Caprella carinata Arimoto, 1934

Kim, So-Yeon Shin and Young-Hyo, 2025, A new record of the species Caprella carinata (Crustacea, Amphipoda, Caprellidae) from Korean waters, Journal of Species Research 14 (2), pp. 200-205 : 201-204

Caprella carinata Arimoto, 1934

나AEḦnjņaeffių대ȒNj (ljḏ)* ( Figs. 2 - 4 )

Caprella carinata Arimoto, 1934: 496 , figs. 2, 8, 17, 21 - 22, 27.

Caprella (Caprella) carinata : Arimoto, 1976: 97, figs. 51 - 53.

Caprella eximia sensu Lee & Hong, 2011: 59 , fig. 42D, E.

Material examined. 35 males, 41 females, Geojin-ri , Geojin-eup , Goseong-gun, Gangwon-do, Korea, 38°27 ʹ 09 ʺ N, 128°28 ʹ 24 ʺ E, S.G. Lee, by SCUBA diving, 29 August 2018 ; 12 males, 6 females, Namae-ri , Hyeonnam-myeon , Yangyang-gun, Gangwon-do, Korea, 37°56 ʹ 39 ʺ N, 128° 47 ʹ 43 ʺ E, S.G. Lee, by SCUBA diving, 30 August 2018 ; 8 males, 9 females, Gyo-dong , Samcheok-si, Gangwon-do, Korea, 37°28 ʹ 01 ʺ N, 129°10 ʹ 55 ʺ E, S.G. Lee, by SCUBA diving, 31 August 2018 ; 2 males, 3 females, Gajin-ri , Jukwang-myeon , Goseong-gun, Gangwon-do, Korea, 38°22 ʹ 44 ʺ N, 128°31 ʹ 32 ʺ E, S.G. Lee, by SCUBA diving, 21 April 2019 ; 2 males, Chodo-port , Hyeonnae-myeon , Goseong-gun, Gangwon-do, Korea, 38°29 ʹ 08 ʺ N, 128°26 ʹ 19 ʺ E, Y.H. Kim, by port survey, 11 January 2023 .

Description. Male (MABIK CR00257943): Body ( Figs. 2A , 3A ) 11.6 mm long. Head smooth without process. Eyes small and round. Pereonite 1 elongate and fused with head; pereonite 2 with a projection anterodorsally, a pair of projections laterally, two pairs of projections posterodorsally and two pairs of anteriorly curved projections middorsally and posterodorsally; pereonite 3 longest; pereonites 3, 4 with dorsal and lateral projections, elongated gill; pereonite 5 subequal to pereonites 2, 4, with dorsal and lateral projections; pereonites 6, 7 short, with dorsal projections; length ratio of pereonites 2 - 7 = 1.00: 1.06: 0.99: 1.00: 0.50: 0.40.

Antenna 1 ( Fig. 3B ) 0.67 × body length; peduncular articles with sparse short; length ratio of peduncular articles 1 - 3 = 1.00: 1.58: 1.17; flagellum slender, 21-ar- ticulate, 0.84 × peduncle, each article with 1 aesthetasc ventrodistally.

Antenna 2 ( Fig. 3C ) setose, shorter than antenna 1, not reaching the distal end of peduncular article 3 of antenna 1; peduncular articles 4, 5 and flagellum article 1 with many long swimming setae ventrally; length ratio of peduncular articles 3 - 5 = 1.00: 3.72: 4.02; flagellum biarticulate, 0.85 × peduncular article 5.

Gnathopod 1 ( Fig. 3D ) small; basis broken, with an- terodistal process; merus with simple setae distally; car- pus subtriangular, with expending rounded lobe and long simple setae ventrodistally; propodus narrowing distally, palm slightly convex, with unequal setae, proximal projection conspicuously provided; dactylus falcate, slightly exceeding palm; length ratio of 6 articles = 1.00: 0.31: 0.37: 0.70: 1.45: 1.33.

Gnathopod 2 ( Fig. 3E ) attached midanterior margin of pereonite 2, long and slender; basis, anterior margin ser- rate slightly; basis, ischium, merus with process on each distal portion, propodus elongate, longer than basis, width 0.38 × length, with a small robust (grasping) seta on proximal projection, palm with triangular projection near distal margin, small poison tooth situated nearly triangular

B

projection; dactylus falcate, slightly curved; length ratio of 6 articles = 1.00: 0.13: 0.24: 0.09: 1.33: 0.98.

Pereopod 5 ( Fig. 4A ), stout; basis with large triangular process posterodistally; ischium short; merus expanded posteriorly with simple setae; propodus longest, with long simple setae posteriorly, palm defined by a pair of robust (grasping) setae midanteriorly; dactylus falcate; length ratio of 6 articles = 1.00: 0.32: 1.05: 1.08: 2.16: 2.11.

Pereopod 6 ( Fig. 4B ) similar to pereopod 5, but merus more elongated than that of pereopod 5; length ratio of 6 articles = 1.00: 0.25: 1.14: 1.08: 2.16: 2.11.

Pereopod 7 ( Fig. 4C ) similar to pereopod 6, but basis and merus narrower and more elongated than that of pereopod 6; length ratio of 6 articles = 1.00: 0.18: 0.91: 0.77: 1.50: 1.16.

Abdomen ( Fig. 4D ) with a pair of appendages, lateral lobes and a dorsal lobe; plumose setae on dorsal lobe missing; penes medial.

Female (DKUAMP202410): Body ( Figs. 2B , 4E ) about 7.9 mm long; generally as in male, but stouter than male, pereonites 3, 4 with rounded brood pouches.

Gnathopod 2 ( Fig. 4F ) similar to that of male but each article shorter than those of male.

Abdomen ( Fig. 4G ) without appendage, with a pair of lateral lobes and a dorsal lobe; with a pair of plumose setae on dorsal lobe.

Remarks. Caprella carinata is morphologically similar to C. acanthogaster Mayer, 1890 , C. eximia Mayer, 1890 , and C. mutica Schurin, 1935 , and can be characterized by the following features: (1) pereonites 2 - 5 with dorsal projections; (2) gnathopod 2 elongate, with propodus bear- ing a poison tooth and a robust (grasping) seta; (3) gill elongated; and (4) pereopods 5 - 7, bases with triangular process posterodistally and palms of propodi defined by a pair of midanterior robust (grasping) setae ( Mayer, 1890; Arimoto, 1976; Lee and Hong, 2011; Heo et al., 2020). These morphological similarities often lead to misidentification among these species. However, C. carinata can be distinguished from these species by the following features: (1) pereonite 1 with anteriorly curved dorsal projection (vs. without dorsal projection on C. acanthogaster , C. eximia , and C. mutica ); (2) pereonite 2 and gnathopod 2 without hair (vs. with hair on C. mutica ); (3) pereonites 2 - 5 with lateral projections (vs. without lateral projection in C. eximia ); (4) antenna 1, peduncular articles of equal thickness (vs. peduncular article 3 widening distally in C. acanthogaster and C. mutica ); and (5) gnathopod 2, propodus with straight poison tooth (vs. curved poison tooth in C. eximia ) (see Table 1).

Confusion between Caprella acanthogaster and C. mutica is common ( Arimoto, 1976; Kim and Lee, 1978; Heo et al., 2020), and historical records have also mis- identified C. carinata as C. eximia ( Lee and Hong, 2011) . Distinguishing these species is particularly challenging in juvenile or female specimens, underscoring the need for refined classification keys and molecular data to clarify the taxonomy of these closely related species.

Distribution. Korea (East Sea), Japan (Yamada Bay, Kuji Bay, Sunosaki to Kinkazan).

Figures

Fig. 2. Caprella carinata, A, adult male, 11.6mm, habitus; B, adult female, 7.9 mm, habitus. Scale bars:A, B=2.0 mm.

Fig. 3. Caprella carinata, adult male, 11.6 mm. A, habitus; B, antenna 1; C, antenna 2; D, gnathopod 1; E, gnathopod 2. Scale bars: A= 2 mm, B=1 mm, C, E=0.4 mm, D=0.2 mm.

Fig. 4. Caprella carinata, adult male, 11.6 mm. A, pereopod 5; B, pereopod 6; C, pereopod 7; D, abdomen.Adult female, 7.9 mm. E, habitus; F, gnathopod 2; G, abdomen. Scale bars: E=1 mm,A-C, F=0.4 mm, D, G=0.1 mm.