Paradexamine rotundogena, Zhang & Kim & Kim, 2022

Zhang, Xin, Kim, Kyung-Won & Kim, Young-Hyo, 2022, Two new species of the genus Paradexamine (Crustacea, Amphipoda, Dexaminidae) from Korean Waters, ZooKeys 1117, pp. 37-52 : 37

Paradexamine rotundogena sp. nov.

Figs 2B , 6 , 7 Korean name: Dung-geun-ppyam-yeop-ga-si-but-eun-kko-ri-yeop-sae-u, new

Type material.

Holotype: female, 5.0 mm, MABIK CR00250814, Korea, Gyeongsangnam-do, Geomundo Island, Guroba, 34°00'52"N, 127°17'41"E, 09 July 2019, scuba collection, depth 10-15 m, S.G. Lee & Y.H. Kim leg. Paratypes: two females, 3.4 mm and 4.5 mm, DKUAMP202203, same station data as holotype.

Additional material examined.

1 female, Korea, Gyeongsangnam-do, Geomundo Island , 34°00'43"N, 127°18'05"E, 06 June 2018, S.H. Kim leg. 4 females, Korea, Chujado Island , 33°56'43"N, 126°18'42"E, Z. Xin, K.W. Kim, & Y.H. Kim leg., 28 August 2021 .

Diagnosis.

Lateral cephalic lobe rounded. Eye medium-sized. Dorsal pleonites tooth formulae 3-3-3-3, rear to front. Antenna 1, peduncular article 2 slightly longer than article 1. Maxilla 1, inner plate without apical seta. Maxilliped, inner plate without lateral setae. Gnathopod 1, propodus broad, palm steeply angled. Pereopods 3-7 spinose. Pereopod 7, basis subquadrate, with irregular serrations posteriorly. Telson deeply cleft nearly to the base.

Description.

Holotype, female, MABIK CR00250814. Body (Fig. 6A ) length about 5.0 mm. Cephalic lobe rounded. Eye medium-sized, subround. Pereonites smooth.

Pleonites 1-3 (Figs 6B ), dorsal tooth formulae 3-3-3-3, rear to front; pleonal epimera 1-3 each with posteroventral tooth, its gradually getting bigger distally and posterior margins with irregularly crenulated; urosomite 1 with one dorsodistal carinate tooth and a pair of dorsolateral teeth with a spine.

Antenna 1 (Fig. 6C ) slightly longer than half as long as body length; peduncular articles rectangular, length ratio of peduncular articles 1-3 = 1.00: 1.19: 0.41; accessory flagellum small, with three apical setules; flagellum about 1.3 times as long as peduncle, 15-articulate.

Antenna 2 (Fig. 6D ) one-third of the body length and two-thirds of antenna 1 length. peduncular articles 1-3 short, peduncular articles 4 and 5 elongated, length ratio of peduncular articles 3-5 = 1.00: 4.14: 4.42; flagellum 7-articulate, 1.4 times as long as peduncular article 5.

Lower lip (Fig. 6E ) inner lobe elongate-ovate, covered with patch of pubescence; outer lobe with three or four cusps; mandibular process produced subacutely.

Left mandible (Fig. 6F ) incisor produced forward, with eight blunt teeth; lacinia mobilis bifid, upper part with six teeth, lower part with two blunt teeth; three accessory spines placed between lacinia mobilis and molar process; molar process developed, truncate.

Right mandible (Fig. 6G ) similar to left mandible, except two accessory spines placed between lacinia mobilis and molar process.

Maxilla 1 (Fig. 6H ) inner plate small, elongate, without apical seta; outer plate with 11 tooth-like spines (simple, bifid, and denticulate) apically; palp slender, not reaching end of outer plate, with a long apical seta.

Maxilla 2 (Fig. 6I ) inner plate much shorter than outer one, with four apical setae; outer plate with four subapical and three apical setae.

Maxilliped (Fig. 6J ) inner plate small, with one apical setae and without lateral setae; outer plate large, elongate-ovate, slightly extending beyond end of palp article 3, inner margin with 15 conical teeth and five simple setae apically; palp 4 articulate, rather slender, inner margin setaceous, slightly extending outer plate.

Gnathopod 1, coxa (Fig. 7A ) trapezoidal, anterior margin rounded, with 13 unequal simple setae, posterior margin straight, unarmed; carpus (Fig. 7B ) subtriangular, subequal to propodus, with six ventral setae; propodus broad, gradually widening distally, without oblique row of setae medially, palm steeply angled, with a row of short setae, delimited by a group of four spines; dactylus falcate, fitting palm.

Gnathopod 2 (Fig. 7C ) similar to gnathopod 1, but coxa narrowly rectangular and carpus elongate, 1.36 times as long as propodus.

Pereopod 3 (Fig. 7D ) slender, spinose; coxa tapering distally; length ratio of articles 2-7 = 1.00: 0.27: 0.70: 0.53: 0.87: 0.40.

Pereopod 4 (Fig. 7E ) similar to pereopod 3, except coxa 4 wider than coxa 3 ventrally; length ratio of articles 2-7 = 1.00: 0.25: 0.69: 0.53: 0.78: 0.38.

Pereopod 5 (Fig. 7F ), coxa quadrate, bilobate, anterior rounded lobe protruding downward; basis longish ovate form, posteroventral lobe roundly downward, reaching somewhat distal margin of ischium, with several clusters of long to short spines along anterior margin, posterior margin straight, unarmed; ischium to dactylus slender, setose; length ratio of articles 2-7 = 1.00: 0.18: 0.70: 0.58: 0.50: 0.34.

Pereopod 6 (Fig. 7G ) coxa 6 bilobate, similar to coxa 5, but shallower than coxa 5; basis ovate, posterior margin rounded, weakly serrate, slightly excavate posterodistally; length ratio of articles 2-7 = 1.00: 0.15: 0.85: 1.08: 0.77: 0.30.

Pereopod 7 (Fig. 7H ) coxa small, semicircular; basis subquadrate, width 0.91 times length, produced posteriorly, anterior margin straight, posterior margin with irregular serrations; length ratio of articles 2-7 = 1.00: 0.26: 0.60: 1.29: 0.72: 0.29.

Uropod 1 (Fig. 7I ) peduncle subrectangular, with five dorsolateral, three medial, and one apicolateral large spines; inner ramus slightly shorter than peduncle, with two longitudinal rows of 10 and three apical spines; outer ramus broken.

Uropod 2 (Fig. 7J ) about half length of uropod 1, with four dorsolateral and one apicomedial spines; outer ramus 0.75 times as long as peduncle, with two rows of four and three apical spines; inner ramus broken.

Uropod 3 unknown.

Telson (Fig. 7K ) longish, 2.00 times as long as wide, thoroughly cleft, lateral margin with two spines, apical margin truncate with acute cusp, serrulation, and one spine.

Etymology.

The species name is derived from the Latin rotundus (= round) and gena (= cheek), referring to the rounded cephalic lobe.

Remarks.

The new species Paradexamine rotundogena sp. nov. resembles P. tafunsaka Myers, 1995 distributed in Kosrae, Micronesia, P. levitelson Myers & LeCroy, 2009 from Queensland, Australia, and P. bisetigera Hirayama, 1984 from Tomioka Bay, Japan, in having a rounded ocular lobe and dorsal pleonite tooth formulae of 3-3-3-3, rear to front (Table 2 ). However, the new species is distinguished from its congeners in the following characteristics (compared with the characteristics of congeners in parentheses): 1) gnathopod 2 with carpus longer than propodus (vs subequal in length in P. bisetigera , shorter than in P. tafunsaka and P. levitelson ); 2) pereopod 7 with basis broad, with irregular serrations posteriorly (vs regular serrations posteriorly in P. bisetigera , P. levitelson , and P. tafunsaka ); 3) maxilla 1 with palp having one apical seta (vs two apical setae in P. tafunsaka and P. bisetigera , six apical setae in P. levitelson ); 4) maxilla 2 with inner plate without medial seta (vs with three setae in P. bisetigera ); 5) telson with two lateral spines (vs five or six lateral spines in P. bisetigera , three or four lateral spines in P. tafunsaka ).

Distribution.

South Korea (Chujado Island, Geomundo Island).

Figures

Figure 2. A Paradexamine acuta sp. nov., adult female, habitus B Paradexamine rotundogena sp. nov., adult female, habitus. Scale bar: 1.0 mm (A, B).

Figure 6. Paradexamine rotundogena sp. nov., holotype, adult female, MABIK CR 00250814, 5.5 mm A habitus B pleonal epimera 1 - 3 C antenna 1 D antenna 2 E lower lip F left mandible G right mandible H maxilla 1 I maxilla 2 J maxilliped. Scale bars: 0.5 mm (A); 0.2 mm (B-D); 0.1 mm (E-J).

Figure 7. Paradexamine rotundogena sp. nov., holotype, adult female, MABIK CR 00250814, 5.5 mm A coxa 1 B gnathopod 1 C gnathopod 2 D pereopod 3 E pereopod 4 F pereopod 5 G pereopod 6 H pereopod 7 I uropod 1 J uropod 2 K telson. Scale bars: 0.1 mm (A-C); 0.2 mm (D-K).