Cymadusa imbroglio Rabindranath, 1972

[New Japanese name: Sen-nuki-hige-naga]

(Figs 2–8)

Cymadusa imbroglio Rabindranath, 1972: 175, fig. 9.— Myers, 1985: 29, figs 20–21.— Myers, 1995: 38.— Myers, 1997: 108.—

Ortiz & Lalana, 1997: 106. — Peart, 2004: 320, figs 12–15.— Peart, 2007: 18, figs 12–14.— Hughes & Lowry, 2009:

184–188, figs 19–20, pl. 1F. — Hughes & Peart, 2013: 52, fig. 29. Cymadusa filosa forme imbroglio .— Ledoyer, 1984: 5, 15 figs 5–6. Ampithoidae spp. [including Cymadusa imbroglio and other ampithoid species]— Nakamoto et al., 2018a: 57, 58.— Nakamoto et al., 2018b: Table S2. Ampithoidae sp.— Kodama et al., 2024: Fig. 2, Table S4.

Material examined. All the specimens were collected from seagrass-seaweed mixed beds in Ishigaki Island, Japan. NSMT-Cr 32434, 1 full-grown male, 12.6 mm (voucher specimen for the new Japanese name); NSMT-Cr 32435, 1 full-grown male, 13.1 mm; NSMT-Cr 32436, 1 male, 11.6 mm; NSMT-Cr 32437, 1 male, 11.8 mm; NSMT-Cr 32438, 1 ovigerous female, 12.6 mm; NSMT-Cr 32439, 1 ovigerous female, 11.3 mm, Nagura Bay, Ishigaki Island, Japan, 24°23’ 23”N, 124°08’ 05”E, intertidal seaweed-seagrass mixed bed, on 11 May 2015, coll. Kenta Nakamoto. NSMT-Cr 32440, 1 full-grown male, 13.1 mm; NSMT-Cr 32441, 1 immature male, 9.7 mm; NSMT-Cr 32442, 1 ovigerous female, 12.2 mm, Arakawa, southwest coast of Ishigaki Island, Japan, 24°21’27.0”N, 124°07’19.2”E, intertidal seaweed-seagrass mixed beds, on 19 May 2022, coll. Hideaki Yamada and Iwao Tanita. NSMT-Cr 32443, 1 ovigerous female, 11.3 mm; NSMT-Cr 32444, 1 immature male, 7.3 mm; NSMT-Cr 32445, 1 female, 8.8 mm, Arakawa, southwest coast of Ishigaki Island, Japan, 24°21’23.8”N, 124°07’22.4”E, intertidal seaweed-seagrass mixed beds, on 19 May 2022, coll. Hideaki Yamada and Iwao Tanita.

Description of male. Based on male, 12.6 mm, NSMT-Cr 32434.

HEAD. Head as long as deep. Antenna 1 (Fig. 2, 3A) longer than antenna 2; peduncular article 1 with distomedial robust seta, peduncular articles 2 and 3 setose but with no robust setae; primary flagellum with 53 articles, distinctively longer than flagellum of antenna 2; accessory flagellum (Fig. 3B) with 1 article, with 2 subdistal setae and 2 distal setae. Antenna 2 (Fig. 2, 3A) peduncular article 3 with 1 dorsal robust seta and 1 ventral small robust seta; flagellum with 33 articles.

Mouth parts. Upper lip (Fig. 3D) distal margin setulose, posterior surface setulose with subtriangular process. Lower lip (Fig. 3E) outer plates notched, forming a medial excavation; mandibular lobe well developed, rounded apically. Mandible (Fig. 3F–H), molar well developed, triturating, accessory setal row with 8 serrulate setae; palp with 3 articulate; article 1 shorter than article 2; article 2 slightly shorter than article 3 with distomedial seta; article 3 longer than article 1 with setae in distal half of medial margin; left and right incisor 7- and 8-dentate, respectively; left and right lacinia mobilis 6- and 6-dentate, respectively. Maxilla 1 (Fig. 3I) inner plate with 4 setae; outer plate truncate with distal 10 dentate setae; palp article 2 broad, distomedial margin with row of 10 robust setae, ventral surface with subdistal row of 5 setae. Maxilla 2 (Fig. 3J) inner plate narrower than outer plate. Maxilliped (Fig. 3K) outer plate with row of large robust setae along medial margin.

PEREON. Coxae 1–5 deeper than broad, coxae 6–7 broader than deep. Gnathopod 1 (Fig. 4A) smaller than gnathopod 2; coxa distinctly larger than coxa 2, anteroventrally produced, anterior margin convex, anteroventral corner rounded, posteroventral corner rounded with several setae, ventral margin with setules; basis subequal in length to coxa, anterodistal lobe weakly developed; merus posterodistal lobe subacute with several setae; carpus about 2 times as long as broad, subequal in length to propodus, anterodistal corner with slender setae, posterior margin weakly rounded, rather straight; propodus broad; palm with excavation, with 1 robust seta defining palm; dactylus long, beyond palm-defining robust seta of propodus, inner margin with micro-serration with setules. Gnathopod 2 (Fig. 4B) coxa ventral margin rounded with setules, posteroventral margin with several slender setae; basis with sparse slender setae on posterior margin, anterodistal lobe small, rounded, not reaching beyond ischium, anterodistal corner without setae; ischium with anterodistal small lobe, lobe slightly more angular than that or basis; carpus much shorter than propodus, subtriangular, posteriorly with densely setose carpal lobe; propodus broad, less than 1.5 times as long as broad, not produced into anterodistal lobe; palm transverse, excavate, with midmedial subquadrate projection, without palm defining robust setae; dactylus shorter than palm, inward curved, inner margin with micro-serration with setules. Pereopods 3 and 4 similar in shape (Fig. 4C, D), simple; coxae, subquadrate, ventral margin with small setules, medial surface with slender setae, posteroventral corner with a group of slender setae, coxa 4 larger than coxa 3; basis narrow, posterior margin with turfs of long slender setae, anterior margin with sparse long slender setae in proximal half; merus subequal in length to carpus, broader than carpus, anterodistal corner weakly produced; dactylus tapering, weakly curved. Pereopod 5 simple (Fig. 5A), coxa bilobate, anterior lobe strongly enlarged, subquadrate, anteroventral and posteroventral corner rounded, ventral margin slightly convex with setules, medial surface with slender setae, posterior lobe small, with several short setae; basis expanded, without medial slender setae, anterior margin with row of short robust setae, posterior margin without robust setae; propodus not expanded distally, with robust setae on flexor margin; dactylus falcate. Pereopod 6 (Fig. 5B) coxa smaller than coxa 5, bilobate, anterior lobe deeper than posterior lobe, posterior lobe with slender setae; basis-dactylus larger than pereopod 5; basis not expanded as in pereopod 5, with several robust setae on distal 1/3 of anterior and posterior margins; propodus not expanded distally, with robust setae on flexor margin; dactylus falcate. Pereopod 7 (Fig. 5C) similar to pereopod 6, but coxa semicircular, basis-dactylus slightly larger than pereopod 6, posteroproximal corner of basis more angular.

PLEON. Epimeral plate 1 (Fig. 6A) rounded ventrally, posteroventral corner with faint notch bearing small seta. Epimeral plate 2 rounded ventrally, larger than epimeral plate 1, anterior margin excavated, posteroventral corner slightly more angular than that of epimeral plate 1, with faint notch bearing small seta. Epimeral plate 3 subquadrate, larger than epimeral plate 2, anteroventral corner rounded, posteroventral corner with faint notch bearing small seta. Uropod 1 (Fig. 6B) peduncle with 5 dorsolateral and 7 dorsomedial robust setae, with ventrolateral row of slender setae, with large acute distoventral projection; outer ramus slightly shorter than peduncle (distoventral peduncular projection ignored) with rows of dorsolateral and dorsomedial robust setae, with apical robust setae; inner ramus about 1.1 times as long as outer ramus, with rows of dorsolateral and dorsomedial robust setae, with apical robust setae. Uropod 2 (Fig. 6C) peduncle with 3 medial and 2 lateral robust setae, with small acute distoventral projection; outer ramus slightly longer than peduncle with rows of dorsolateral and dorsomedial robust setae, with apical robust setae; inner ramus slightly longer than outer ramus, with rows of dorsolateral and dorsomedial robust setae, with apical robust setae. Uropod 3 (Fig. 6D) peduncle longer than broad, less than 2 times as length as rami, lateral margin with a few setae, distal margin with 3 dorsolateral robust setae, 2 dorsomedial robust setae, several ventral slender setae; outer ramus subequal or slightly shorter than inner ramus, with 2 large recurved distal robust setae, with 1 proxiolateral robust seta and 5 lateral slender setae; inner ramus with apical slender setae, 3 apical robust setae, 2 lateral robust satae. Telson (Fig. 6E) subtrapezoidal, apically truncated, with small apicolateral cusp on each distolateral corner, with 2 pair of medial slender setae, with sparse dorsolateral setae.

Description of female. Generally similar to males except for gnathopods and oostegites. Gnathopod 1 (Fig. 7A), similar to that of males except for following points: coxa enlarged, anteriorly produced, anterodistal corner rounded, anterior margin concave; basis baring several groups of long slender setae on medial surface; carpus shorter than that of males; propodus palm convex. Gnathopod 2 (Fig. 7B), distinctively smaller than that of full-grown males (Fig. 8C), but similar to that of small males (Fig. 8A): coxa deeper than wide; propodus smaller, palm oblique, sinuous, well defined bearing a spine, midmedial projection of palm unrecognizable. Oostegites, present on gnathopod 2 and pereopod 3–5, each oostegite broad.

Variations. Antenna 1 flagellum increases number of articles in relation to body size, in the range of 23–54 in our specimens except for individuals with the terminal part of the antennae missing. Antenna 2 flagellum also increases number of articles in relation to body size, in the range of 19–38 in our specimens except for individuals with the terminal part of the antennae missing. Number of robust setae in uropods varies individually. Male gnathopods 2 show ontogenetic morphological change. In small males (Fig. 8A), the midmedial projection of gnathopod 2 palm is unrecognizable, and the palm is oblique, sinuous, well defined, and bearing a spine. In medium sized males (Fig. 8B), the midmedial projection of gnathopod 2 palm is distinct, large, and broad, and the palm is slightly oblique without robust setae. In large full-grown males (Fig. 8C), the midmedial projection of gnathopod 2 palm is distinct, small, and narrow, the palm is more transverse without robust setae, and the dactylus is more curved (Fig. 8C).

Coloration. Body (Fig. 9) generally yellowish brown with dark brown dots and mottling; eyes red; peduncular articles of antennae distally white; in large males, propodus and dactylus of gnathopod 2 proximally white.

Distribution. This species is widely distributed in the Indian Ocean and West Pacific (Fig. 1).

Indian Ocean. India: Gulf of Mannar in Manoli Island (Rabindranath 1972; Type locality). Mozambique Channel? (Not mentioned in text but shown in Map 1 in Peart 2004). Australia: Cocos (Keeling) Islands (Hughes & Pear 2013); Western Australia (Peart 2004); Timor Sea (Hughes & Peart 2013).

Pacific Ocean. Australia: Grafton, New South Wales (Hughes & Pear 2013); Botany Bay, New South Wales (Peart 2004, 2007); Lord Howe Island, New South Wales (Hughes & Pear 2013); Western Port, Victoria (Hughes & Pear 2013); Lizard Island, Queensland (Hughes & Lowry 2009); Tasmania (Peart 2004; detailed locality unknown). Micronesia: Kosrae (Myers 1995). Western Samoa (Myers 1997). Fiji: Momi Bay; Nasese; Mburelevu; Nananui Ra (Myers 1985). New Caledonia: Récif Abore (Ledoyer 1984). Japan: Ishigaki Island (this study).

Molecular data. Sequences of COI were determined from one large male (NSMT-Cr 32440; INSDC, LC847186, 678 bp) and one ovigerous female (NSMT-Cr 32443; INSDC, LC847187, 623 bp) specimens.

Remarks. The present species Cymadusa imbroglio was originally described by Rabindranath (1972) from the Gulf of Manaar in southeastern India. After the original description, several authors provided redescriptions and/or illustrations, based on the specimens from a wide area in the Indo-Pacific (Ledoyer 1984, Myers 1985, Peart 2004, 2007, Hughes & Lowry 2009, Hughes & Peart 2013). In these previous records, significant morphological difference has been pointed out between the Indian Ocean population and the Pacific Ocean population (e.g., Peart 2004, 2007, Hughes & Lowry 2009), such as the length of the antenna 2 flagellum, the shape of the carpus of male gnathopod 1, the shape of the palm of male gnathopod 2, the number of distal robust setae on the peduncle of uropod 3, and the length of the outer ramus of uropod 3. Peart (2007) considered that the Indian and Pacific Ocean populations might not be conspecific. Hughes & Lowry (2009) however indicated that morphological changes with growth stages encompasses the previously known variation, and thus considered their conspecificity. Our specimens at hand have (1) the antenna 2 with distinctively shorter flagellum than that of antenna 1, (2) the male gnathopod 1 carpus with weakly rounded (or rather straight) posterior margin, and (3) the uropod 3 outer ramus slightly shorter than inner ramus, which clearly show a similarity with the characters of Pacific Ocean population. Since any sequence data has not been obtained from the Indian Ocean populations to date, species continuity cannot be verified by molecular methods in this study. The COI sequence data from Japanese population provided in this study will be helpful in examining the conspecificity of this species in future.

Myers (1985) suggested the similarity of C. imbroglio to C. microphthalma (Chevreux, 1901), and implied the possibility that this species may be a synonym of C. microphthalma . He reserved his conclusion because only females were obtained for the species C. microphthalma . Subsequently, however, Ren (2001, 2006) treated the Myers’ (1985) material as C. microphthalma . In another study, Ledoyer (1982) noted that C. filosa is also very close to C. microphthalma . Ledoyer’s material was later accepted as C. ledoyeri by Peart (2004). Peart (2004) also noted the difficulty in identifying C. microphthalma . This confusion about C. microphthalma was caused by the fact that only female individuals were described in the original description by Chevreux (1901). After the original description, Walker (1905), Sivaprakasam (1970), and Ren (2006) provided descriptions and illustrations of male specimens of ‘ C. microphthalma ’ from Maldives, India and China, respectively. However, it is unclear whether the specimens examined in the studies were true C. microphthalma . We generally agree with the similarity of C. imbroglio to C. microphthalma . However, we consider that the taxonomic identity of C. microphthalma is still vague at this stage, and thus the taxonomic treatment of C. microphthalma is retained in this study.