Caviallianassa riwo, Poore, 2023

Poore, Gary C. B., 2023, New records, one new genus and 21 new species of Callianassidae (Crustacea, Axiidea) from the Indo-West Pacific, Memoirs of Museum Victoria 82, pp. 167-255 : 185-187

Caviallianassa riwo sp. nov.

http://zoobank.org/urn:lsid:zoobank.org:act:24234C2A-B2AE-

4D64-BB50-F11D8849A930

Figures 13 , 14

Caviallianassa PNG-1172.— Robles et al., 2020: figs 1, 3, 6.

Material examined. Holotype. Papua New Guinea, Madang, off Riwo , 5° 9' S, 145° 48.2' E, 1–2 m ( PAPUA NIUGINI stn PR235), MNHN IU-2013-7111 *# (female, 2.5 mm).

Description. Female. Rostrum triangular, blunt, flat, situated level with dorsal carapace, shorter than half length of eyestalks. Carapace dorsally flat, 0.8 length of pleomeres 1–2 combined; orbital margin almost transverse, with pair of semicircular translucent area laterally; anterolateral lobes produced, rounded; subanterolateral margin straight; anterior margin of branchiostegite with dorsal concavity; cervical groove across 0.75 length of carapace, reaching linea thalassinica. Thoracic sternite 7 subpentagonal with slightly projecting anteromedian margin; ventral surface with shallow median groove. Pleomere 1 tergite with transverse groove, posterior half scarcely wider than anterior half. Pleomere 2 about as long as wide. Pleomeres 3–5 each wider than long; pleura each with patch of plumose setae. Pleomere 6 0.9 times as long as wide, 1.8 times as long as pleomere 5, with slight posterolateral notch.

Eyestalk about 1.3 times as long as wide, with dorsal face close to rostrum, anterolateral margin tapering, convex, oblique, anteromedial angle rounded in dorsal view, overreaching distal margin of antennular peduncle article 1. Cornea densely pigmented, occupying anterolateral margin of eyestalk.

Antennular peduncle reaching beyond distal margin of antennal peduncle; article 1 not visible in dorsal view; article 3 little longer than articles 1 and 2 combined; articles 2 and 3 with longitudinal ventral row of long setae. Antennal peduncle article 5 0.7 times as long as article 4; scaphocerite minute, droplet-shaped.

Maxilliped 3 ischium dilating distally, 1.3 times as wide as long, crista dentata consisting of row of 9 small, well spaced teeth; merus 0.6 times as long as ischium measured along outer margin, about twice as wide as long, with mesiodistal margin produced as convex lobe beyond base of carpus; carpus 0.8 times as long as merus outer margin; propodus tapering over distal two-thirds, 1.2 times as long as wide, flexor (inner) margin with subproximal lobe; dactylus 0.8 times as long as propodus, with convex extensor (outer) margin, densely setose distally, with straight flexor (inner) margin bearing 4 setae.

Pereopods 1 (chelipeds) unequal, dissimilar. Major cheliped massive, carpus-palm upper margin 1.25 carapace length. Ischium expanding distally, upper margin concave, unarmed; lower margin with 3 teeth. Merus as long as ischium, 1.75 times as long as wide (tooth excluded), ovate; upper margin convex, carinate, with subproximal tubercle; lower margin with 2 subproximal teeth, with broad lobe beyond midpoint. Carpus 1.2 times as wide as long; margins carinate; upper margin smooth; lower margin convex. Propodus upper margin 1.5 times as long as carpus; palm widest subproximally, tapering, 1.1 times as long as wide; upper margin carinate; lateral surface smooth, convex, with concave gape, with cluster of long setae close to distal margin; mesial surface convex, with lobed ridge set back from distolateral margin; lower margin sharply carinate, with row of setae extending onto fixed finger; fixed finger 0.5 times as long as palm, curved upwards; cutting edge, concave, smooth. Dactylus overreaching fixed finger, strongly hooked distally; upper margin with tufts of long setae; lateral surface with few tufts of long setae along cutting edge; cutting edge with 2 large blunt teeth.

Minor cheliped carpus-palm upper margin 1.05 carapace length. Ischium upper margin smooth, lower margin with 1 small spine. Merus 0.8 times as long as ischium; margins smooth. Carpus parallel-sided over most of length, 1.3 times as long as merus, 2.3 times as long as wide. Palm rectangular, 1.4 times as long as wide; upper margin barely convex; lower margin carinate, with row of long setae extending onto fixed finger. Fixed finger triangular, 0.6 times as long as palm, cutting edge denticulate over middle third. Dactylus as long as palm, curved; cutting edge smooth.

Pereopod 2 merus lower margin slightly sinusoidal, 2.15 times as long as wide; carpus 1.5 times as long as wide; chela subtriangular; palm twice as wide as upper margin; dactylus twice as long as palm upper margin. Pereopod 3 carpus subtriangular, 1.8 times as long as wide; propodus almost semicircular, wider than long, with strongly produced evenlycurved lower margin, marginal setae clustered, with 1 slender spiniform seta; dactylus about as long as propodus upper margin. Pereopod 4 coxa flattened ventrally, immovable; merus 1.25 times as long as ischium; carpus as long as merus; propodus 0.8 times as long as carpus, with dense grooming setae distally on lower margin, scattered stiff setae on outer surface, with long spiniform setae parallel to dactylus, almost reaching tip; dactylus half as long as propodus. Pereopod 5 slender, with chela about as long as carpus, slightly curving, fixed finger with short subdistal spiniform setae.

Pleopod 1 of 2 articles; ramus shorter than peduncle, with 2 distal setae. Pleopod 2 biramous; peduncle bent; exopod 0.7 times as long as endopod; endopod of 2 articles. Pleopods 3–5 biramous, endopod 1.5 times as long as wide; appendix interna twice as long as wide, projecting well beyond mesial margin of endopod, bearing coupling hooks on apical margin.

Uropod endopod and exopod overreaching posterior margin of telson. Endopod oval, widest proximally, about as long as wide; upper surface with 1 long spiniform seta; anterior margin slightly convex; margins setose. Exopod widest at midpoint, 1.3 times as long as wide, exceeding endopod by abut half its length; anterior margin concave; posterior margin with 6 or 7 blade-like setae indistinguishably merged with distal margin; upper surface without setae; dorsal plate extending about halfway across exopod, comprising about 30 stiff setae merging anteriorly with similar setae on distal margin.

Telson trapezoidal, 1.4 times as wide as long, broadest at anterior third, narrowing posteriorly to evenly rounded posterolateral corners; posterolateral angle with 2 short spiniform setae; posterior margin with median tooth.

Etymology. From Riwo, Papua New Guinea, a village near the type locality (noun in apposition).

Distribution. Eastern Coral Triangle ( Papua New Guinea); 1– 2 m.

Remarks. The species is known from a single female well separated from Caviallianassa moorea in Robles et al.’s (2020) molecular phylogram. The antennae are relatively more compact than in C. moorea . Although the female is smaller than those of C. moorea , the major cheliped has more developed dentition on the fingers; the bifid meral tooth is more prominent than the two small teeth seen in C. moorea , approaching that seen in C. cavifrons (Komai and Fujiwara, 2012) .

Figures

Figure 13. Caviallianassa riwo sp. nov. Papua New Guinea. MNHN IU-2013-7111, holotype female, 2.5 mm: a, carapace, pleon, telson, uropod; b, carapace, pleomeres 1, 2; c, d, antennular, antennal peduncles, eyestalks, carapace front; e, pleomere 6, right lateral; f, telson, right uropod, left uropod endopod; g, maxilliped 3; h, major (left) cheliped; i, major cheliped fingers, lateral; j, minor (left) cheliped. Scale bars = 1 mm.

Figure 14. Caviallianassa riwo sp. nov. Papua New Guinea. MNHN IU-2013-7111, holotype female, 2.5 mm: a–c, pereopods 2–4; d–f, pleopods 1–3. Scale bar = 1 mm.