Ceradocus laevis Oleröd, 1970

Ariyama, Hiroyuki, 2019, Two species of Ceradocus collected from coastal areas in Japan, with description of a new species (Crustacea: Amphipoda: Maeridae), Zootaxa 4658 (2), pp. 297-316 : 307-313

Ceradocus laevis Oleröd, 1970

[Japanese name: Togenashi-nokogiriyokoebi, new]

( Figs 7–11 )

Ceradocus laevis Oleröd, 1970: 376 , figs 55–72.— Krapp-Schickel & Vader, 2009: 2061 (key).— Dang & Le, 2011: 3.— Ren, 2012: 184, fig. 79.— White, 2015: 141.— Alves, Johnsson & Senna, 2019: 135 (key).

Material examined. Two males, 6.9 and 6.1 mm (OMNH-Ar-11275, 11276), Hinai Beach, Iriomote Island, Okinawa Prefecture, 24°24'49"N, 123°48'22"E ( Fig. 1C ), 0.5 m depth, dead coral and fine sand bottom, 14 July 2015, coll. H. Ariyama; male, 4.6 mm (OMNH-Ar-11277) and ovigerous female, 7.4 mm (OMNH-Ar-11278), Shirahama, Iriomote Island , Okinawa Prefecture, 24°21'44"N, 123°44'45"E ( Fig. 1C ), 0.05 m depth, dead coral and fine sand bottom, 16 July 2015, coll. H. Ariyama ; male, 6.9 mm (OMNH-Ar-11279) and female with juveniles, 7.0 mm (OMNH-Ar-11280), Awase, Okinawa Island , Okinawa Prefecture, 26°18'48"N, 127°50'15"E ( Fig. 1B ), intertidal, dead coral and fine sand bottom, 3 July 2015, coll. H. Ariyama.

Type locality. Puerto Garera in Mindoro , Philippines ( Oleröd 1970) .

Diagnosis. Male gnathopod 2 asymmetrical; larger male gnathopod 2 with strongly oblique palm having triangular and small trapezoidal projections distally; smaller male gnathopod 2, palm oblique, smooth, defined by tiny projection. Pereopods 5–7, bases with rounded posterodistal lobe. Pleonites 1–3 and urosomites 1–3 without dorsal teeth; pleonal epimera 1–2 each bearing 1 posteroventral and 1 ventral teeth, epimeron 3 with 1–2 posterior, 1 posteroventral and 1–2 ventral teeth. Uropod 3 enlarged, both rami wide. Telson , each lobe with 1 long and 1 short robust setae.

Description. Based on male, 6.9 mm (OMNH-Ar-11275), and male, 6.9 mm (OMNH-Ar-11279) for pleonal epimera.

Head ( Figs 7–8 ). Eyes relatively large, about quarter of head length. Antenna 1 poorly setose; peduncle with ratio of lengths of articles 1–3 1:1.15:0.2, article 1 with 4 posteromedial robust setae, anterodistal corner with bundle of setae; accessory flagellum short, with 5 articles, terminal article minute; primary flagellum long, with>16 articles. Antenna 2 relatively short, weakly setose, with ratio of lengths of peduncular articles 3–5 1:2.5:2.05; flagellum short, with 9 articles, terminal article minute. Upper lip, ventral margin rounded, with short setae. Mandible, each incisor bearing 4 cusps, left lacinia mobilis 4-dentate, with 7 accessory setae, right lacinia mobilis bifid, 5-dentate, with 7 accessory setae, each molar developed; palp articles 1 – 3 length ratio (excluding distal tooth of article 1) 1:2.3:0.8, article 2 weakly setose, article 3 with several long setae at tip. Lower lip, distal margins of inner and outer lobes setose, mandibular processes small. Maxilla 1, inner plate setose on mediodistal margin, outer plate with 9 apical robust setae, palp with many apical setae. Maxilla 2, outer plate same size as inner plate; both plates bearing many apical setae, inner plate with dorsomedial setae. Maxilliped, inner plate truncate, distally setose, distomedial corner with 3 robust setae ventrally; outer plate with 14 long-to-short robust setae on distomedial margin; palp 4- articulate, articles 2 – 3 setose medially, article 4 with large apical robust seta.

Pereon ( Fig. 9 ). Gnathopod 1 slender; coxa ventral margin with several short setae; basis short, with single long seta on posterior margin and several setae on posterodistal margin; merus setose posteriorly; carpus longish trapezoidal, posterior margin and medial surface heavily setose; propodus longish ovate, about 0.85 times as long as carpus, anterodistal corner and anteromedial surface setose, palm oblique, defined by single robust seta; dactylus slender, slightly curved posteriorly. Gnathopod 2 asymmetrical, carpus–dactylus different between right and left; coxa subtrapezoidal, ventral margin with several setae, gill large, oval, subequal to basis length; basis posterior margin bearing many long or short setae, lateral surface with ridge; merus with acute posterodistal spine; right carpus short, lobate and setose posterodistally; right propodus longish ovate, length about 2.1 times width, palm strongly oblique, posterior margin distally with triangular and small trapezoidal projections bearing 3 lateral and 4 medial, and 3 lateral and 2 medial robust setae, respectively, middle to proximal parts smooth, posteromedial surface with 2 large and many short robust setae; right dactylus stout, strongly curved posteriorly; left carpus much longer than right one, heavily setose posterodistally; left propodus slender, about 1.9 and 0.55 times as long as carpus and right propodus, respectively, length about twice of width, anterodistal corner and posterior margin setose, palm oblique, defined by tiny projection with long robust seta, posterior margin bearing many marginal and 2 medio-submarginal robust setae; left dactylus slender.

Pereopods 3–4 subequal in shape, pereopod 3 about 1.1 times length of pereopod 4; coxae subtrapezoidal, ventral margins with a few short setae, gills large; bases rectilinear, anterior and posterior margins with 3 and 5 long setae, respectively; meri – propodi with marginal robust setae; dactyli short. Pereopod 5 about 1.3 times length of pereopod 4; coxa with several short setae on ventral margin; basis subrectangular, length about 1.65 times width (excluding posterodistal lobe), posteroproximal corner projected, posterodistal corner roundly lobed, anterior margin bearing short robust setae, anterodistal corner with long robust seta, lateral surface with ridge; merus – propodus with marginal robust setae, dactylus short. Pereopod 6 about 1.3 times as long as pereopod 5; coxa with 2 robust setae on anteroventral margin; basis subrectangular, length about 1.45 times width (excluding posterodistal lobe), posterodistal corner roundly lobed, anterior margin bearing short robust setae, anterodistal corner with long robust seta, lateral surface with ridge; merus – propodus with marginal robust setae, dactylus short. Pereopod 7 slightly shorter than pereopod 6; coxa with robust seta on anteroventral margin; basis subrectangular, length about 1.4 times width (excluding posterodistal lobe), posterodistal corner roundly lobed, anterior margin bearing short robust setae, anterodistal corner with long robust seta, lateral surface with ridge; merus – propodus with marginal robust setae, dactylus short.

Pleon ( Figs 7 , 10 ). Pleonites 1–3 lacking dorsal teeth; epimeron 1 bearing 1 posteroventral and 1 ventral teeth and lateral ridge; epimeron 2 with 1 posteroventral and 1 ventral teeth, 2 ventral robust setae and lateral ridge; epimeron 3 with 1 posterior, 1 large posteroventral and 2 ventral teeth and 4 ventral robust setae. Urosomites 1–3 also lacking dorsal teeth. Pleopods 1–3, pleopod 3 shortest; peduncles with a few proximal short setae, 2 coupling hooks and 2 short setae distally; outer rami slightly shorter than inner rami, outer rami with 17, 17, 14 articles and inner rami with 16, 16, 14 articles respectively. Uropod 1, peduncle with large basofacial and distolateral robust setae and 6 dorsolateral and 6 dorsomedial (distal one large) robust setae; outer ramus slightly shorter than inner ramus, about 0.65 times as long as peduncle, with 2 lateral, 3 medial and 4? terminal robust setae; inner ramus with 3 lateral, 4 medial and 5 terminal robust setae. Uropod 2 about 0.65 times length of uropod 1; peduncle bearing 4 dorsolateral and 2 dorsomedial robust setae, mediodistal corner with 2 robust setae dorsally; outer ramus about 0.9 times length of inner ramus, slightly shorter than peduncle, with 4 lateral, 3 medial and 5 terminal robust setae; inner ramus with 2 lateral, 6 medial and 5 terminal robust setae. Uropod 3 about 2.35 times as long as uropod 2; peduncle projected proximally, lateral surface with 2 dorsodistal and 3 ventrodistal robust setae, medial surface bearing 4 dorsal and 2 distal robust setae; outer ramus oblong, a little widened distally, length about 3.5 times width, slightly longer than inner ramus, about 2.55 times length of peduncle, ventral margin serrate, with many bundles of robust setae, dorsal margin almost smooth, bearing several single robust setae; inner ramus situated dorsally on outer ramus, longish elliptical, length about 3.0 times width, medioproximal surface with ridge for restraining outer ramus, ventral margin smooth, with a few robust setae distally, dorsal margin also smooth, with several robust setae. Telson about 1.2 times longer than wide; each distal end with 1 long and 1 short robust setae and sensory seta, each lateral margin bearing 2 sensory setae.

Variation. Gnathopod 2. Female, 7.4 mm (OMNH-Ar-11278, Fig. 10 F-G2): symmetrical, coxa longish subtrapezoidal, other parts similar to smaller gnathopod 2 of male, 6.9 mm (OMNH-Ar-11275); medium-sized male, 6.1 mm (OMNH-Ar-11276): asymmetrical, similar to both gnathopods 2 of male, 6.9 mm, but palmar projections of larger gnathopod 2 smaller, left propodus about 0.6 times as long as right propodus; small male, 4.6 mm (OMNH- Ar-11277; Fig. 10 SM-LG2, RG2): shape symmetrical, similar to smaller gnathopod 2 of male, 6.9 mm, but right propodus about 0.8 times longer than left one. Pleonal epimera 1–3 ( Table 3 ), numbers of teeth and robust setae with little variation. Telson , number of robust setae with no variation.

Coloration in recently fixed specimen ( Fig. 11 ). Eyes dark brown, body and appendages whitish, pale yellow internal organs seen through.

Remarks. Morphological characters of the present specimens quite agree with the original description and figures of Ceradocus laevis from Philippines ( Oleröd 1970) except for 3 posterior teeth on the epimeron 3 (1–2 teeth in the present specimens, see Table 3 ). This species closely resembles C. woorree from Australia; however, the latter species has the rounded anteroventral corner of the gnathopod 1, the narrower bases of the pereopods 5–6, the epimera 1–3 without posterior and ventral teeth, and the telson lobes each with 1 long and 2 short robust setae ( Berents 1983).

Habitat in Japan. Dead coral and fine sand bottom, intertidal to 0.5 m depth .

Distribution. Japan: Okinawa Island and Iriomote Island in Okinawa Prefecture (present study); China: Hainan Island ( Ren 2012); Philippines: Mindoro ( Oleröd 1970); Vietnam: Khánh Hòa, Bà R ịa-Vũng Tàu and Kiên Giang Provinces ( Dang & Le 2011); Singapore: Pulau Ubin ( White 2015).

Figures

FIGURE 1. Map showing collecting sites of the examined specimens. A, Yura Town in Wakayama Prefecture; B, Awase, Okinawa Island in Okinawa Prefecture; C, Iriomote Island in Okinawa Prefecture.

FIGURE 7. Ceradocus laevis Oleröd, 1970. Male, 6.9 mm (OMNH-Ar-11275). Habitus and dorsal views of pleonites and urosomites.

FIGURE 8. Ceradocus laevis Oleröd, 1970. Male, 6.9 mm (OMNH-Ar-11275). Scales: 0.05 mm.

FIGURE 9. Ceradocus laevis Oleröd, 1970. Male, 6.9 mm (OMNH-Ar-11275). Scales: 0.2 mm.

FIGURE 10. Ceradocus laevis Oleröd, 1970. All except for M, F and SM, male, 6.9 mm (OMNH-Ar-11275); M, male, 6.9 mm (OMNH-Ar-11279); F, female, 7.4 mm (OMNH-Ar-11278); SM, small male, 4.6 mm (OMNH-Ar-11277). Scales: 0.1 mm.

FIGURE 11. Ceradocus laevis Oleröd, 1970. Large male collected together with males, 6.9 and 6.1 mm (OMNH-Ar-11275, 11276). Fixed specimen (2 hours after fixation).