(figures 20–22)

Cymadusa vadosa Imbach, 1967: 89–90, pl. 32; Poore and Lowry, 1997: 900.

Cymadusa filosa: Ledoyer, 1984: 15–18, figures 5, 6 (as Group I smooth).

Material examined. MNHN, male, 8 mm in length, Noumea, New Caledonia, 22°9.6∞S, 166°16.2∞E, collected by M. Ledoyer.

Type locality. Bay of Nha-Trang, Vietnam, South China Sea.

Diagnosis. Antenna 1 with a two-articulate accessory flagellum. Antenna 2 with weakly setose margins. Gnathopod 1 merus produced to form a small, rounded anteroventral lobe; carpus broad and short, subtriangular. Gnathopod 2 propodal palm not defined by posterodistal tooth, with no mid-palmar tooth; dactylus subequal to palm.

Description

Based on male, 8 mm in length.

Head. Antenna 1 longer than antenna 2; peduncular article 1 shorter than article 2, article 2 longer than article 3, article 3 shorter than article 1; primary flagellum incomplete but with at least seven articles; accessory flagellum with two articles. Antenna 2 weakly setose on ventral margin; peduncular article 4 subequal to article 5. Lower lip outer plate outer lobe longer than inner lobe. Mandible molar setal row with eight robust setae; palp article 1 shorter than article 2, article 2 shorter than article 3, article 3 longer than article 1; long plumose setae on posterior margin and apex of article 3. Maxilla 1 inner plate with five plumose setae. Maxilliped setose.

Pereon. Gnathopod 1 subequal to gnathopod 2; poorly setose; coxa produced forward, anterior margin straight, ventral margin with just a tuft of a few simple setae on posterior corner; basis subequal to the coxa, without long plumose setal fringe, distal lobe present; merus produced to form a short, subacute anteroventral lobe; carpus longer than merus, subequal to propodus, divergent at distal end, subtriangular; carpal lobe rounded; propodus ovoid; palm entire, convex, defining posterodistal tooth absent, mid-palmar tooth absent; dactylus longer than palm. Gnathopod 2 weakly setose; coxa ventral margin with a tuft of simple setae on posterior corner; basis subequal in length to coxa, no setal fringe, distal lobe present; merus produced to form a small, rounded anteroventral lobe; carpus subequal to merus, shorter than propodus; propodus subquadrate; palm entire, slightly concave, defining posterodistal tooth absent, mid-palmar tooth absent; dactylus tapering evenly.

Pereopods 3 and 4 similar in shape; coxae without setae. Pereopod 5 coxae without setal fringe and medial setae. Pereopod 6 basis with sparse medial setae. Pereopod 7 basis subrectangular. Pereopods 6 and 7 much longer than pereopods 3–5; distal articles with sparse setae.

Pleon. Epimeron 3 subquadrate, with a small, subacute posterodistal tooth. Uropod 1 peduncle with 10 marginal robust setae; outer ramus longer than inner ramus. Uropod 2 outer ramus longer than inner ramus. Uropod 3 with three distal peduncular robust setae; outer ramus shorter than inner ramus, hooks both strongly recurved, setal fringe absent on lateral margin; inner ramus with both robust and slender setae. Telson truncated, with lateral and apical slender setae (not in oblique rows); apical cusps present.

Variation. Based on the above-documented animal, however, there is some leftright dimorphism present. This is probably just an artefact, most likely the gnathopod is damaged. Left gnathopod 2 weakly setose; coxa ventral margin with a tuft of simple setae on posterior corner; basis subequal in length to coxa but no setal fringe; merus produced to form a small, subacute anteroventral lobe; carpus subequal to merus, shorter than propodus; propodus subquadrate; palm entire, convex, defined by a small, subacute posterodistal tooth, mid-palmar tooth absent; dactylus subequal in length to palm, tapering evenly.

Remarks

Ledoyer, 1984 recorded this species as a form of Cymadusa filosa that most closely resembles Cymadusa vadosa. Both records are around 8 mm in length (Imbach’s is 8.5 mm) and are therefore easy to contrast. When compared to Imbach’s original description from Bay of Nha-Trang, Vietnam there are only a few differences. These include article 1 of antenna 1 subequal in length to article 2 in Imbach’s animals and shorter than article 2 in Ledoyer’s animal; accessory flagellum of antenna 1 with one long article in Imbach’s animal compared to two articles (Ledoyer’s animal); uropod 3 with more robust setae on the peduncle and inner ramus than on Ledoyer’s animal; epimeron 3 more rounded on Imbach’s animal than on Ledoyer’s animal.

These differences are slight enough to be variations of the same species. Interestingly, Ledoyer (1984) reported that there was left–right side dimorphism on the gnathopod 2 (noted in detail in the description). This could be just an artefact or damage as this type of dimorphism has not been recorded before in the family Ampithoidae.

Habitat. Cymadusa vadosa occurs on seagrasses.

Distribution. Bay of Nha-Trang, Vietnam, South China Sea; New Caledonia (Map 1).