Paradexamine acuta, 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 acuta sp. nov.

Figs 2A , 3 , 4 , 5 Korean name: Ppyo-jok-yeop-ga-si-but-eun-kko-ri-yeop-sae-u, new

Type material.

Holotype: female, 5.5 mm, MABIK CR00250813, Korea, Incheon, Baengnyeongdo Island, Dumujin, 37°58'36"N, 124°37'09"E, 13 August 2020, scuba collection in red alga Gelidium sp., depth 5-10 m, S.G. Lee & Y.H. Kim leg. Paratypes: 3 females, 4.6 mm, 5.1 mm, and 5.4 mm, DKUAMP202201, same station data as holotype.

Additional material examined.

22 females, DKUAMP202202, Korea, Incheon, Baengnyeongdo Island , 37°58'26"N, 124°38'39"E, Y.H. Kim leg., 12 August 2020 . 1 female, Korea, Chujado Island , 33°57'13"N, 126°18'08"E, Z. Xin, K.W. Kim, & Y.H. Kim leg., 27 August 2021 . 7 females, Korea, Jejudo Island, Jongdal Port , 33°29'49"N, 126°54'41"E, Y.H. Kim leg., 5 February 2022 .

Diagnosis.

Lateral cephalic lobe acute. Eye small. Dorsal pleonites tooth formulae 1-3-3-3-0, rear to front. Outer lobe of lower lip with two corns. Maxilla 1, inner plate with two setae. Maxilliped, inner plate lacking lateral setae. Antenna 1, peduncular article 2 1.25 times article 1. Gnathopod 1, propodus subovate, medial side with oblique row of 11 or 12 setae; palm oblique. Coxa 7, posterodistal corner acutely produced. Telson deeply cleft, with lateral and apical spines.

Description.

Holotype, female, MABIK CR00250813. Body (Fig. 3A ) length about 5.5 mm. Ocular lobe acutely produced. Eye small, subovate. Pereonites smooth.

Pleonites 1-3 (Fig. 3B ) dorsal tooth formulae 1-3-3-3-0, rear to front; pleonal epimera 1-3 each with posteroventral tooth, gradually enlarging distally; epimeron 1 with oblique row of 5 setae ventrally; epimeron 2 similar to pleonal epimeron 1 but with two clusters of setae anteroventrally; epimeron 3 excavate posteriorly, with five clusters of setae ventrally.

Antenna 1 (Fig. 3C ) slightly longer than half as long as body length; peduncular articles rectangular, length ratio of peduncular articles 1-3 = 1.00: 1.25: 0.25; accessory flagellum small, with three apical setules; flagellum subequal in length to peduncle, 15-articulate.

Antenna 2 (Fig. 3D ) 0.78 times as long as antenna 1; gland corn well developed; peduncular articles 3-5 setaceous facially, length ratio = 1.00: 5.00: 2.90; flagellum 1.13 times as long as peduncle, 12-articulate.

Lower lip (Fig. 3E ), inner lobe subovate, coalescent proximally, rounded apically; outer lobe with two corns, mandibular process upturned and acute.

Left mandible (Fig. 3F ), incisor produced forward, with five blunt teeth; lacinia mobilis bifid, upper part with five teeth, lower part with four teeth; three accessory spines placed between lacinia mobilis and molar process; molar process massive, developed.

Right mandible (Fig. 3G ) similar to left mandible, except two accessory spines placed between lacinia mobilis and molar process.

Maxilla 1 (Figs 3H ), inner plate with two simple setae apically; outer plate six denticulate and five bifid tooth-like spines apically; palp broad, with 11 simple setae.

Maxilla 2 (Fig. 3I ), inner plate shorter and narrower than outer plate, with nine setae; outer plate with 14 setae overall.

Maxilliped (Fig. 3J ), inner plate elongate, about one-third as long as outer plate, with three apical setae; outer plate elongate-ovate, slightly extending beyond end of palp article 3; inner margin crenulate, with 12 conical teeth which gradually increase in size toward distal end; distal half of outer margin with a row of 11 simple setae; palp 4 articulate, rather slender, inner margin setaceous, extending outer plate.

Gnathopod 1 (Fig. 4A ), coxa trapezoidal, ventral margin rounded, with unequal setae; basis slender, about half as long as gnathopod 1, with nine simple setae posteriorly; ischium small, subrectangular, 0.75 times as long as merus; carpus 1.17 times as long as propodus; propodus subovate, with oblique row of 11 setae medially, palm oblique, with a row of short setae, delimited by a group of four spines; dactylus falcate, fitting palm.

Gnathopod 2 (Fig. 4B ) similar to gnathopod 1, but longer and slenderer than gnathopod 1.

Pereopod 3 (Fig. 4C ), coxa subrectangular, one-third as wide as long, ventral margin setose; length ratio of articles 2-7 = 1.00: 0.18: 0.62: 0.50: 0.67: 0.35.

Pereopod 4 (Fig. 4D ) similar to pereopod 3.

Pereopod 5 (Fig. 5A ), coxa subquadrate, bilobate, anterior rounded lobe protruding downward, with short setae; basis with longish ovate form, posteroventral lobe rounded downward, reaching somewhat near distal margin of ischium, with several clusters of long to short spines along anterior margin; ischium to dactylus slender, setose; length ratio of articles 2-7 = 1.00: 0.18: 0.90: 0.68: 0.66: 0.20.

Pereopod 6 (Fig. 5B ), coxa 6 bilobate, similar to coxa 5, but shallower than coxa 5; basis ovate, posterior margin rounded and finely serrulate; length ratio of articles 2-7 = 1.00: 0.20: 1.10: 1.02: 1.15: 0.59.

Pereopod 7 (Fig. 5C ), coxa subquadrate, with acutely produced posteroventrally; basis subrectangular, narrow, width 0.57 times length; length ratio of articles 2-7 = 1.00: 0.24: 0.71: 1.07: 0.71: 0.36.

Uropod 1 (Fig. 5D ), peduncle subrectangular, subequal to outer ramus, with six dorsolateral, four medial, three basofacial, and one apicolateral large spines; inner ramus slightly longer than outer ramus.

Uropod 2 (Fig. 5E ) 0.64 times as long as uropod 1; peduncle subequal to outer ramus, with two dorsolateral and one apicomedial spines; inner ramus slightly longer than outer ramus, apical portion broken.

Uropod 3 (Fig. 5F ) longer and broader than uropod 2; peduncle 0.69 times as long as outer ramus, with three dorsolateral, five medial, and one apicolateral large spines; both rami subequal in length.

Telson (Fig. 5G ) longish, 2.37 times as long as wide, thoroughly cleft, lateral margin with a row of unequal spines, apical margin truncate, with serrulation and one spine.

Male. Unknown.

Immature female, 3.0 mm, DKUAMP202202. Gnathopod 1, propodus subovate, with oblique row of eight setae medially; pereopod 6, basis ovate, posterior margin rounded and finely serrulate; coxa 7 pointed posteroventrally; telson, lateral margin with a row of seven spines.

Etymology.

The species name is derived from the Latin acutus (= sharp, pointed), referring to the acute cephalic lobe and posteroventral acute projection on coxa 7.

Remarks.

The new species Paradexamine acuta sp. nov. resembles P. houtete J.L. Barnard, 1972b from New Zealand, P. jindoensis Kim & Lee, 2008 from Jindo Island, Korea, P. gigas Hirayama, 1984, P. marlie s.l., and P. micronesica Ledoyer, 1978 from Tomioka Bay, Japan, in having acute ocular lobe and dorsal pleonites tooth formulae 1-3-3-3-0, rear to front (Table 1 ). However, this new species is distinguished from its congeners in the following characteristics (compared with the characteristics of congeners in parentheses): 1) inner plate of maxilla 1 with five lateral setae (vs without setae in P. gigas , P. houtete ); 2) maxilliped, inner plate without lateral setae (vs seven lateral setae in P. jindoensis ); 3) gnathopod 1 having medial setae on propodus with 10 or 11 setae (vs four or five setae in P. gigas , P. houtete , P. micronesica ); 4) pereopod 6 with basis ovate, roundly produced posteriorly and with serrulations (vs tapering posterodistally in P. gigas , P. houtete , P. micronesica ); 5) pereopod 7 with coxa pointed posteroventrally (vs rounded posteroventrally in P. gigas , P. jindoensis ); 6) pereopod 7, basis subrectangular and narrow (vs subovate in P. gigas , elongate-ovate and moderate in P. micronesica ).

In general, Paradexamine acuta sp. nov. is very similar to P. marlie s.l. from Japanese waters as described and figured by Hirayama (1984). Paradexamine marlie s.l. from Japan differs from the original description of P. marlie from Australia ( Barnard 1972a) in having the dorsal pleonites tooth formulae 1-3-3-3-0 and coxa 7 posteroventrally pointed. In many ways, including these two major characteristics, P. marlie s.l. from Japan is more similar to P. acuta sp. nov. However, as we have not had the opportunity to examine Hirayama’s (1984) type material, we cannot confidently determine if they are the same species. Nevertheless, P. marlie s.l. Hirayama could be re-established or synonymized with P. acuta sp. nov. in the future.

Distribution.

South Korea (Baengnyeongdo Island, Chujado Island, Jejudo 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 3. Paradexamine acuta sp. nov., holotype, adult female, MABIK CR 00250813, 5.0 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); 0.1 mm (C-J).

Figure 4. Paradexamine acuta sp. nov., holotype, adult female, MABIK CR 00250813, 5.0 mm A gnathopod 1 B gnathopod 2 C pereopod 3 D pereopod 4. Scale bars: 0.2 mm (A, B), 0.1 mm (C, D).

Figure 5. Paradexamine acuta sp. nov., holotype, adult female, MABIK CR 00250813, 5.0 mm A pereopod 5 B pereopod 6 C pereopod 7 D uropod 1 E uropod 2 F uropod 3 G telson. Scale bar: 0.2 mm (A-G).