Ceradocus Costa, 1853

Sir, Sally & White, Kristine N., 2022, Maerid amphipods (Crustacea: Amphipoda) from Okinawa, Japan with description of a new species, Zootaxa 5093 (5), pp. 569-583 : 570-574

Genus Ceradocus Costa, 1853

( Figs 1A, B , 2–3 )

Ceradocus mizani Lim, Azman & Othman, 2010

Ceradocus mizani Lim, Azman & Othman, 2010: 24–31 , figs 1–5. Material examined. 13 specimens, 17 November 2011, Kaichu Doro Site 2S; 2 specimens, 17 November 2011, Kaichu Doro Site 4N; 1 specimen, 17 November 2011, Kaichu Doro Site 4S; 9 specimens, 2 February 2012, Kaichu Doro Site 2S; 2 specimens, 2 February 2012, Kaichu Doro Site 4N, NMST-Cr 29016, Male, 8.7 mm, Female, 8.7 mm; 14 specimens, 2 February 2012, Kaichu Doro Site 4S; 12 specimens, 27 April 2012, Kaichu Doro Site 2S; 3 specimens, 27 April 2012, Kaichu Doro Site 3S; 22 specimens, 27 April 2012, Kaichu Doro Site 4S; 4 specimens, 19 July 2012, Kaichu Doro Site 2S.

Diagnosis. Gnathopod 2 of male asymmetrical; larger male gnathopod 2 propodus palm with two large trapezoidal projections distally; smaller male gnathopod 2 propodus palm without large projections. Pereopods 5–7 bases with acute posterodistal lobe. Pleonites and urosomites 1–3 with many dorsal serrations, epimera 1–3 with posterior, posteroventral, and ventral teeth. Uropod 3 enlarged, both rami wide.

Description of male (8.7 mm). Head ( Fig. 1A ): eyes ovate; lateral cephalic lobe rounded, anteroventral margin with notch, anteroventral corner rounded. Antenna 1: length 1.8 × length of antenna 2; peduncular articles 1–3 length ratio 1.0: 0.9: 0.2; article 2 ventral margin lined with short setae; accessory flagellum 4-articulate; flagellum 26-articulate. Antenna 2: peduncular article 2 gland cone reaching to end of article 3, flagellum 12-articulate.

Pereon. Gnathopod 1 ( Fig. 2A ): subchelate; coxa anterior margin produced, anteroventral corner acute, basis anterior margin with few short setae, posterior margin with few long and short setae; merus subcylindrical with short and long setae; carpus as long as propodus, medial surface with 5 rows of simple setae and 5 rows of plumose setae, propodus palm oblique, serrate, densely setose; dactylus falcate. Gnathopod 2 ( Fig. 2C, D ): assymetrical, coxa subquadrate; larger gnathopod 2 basis slender, anterior margin with 1 long and several short setae, posterior margin with 3 short and 3 long setae; merus with sharp posteroventral spine; carpus compressed, subtriangular; propodus subrectangular, palm oblique with two large trapezoidal projections and a medial depression, with several robust setae along margin; dactylus falcate, reaching 0.5 × length of propodus; smaller gnathopod 2 basis slender, anterior margin with 1 long and several short setae, posterior margin with several medium setae; merus with sharp posteroventral spine; carpus about 0.8 × length of propodus; propodus palm oblique, weakly sinuate, with several robust setae along margin; dactylus falcate, reaching 0.4 × length of propodus. Pereopod 3: coxa square; basis moderately slender, both margins lined with short setae; merus slightly shorter than propodus; carpus and propodus subequal in length; dactylus stout. Pereopod 4: coxa subtriangular; basis moderately slender, anterior margin lined with short setae, posterior margin with medium setae; merus slightly shorter than propodus; carpus and propodus subequal in length; dactylus stout. Pereopods 5–6 missing. Pereopod 7: basis weakly expanded, posterior margin straight, serrate, posteroventral corner with acute process; merus slightly broadened, shorter than carpus and propodus; dactylus stout.

Pleon. Pleonites 1–3 ( Fig. 2F–H ): serrated dorsally. Epimera 1–3 ( Fig. 2E ): posterior margins serrate, epimeron 3 posteroventral margin strongly produced. Urosomite 1 ( Fig. 2I ): with 11 dorsal serrations; Urosomite 2 ( Fig. 2J );: with 6 dorsal serrations. Uropod 1: peduncle slightly longer than rami, with ventrodistal spur, 1 basofacial seta, inner margin lined with robust setae, rami subequal in length, each with several robust marginal setae and apices each with 3 robust setae. Uropod 2: peduncle shorter than rami, inner margin lined with robust setae, rami subequal in length, each with several robust marginal setae and apices each with 3 robust setae. Uropod 3 missing. Telson ( Fig. 2B ): deeply cleft, each lobe with 3 subapical setae, outer margin of each lobe with 1 plumose seta.

Description of female (8.7 mm). Similar in all aspects to male except for the following. Gnathopod 1 ( Fig. 3E ): smaller than in male. Gnathopod 2 ( Fig. 3F ): symmetrical, coxa subrectangular; basis slender, anterior margin with few short setae, posterior margin with few long setae; merus with sharp posteroventral spine; carpus about 0.5 × length of propodus; propodus palm oblique, serrate, with several robust setae along margin; dactylus falcate, reaching 0.5 × length of propodus. Pereopod 5 ( Fig. 3A ): coxa with anteroventral lobe; basis weakly expanded, posterior margin straight, serrate, posteroventral corner with acute process; merus slightly broadened, shorter than carpus and propodus; dactylus stout. Pereopod 6 ( Fig. 3B ): coxa with small anteroventral lobe and 2 medium setae; basis weakly expanded, posterior margin straight, serrate, posteroventral corner with acute process; merus slightly broadened, shorter than carpus and propodus; dactylus stout. Pereopod 7 ( Fig. 3C ): coxa with 2 anteroventral setae; basis weakly expanded, posterior margin straight, serrate, posteroventral corner with acute process; merus slightly broadened, shorter than carpus and propodus; dactylus missing. Uropod 3 ( Fig. 3D ): peduncle less than half length of rami, with several robust setae; rami subequal, foliaceous, margins lined with robust setae, apices each with 4 robust setae.

Remarks. The specimens examined from Okinawa agree closely with the original description of Ceradocus mizani with two discrepancies. Lim et al. (2010) describe the posterior margins of pereopods 5–7 bases as casteloserrate, but the illustration is clearly crenulate, as seen in the Okinawan specimens.The trapezoidal projections on the propodus palm of the larger male gnathopod 2 in the Okinawan specimens match the illustration provided by Lim et al. (2010), although the original description simply states that the palm is sculptured. Pending examination of type material and more material from Okinawa, the authors feel confident that this species is correctly identified as C. mizani . Collection of C. mizani from Okinawa Island increases the number of Japanese Ceradocus species to five. Ceradocus mizani differs from the other Japanese species in the following: C. capensis has a more transverse male gnathopod 2 palm with a rounded projection and few serrations on epimera 1–3 posterior margins; C. inermis has a more transverse male gnathopod 2 palm with pointed projection and few serrations on epimera 1–3 posterior margins; C. kiiensis has a shallow excavation on male gnathopod 2 propodus palm; and C. laevis has a triangular projection on male gnathopod 2 propodus palm. In addition, C. mizani is similar to rubromaculatus sensu Ren, 1998 , but C. rubromaculatus differs in having a longer antenna 1 peduncle, a less pronounced projection on the male gnathopod 2 propodus palm, few serrations on epimera 1–3 posterior margins, and more robust setae on the telson.

Distribution. Japan: Okinawa, (present study); Malaysia, Terengganu: Pulau Perhentiaan Besar, South China Sea ( Lim et al. 2010).

Figures

FIGURE 1. Photographs of examined specimens. A, Ceradocus mizani, male, 8.7 mm, (uropod 3 missing), 2 February 2012, Kaichu Doro Site 4N, NMST-Cr 29016; B, C. mizani, female, 8.7 mm, 2 February 2012, Kaichu Doro Site 4N, NMST-Cr 29016. C,Elasmopus mukuinu sp. nov., holotype, male, 6.1 mm, 27 April 2012, Kaichu Doro Site 2N, NMST-Cr 29017;; D, E. mukuinu sp. nov., paratype, female, 4.2 mm, same station data, NMST-Cr 29019. Scale bars: 1 mm.

FIGURE 2. Ceradocus mizani Lim, Azman & Othman, 2010 male, 8.7 mm. A, gnathopod 1, medial; B, telson; C, small gnathopod 2, medial; D, large gnathopod 2, medial; E, epimera 1–3; F, pleonite 1, dorsal; G, pleonite 2. Dorsal; H, pleonite 3, dorsal; I, urosomite 1, dorsal; J, urosomite 2, dorsal. Scale bars: 0.5 mm.

FIGURE 3. Ceradocus mizani Lim, Azman & Othman, 2010 female, 8.7 mm.A, pereopod 5; B, pereopod 6; C, pereopod 7; D, uropod 3; E, gnathopod 1, medial; F, gnathopod 2, medial. Scale bars: 0.5 mm.