded calceoli dorsally.

Upper lip ( Fig. 3D View FIGURE 3 ) subrounded, convex, densely pubescent ventrally.

Lower lip ( Fig. 3E View FIGURE 3 ), inner lobe absent; outer lobe pubescent medially and apically, mandibular process short and blunt.

Left mandible ( Fig. 3F View FIGURE 3 ), incisor 5 dentate; lacinia mobilis with 4 blunt teeth setal row with 11 setae; molar triturative, with 1 pappose seta; mandibular palp, article 2 with 13 simple setae, distal article missing.

Right mandible ( Fig. 3G View FIGURE 3 ), incisor 4 dentate; lacinia mobilis trifurcate, with weak dentitions apically; setal row with 7 setae; mandibular palp well developed, article 2 with 2 A2-setae, 6 B2-setae, and 4 D2-setae; article 3 with 5 A3-setae, 3 B3-setae, 27 D3-setae, and 5 E3-setae.

Maxilla 1 ( Fig. 3H View FIGURE 3 ), inner plate subrectangular, with 15 plumose setae; outer plate with 11 dentate-spines apically; palp biarticulate, distal article with 4 slender spines apically and 5 subapical setae.

Maxilla 2 ( Fig. 3I View FIGURE 3 ) setose, inner plate with serrulate and plumose setae on inner margin, several serrulate and simple setae apically; outer plate slightly longer than inner plate, with stiff setae apically.

Maxilliped ( Fig. 3J View FIGURE 3 ), inner plate subrectangular, with 4 apical and 1 subapical spines; outer plate broad, with 12 blade spines medially and 10 simple setae apically; palp 4-articulate, article 1 unarmed, article 2 with numerous simple setae on inner margin and 2 tufts of a few simple setae on outer margin, article 3 elongate, with several pectinate and simple setae subapically, 2 dentate-spines apically.

Gnathopod 1 ( Fig. 4A View FIGURE 4 ) subchelate; coxa subquadrate, with 3 short setae anterodistally, and 1 short seta pos-terodistally; basis with long curved or 3 long pinnate setae posteriorly, several unequal simple setae anteriorly, 3 stiff cuspidate setae ventrodistally; carpus with several clusters of simple setae posteriorly and 5 stiff cuspidate setae distomedially; propodus subovate, narrowing distally, 1.37 times as long as carpus, with a row of simple setae ventrally, palm gently oblique, with 3 medial spines and 11 spines posteriorly; dactylus falcate, 0.73 times as long as propodus.

Gnathopod 2 ( Fig. 4B View FIGURE 4 ) similar to gnathopod 1; coxa subquadrate, width 0.46 times length, with 3 anterodistal setules, 1 posterodistal setule, and 3 unequal setae subposterodistally; basis subrectangular, narrowing proximally, with 8 long simple setae anteriorly and 4 cuspidate setae distally; carpus 0.63 times as long as basis, with 8 clusters of pinnate and simple setae posteriorly, and 3 clusters of simple setae anteriorly; propodus subchelate, 1.15 times as long as carpus, with 7 clusters of simple and pinnate setae posteriorly, 4 clusters of simple setae anteriorly, palm oblique, with 1 blunt medial spine and 4 small spines on palmar corner; dactylus falcate, 0.67 times as long as propodus.

Pereopod 3 ( Fig. 4C View FIGURE 4 ), coxa subrectangular, width 0.42 times length, with 3 anterodistal and 1 posterodistal setul; basis with 23 unequal simple setae posteriorly, 14 unequal simple setae anteriorly; merus elongate, with 9 clusters of simple setae posteriorly; carpus with unequal simple setae and 2 spines posteriorly, anterior margin unarmed; propodus more slender than and 1.20 times longer than carpus, with 6 spines and accompanied by setae along the posterior margin, and 5 setae anterodistally; dactylus with 1 short setae on hinge of the nail.

Pereopod 4 ( Fig. 4D View FIGURE 4 ) similar to pereopod 3, except coxa 4 with posteroproximal excavation and 6 posterodistal, 2 anterodistal setules; merus, carpus, and propodus with shorter setae than those of pereopod 3.

Pereopod 5 ( Fig. 4E View FIGURE 4 ), basis subovate, width 0.68 times length, posterior margin rounded, weakly serrate, with a row of marginal setules, anterior margin straight with 4 proximal setae, 4 spines accompanied by setules; merus, carpus, propodus setose, with a row of duad or triad spines on both margins.

Pereopod 6 ( Fig. 5A View FIGURE 5 ) similar to pereopod 5, except basis subrectangular.

Pereopod 7 ( Fig. 5B View FIGURE 5 ) similar to pereopod 6, except basis subquadrate, width 0.80 times length, slightly broader than that of pereopod 6 and slightly shorter than pereopod 6.

Urosomites 1–3 ( Fig. 5C View FIGURE 5 ) dorsally flat; urosomite 1 with 1–2–1 spines on dorsal margin from left to right; urosomite 2 with 2–2–2 spines; urosomite 3 with 1–0–1 spines on each side.

Uropod 1 ( Fig. 5D View FIGURE 5 ), peduncle subrectangular, 1.40 times longer than inner ramus, with a row of 6 dorsolateral and 3 dorsomedial spines; outer ramus subequal to inner one.

Uropod 2 ( Fig. 5E View FIGURE 5 ), peduncle 1.62 times longer than inner ramus, with a row of 4 dorsolateral and 5 dorsomedial spines; inner ramus with 1 spine on each margin, 3 apical spines; outer ramus with 1 lateral spine, 5 unequal apical spines, 1.27 times as long as inner one.

Uropod 3 ( Fig. 5F View FIGURE 5 ), peduncle short, 0.56 times as long as inner ramus, with 2 apical and 3 lateral spines on each margin; inner ramus with 2 spines and long simple setae apically; outer ramus biarticulate, 1.30 times longer than inner one, proximal article with 2 spines laterally, 4 spines and long simple setae distally, terminal article longer than adjacent spines; both rami surrounded by plumose setae.

Telson ( Fig. 5G View FIGURE 5 ) deeply cleft nearly to the base; each lobe with 2 spines accompanied by 8 simple setae apically, a tuft of four simple setae medially, two tufts of simple setae and a pair of penicillate setae laterally.

Paratype, adult female, body 12.3 mm ( Fig. 6A View FIGURE 6 ), cat no. NIBRIV0000877258.

Antenna 2 ( Fig. 6A View FIGURE 6 ) similar to that of male, except flagellum without calceoli.

Gnathopod 1 ( Fig. 6B View FIGURE 6 ) similar to that of male, except medial palmar spine lacking.

Gnathopod 2 ( Fig. 6C View FIGURE 6 ) similar to that of male, except medial palmar spine lacking.

Uropod 3 ( Fig. 6D View FIGURE 6 ) similar to that of male, except both rami with plumose setae on both margins, setae more than sparse in male; outer ramus 1.48 times longer than inner ramus.

Molecular data. CO1 gene sequences (GenBank accession numbers MW291608 View Materials - MW291613 View Materials ) were obtained from 6 specimens of the new species. Additionally, one sequences were determined from G. zeongogensis specimen, and four sequences from four species retrieved from National Center for Biotechnology Information (NCBI). Intraspecific variation of the CO1 gene fragment of the new species ranged from 0.2% to 0.8%, while interspecific variation ranged from 29.1% ( G. baengnyeongensis sp. nov. and G. gageoensis ) to 40.8% ( G. baengnyeongensis sp. nov. and G. koreanus ) ( Figure 8 View FIGURE 8 , Table 1 View TABLE 1 ).

Remarks. Up to now, G. baengnyeongensis sp. nov. and G. zeongogensis Lee and Kim, 1980 have been regarded as the same species, because both species commonly bear calceoli on antenna 2. However, prominent evidence found in this study, showed that these are two different species. Gammarus baengnyeongensis has a broader palm and more gradual angle in gnathopod 2, and setose telson. Also, length ratio of the outer ramus to inner ramus of uropod 3 in G. baengnyeongensis is comparatively longer than that of G. zeongogoensis . Length ratio was 1.00: 0.71 ± 0.01 (n = 25) in G. baengnyeongensis , and 1.00: 0.55 ± 0.01 (n = 25) in G. zeongogensis ( Fig. 7 View FIGURE 7 ). The difference shown in uropod 3, length ratio of outer ramus to inner ramus, between the two species was statistically significant (P <0.05, Fig. 7 View FIGURE 7 ). Gammarus baengnyeongensis sp. nov. is similar to G. koreanus Uéno, 1940 in having a few tufts of short setae and calceoli on antenna 2. Karaman (1984) elevated G. (Rivulogammarus) pulex koreanus to species level, G. koreanus which reported in North Korea, with description only. Since then, he illustrated for G. koreanus and compared to similar species G. suifunensis Martynov, 1925 ( Karaman, 1991) . As a result of referring to previous studies, the new species is distinguished from suitable straight setae on carpi-propodi in gnathopods 1-2 and posterior margins of pereopods 3-4. As Pinkster (1983) and Goedmakers (1972) stated, differences in the shape of gnathopod 2 and length ratio of the outer and inner ramus of uropod 3 are “stable characteristics.” Previous molecular study also corresponded with this result, demonstrating that freshwater Gammarus in South Korea could be distinguished into 39 different species in total, based on mtDNA CO1 sequence ( Kim, 2008). In consequence, it is difficult to consider these as a mere intra-specific variation.

G. baengnyeongensis is also similar to G. fossarum Koch, 1835 , G. qinling Hou and Li, 2018 , and G. zhigangi Hou and Li, 2018 . In males, antenna 2 bear calceoli, and gnathopods 1 and 2 bear medial palmar spines. However, in G. baengnyeongensis , the basis of pereopod 7 is broader than those of G. fossarum , G. qinling , and G. zhigangi . Also, in G. baengnyeongensis , the outer ramus of uropod 3 has plumose setae (simple setae in G. fossarum ) on the outer margin, and ratio of the outer ramus to inner ramus in G. baengnyeongensis is comparatively longer than those of congeners. The differences stated above were stable and constant. We present morphologically different characteristics in Table 2 View TABLE 2 .