Caprella arimotoi Takeuchi, 1993

Heo, Jun-Haeng & Kim, Jaehong Choi and Young-Hyo, 2020, A new record of the species Caprella arimotoi (Crustacea: Amphipoda: Caprellidae) from Korean waters, Journal of Species Research 9 (4), pp. 443-447 : 444-447

Caprella arimotoi Takeuchi, 1993 ( Figs. 2-4 )

나AEẠǧffiq대ḇNj (ṵḓ)

Caprella (Spinicephala) verrucosa Arimoto, 1976: 122 , fig. 67-D.

Caprella (Spincephala [sic.]) pseudoverrucosa Arimoto, 1978: 14, fig. 7C.

Caprella arimotoi Takeuchi, 1993: 115 , figs. 1-3.

Caprella verrucosa : Lee and Hong, 2011: 32, fig. 18 [not Caprella verrucosa Boeck, 1871 ].

Material examined. 1♂ (NIBRIV0000876687), 1$ (NIBRIV0000876686), Kuldo Island , Baegil-ri , Gwayeokmyeon, Goheung-gun, Jeollanam-do, Korea, 34°40′50.43″ N, 127°28′16.64″E, 24 Aug 2008, collected by S.S. Hong ; 1♂ (MARBK-201), Changjwa-ri , Hansan-myeon, Tongyeong-si, Gyeongsangnam-do, 34°46′54.46″N, 128° 29′39.13″E, 30 Sep 2019, collected by S.Y. Shin, Y.H. Kim.

Description. Male, body ( Figs. 2A , 3A ) long and slender, 6.95 mm long (NIBRIV0000876687). Head round, with triangular forwardly pointing projection anterodorsally. Eye small and round. Pereonites 2-4 with mid-dorsal and posterodorsal blunt projections; pereonites 3-4 with elongated elliptical gills; gill elongated, length 3.00 × width; pereonite 5 with mid-dorsal blunt projection; pereonites 6-7 short, without dorsal projection; length ratio of pereonites 2-7 = 1.00: 1.07: 0.89: 0.79: 0.36: 0.32.

Antenna 1 ( Fig. 3B ) 0.33 × body length, peduncular articles moderately, with sparse short setae, peduncular article 3 slightly widening distally; length ratio of peduncular articles 1-3 = 1.00: 1.42: 0.64; flagellum 11-articulate, subequal in length to combined peduncular articles 1-3.

Antenna 2 ( Fig. 3C ) setose, 0.76 × antenna 1; peduncular articles 4-5 and flagellum article 1 with swimming setae on posterior margin; length ratio of peduncular articles 3-5 = 1.00: 2.67: 2.75; flagellum article biarticulate, subequal in length to peduncular article 5, proximal article 3.71× distal one.

Gnathopod 1 ( Fig. 3D ) small, basis expanded posteriorly; ischium shorter than merus with simple setae posteriorly; merus subquadrate, with unequal simple setae; carpus expanded posteriorly; propodus subtriangular, narrowing distally, 1.40 × basis, palm weakly serrated, with unequal simple setae, defined by a pair of grasping spines; dactylus falcate, inner margin irregularly serrate, length ratio of 6 articles =1.00: 0.27: 0.5: 0.33: 1.40: 1.33.

Gnathopod 2 ( Fig. 3E ) attached to rather anteroventral portion of pereonite 2; basis elongate, 0.39 × pereonite 2; carpus very short, unarmed; propodus subovate, width 0.35 × length, palm somewhat concave medially, with triangular projection and unequal simple setae near subdistal

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A C D B E

margin, sharp projection located subproximal margin, below the subproximal projection with 1 small spine and unequal setae; dactylus falcate, inner margin serrulate; length ratio of 6 articles = 1.00: 0.15: 0.30: 0.13: 1.70: 0.98.

Pereopod 5 ( Fig. 3F ), basis with process posterodistally; ischium short; merus expanded posteriorly, with 2 clusters of setae; propodus subrectangular, longest, both margins with unequal simple setae, palm defined by a pair of grasping spines anteroproximally; dactylus falcate; length ratio of 6 articles = 1.00: 0.42: 1.07: 0.93: 2.07: 1.50.

Pereopod 6 ( Fig. 3G ) similar to pereopod 5, but more elongated than pereopod 5; length ratio of 6 articles = 1.00: 0.40: 1.07: 1.00: 2.30: 1.13.

Pereopod 7 ( Fig. 3H ) similar to pereopod 5, but more elongated than pereopods 5 and 6; length ratio of 6 articles= 1.00: 0.24: 1.00: 0.84: 1.80: 1.00.

Female, body ( Figs. 2B , 4A) slender, 5.10 mm long (NIBRIV0000876686). Pereonites 3-4 with oostegites; length ratio of pereonites 2-7 = 1.00: 0.82: 0.86: 0.46: 0.39.

Antenna 1 ( Fig. 4B) similar to that of male; length ratio of peduncular articles 1-3 = 1.00: 1.37: 0.74; flagellum 9-articulate.

Antenna 2 ( Fig. 4C) similar to that of male; length ratio of peduncular articles 3-5 = 1.00: 2.92: 2.92; flagellum biarticulate, subequal in length to peduncular article 5, proximal article 3.00× distal one.

Gnathopod 1 ( Fig. 4D) similar to but smaller than that of male.

Gnathopod 2 ( Fig. 4E), propodus subovate, slightly longer than basis; palm setose, smooth and slightly convex, without projections, defined by a pair of grasping spines posteroproximally; length ratio of 6 articles = 1.00: 0.16: 0.18: 0.06: 1.06: 0.86.

Distribution. Japan (Mukaishima Island, Seto Inland Sea, Tsushima Islands, Tateyama and Amatsu-Kominato, Chiba), Korea (South Sea).

Remarks. Takeuchi (1993) mentioned that C. arimotoi is very close to C. verrucosa with the following characteristics: 1) pereonites with dorsal blunt projections; 2) gnathopod 2, basis short; 3) propodus subovate; and 4) pereopods 5-7 with grasping spines anteroproximally. Takeuchi also mentioned that C. arimotoi can be distinguished from C. verrucosa (different characters of C. verrucosa in brackets) by a combination of the following features: (1) antenna 1, subequal to half of the body length (vs. about one third of the body length); (2) antenna 1, peduncular articles slender, each length about 4 × width (vs. 2 to 3 × width); (3) antenna 2, peduncular articles 2-3 with 4 to 5 pairs of plumose setae (vs. more than eight pairs of longer plumose setae); (4) head, mid-dorsal projection curved forward (vs. straight forward); (5) pereonites 3-4, without ventrolateral projections (vs. with ventrolateral projections); and (6) gills length 3 × width (vs. 1.5 × width) ( Takeuchi, 1993). However, these differences between these two closely related species are inapplicable to Korean specimens because some of these differences are overlap between Korean C. arimotoi and C. verrucosa specimens. Thus, we clearly show the differences between C. arimotoi and C. verrucosa as follow (different characters of C. verrucosa in parentheses): (1) pereonites 2-7 without ventrolateral projections (vs. pereonites 3-4 with ventrolateral projections); (2) pereonites 3-5 and pereopod 7 slender and elongate (vs. stout and moderate); and (3) head with triangular forwardly pointing projection mid-dorsally (vs. straight forward). Our specimens share various morphological characteristics with those of the original description by Takeuchi (1993).

Figures

Fig. 2. Caprella arimotoi Takeuchi, 1993, A, male, 6.95mm, habitus, B, female, 5.10mm, habitus. Scale bars:A, B=1.0 mm.

Fig. 3. Caprella arimotoi Takeuchi, 1993, male, 6.95 mm. A, Habitus; B, Antenna 1; C, Antenna 2; D, Gnathopod 1; E, Gnathopod 2; F, Pereopod 5; G, Pereopod 6; H, Pereopod 7. Scale bars: A=1.0 mm, B-H=0.2 mm.