Caprella iniquilibra Mayer, 1903

Kim, Kyung-Won, Choi, Jae-Hong, Shin, So-Yeon & Kim, June Kim and Young-Hyo, 2024, Amphipod (Crustacea: Malacostraca) fauna of the continental shelf region in the Southern Sea of Korea, Journal of Species Research 13 (2), pp. 159-177 : 166-168

10. Caprella iniquilibra Mayer, 1903

나PṻầṻṄḋq1fiNj (ṳạ)* ( Figs. 7 - 9 , 12B, C )

Caprella iniquilibra Mayer, 1903: 105 , pl. 4, Figs. 17 - 19.

Caprella (Caprella) iniquilibra Arimoto, 1976: 82 , Figs. 41, 42.

Material examined. 9♂♂, 17♀♀, Site 8, 17 August 2022.

Description. Male (MABIK CR00254535): Body ( Figs. 7A , 12B ) slender and smooth, 5.4 mm long. Head ( Fig. 7A ) smooth without process; eye small and round; pereonite 1 fused with head, suture present; pereonites 2 with a projection ventrally between gnathopod 2; pereonites 3, 4 with elongated gills; pereonites 5 longest; length ratio of pereonites 2 - 7 = 1.00: 0.98: 0.95: 1.32: 0.42: 0.30.

Antenna 1 ( Fig. 7B ) slender, 0.74 times body length; peduncular article 1 shortest, with several short setae; length ratio of peduncular articles 1 - 3 = 1.00: 2.12: 1.33; flagellum 13-articulate, 1.38 times peduncle, each article with 1 aesthetasc ventrodistally.

Antenna 2 ( Fig. 7C ) much shorter than antenna 1; peduncular articles 4, 5 and flagellum article 1 with swim- ming setae ventrally; length ratio of peduncular articles 3 - 5 = 1.00: 4.02: 4.48; flagellum biarticulate, 0.74 times peduncular articles 5.

Gnathopod 1 ( Fig. 7D ) small; basis expanded posteriorly; carpus subtriangular, with expending rounded lobe and long simple setae ventrally; propodus subtriangular, narrowing distally, palm slightly convex, with unequal setae, proximal projection conspicuously provided; dactylus falcate, fitting palm; length ratio of 6 articles = 1.00: 0.31: 0.45: 0.65: 1.24: 1.32.

Gnathopod 2 ( Fig. 7E ) attached to midposterior portion of pereonite 2; basis elongate, subequal to propodus, with a projection on anterodistal portion; propodus elongate, width 0.49 times length, palm with triangular projection near distal margin, poison tooth situated nearly triangular projection, with 1 robust (grasping) seta, unequal simple setae on palmar margin; length ratio of 6 articles = 1.00: 0.14: 0.17: 0.07: 1.02: 0.77.

Pereopod 5 ( Fig. 8A ) elongate and ordinary; propodus, palm with a pair of robust (grasping) setae; length ratio of 6 articles = 1.00: 0.19: 0.94: 0.71: 1.26: 1.12.

Pereopod 6 ( Fig. 8B ) similar to pereopod 5, but merus more elongated than that of pereopod 5; length ratio of 6 articles = 1.00: 0.21: 1.03: 0.74: 1.37: 1.08.

Pereopod 7 ( Fig. 8C ) similar to pereopod 6, but merus more elongated than that of pereopod 6; length ratio of 6 articles = 1.00: 0.22: 1.20: 0.73: 1.25: 0.87.

Abdomen ( Fig. 8D ) with a pair of appendages and lobes, plumose setae dorsally.

Female (DKUAMP202305): Body ( Figs. 9A , 12C ) 6.5 mm long, generally as in male, but pereonites 3, 4 with rounded brood pouches.

Gnathopod 2 ( Fig. 9B ) similar to that of male, but basis slender than that of male.

Abdomen ( Fig. 9C ) similar to that of male, but without appendages.

Distribution. Korea (south coast), Japan.

Remarks. Caprella iniquilibra is morphologically similar to C. equilibra by the following features: (1) antenna 1, length ratio of peduncular articles 1 - 3; (2) pereonite 2 with a projection midventrally between gnathopod 2; (3) gnathopod 2, propodus oval ( Mayer, 1882; Stebbing, 1888; Arimoto, 1976). However, C. iniquilibra is distinguished from C. equilibra (different characters of C. equilibra in brackets) by the following features: (1) head smooth and round, without angular projection in front(vs. with angular projection in front), (2) pereonite 5 longest (vs. pereonite 2 longest), (3) gnathopod 2, basis subequal to propodus in length (vs. shorter than propodus). Caprella iniquilibra is also similar to C. simplex but can be distinguished (different characters of C. simplex in brackets) by the following features: (1) pereonite 5 longest and smooth (vs. pereopod 2 longest, pereonite 5 with a pair of projections), (2) antenna 1 shorter than body length (vs. subequal to body length), (3) pereopods 5 - 7, propodi with robust (grasping) setae (vs. without robust (grasping) setae).

Caprella iniquilibra was first described by Mayer (1903) with a type locality in the Korea straits. However, upon checking the coordinates, it was collected in the waters of Japan, far from Korea. Subsequently, C. iniquilibra has been recorded in Japan ( Arimoto, 1976), but there is no record of it being found in Korea. Our Korean specimens are in good agreement with Mayer’s (1903) description.

Figures

Fig. 7. Caprella iniquilibra Mayer, 1903, adult male. A, habitus; B, antenna 1; C, antenna 2; D, gnathopod 1; E, gnathopod 2. Scale bars: A=1.0 mm; B, E=0.2 mm; C=0.4 mm; D=0.1 mm.

Fig. 8. Caprella iniquilibra Mayer, 1903, adult male. A, pereopod 5; B, pereopod 6; C, pereopod 7; D, abdomen. Scale bars:A-C=0.2 mm; D=0.05mm.

Fig. 9. Caprella iniquilibra Mayer, 1903, adult female. A, habitus; B, gnathopod 2; C, abdomen. Scale bars: A=1.0 mm; B=0.2 mm; C=0.05 mm.

Fig. 12. A, Caprella decipiens; B, Caprella iniquilibra, male; C, Caprella iniquilibra, female; D, Caprella verrucosa; E, Protogeton incertus; F, Pseudoproto fallax; G, Cyproidea liodactyla; H, Themisto sp.