Riwo zeidleri, Hughes, L. E. & Lowry, J. K., 2015

Hughes, L. E. & Lowry, J. K., 2015, Two new species of Lysianassidae Dana, 1849 from Australia: Riwo zeidleri and Socarnella delectabilis (Crustacea: Peracarida: Amphipoda), Zootaxa 3936 (1) : -

Riwo zeidleri sp. nov.

( Figs 1 , 2 )

Type material. Holotype, female, 4.1 mm, dissected, 3 slides, SAMA C 8391, 200 m offshore, north point of Marum Island, Sir Joseph Banks Group, South Australia (34°31’S 136°15’E), 6 m, on sponge and under rocky reef, 11 January 1984, coll. W. Zeidler (SAM-14); paratypes 5 specimens (inc. male 2.4 mm), SAMA C8392, same location as holotype.

Type locality. 200 m offshore, north point of Marum Island, Sir Joseph Banks Group, South Australia (34°31’S 136°15’E).

Etymology. Named for Wolfgang Zeidler, the collector of the species, in appreciation for his elucidating studies of hyperiidean amphipods.

Description. Holotype female, 4.1 mm, SAMA C8391; paratype male, 2.4 mm, SAMA C8392. Colour whitish with small black chromatophores covering pereon, coxae and epimera, but concentrated anteriorly on pereon segments to give a striped effect; body without setae.

Head as deep as long; lateral cephalic lobe large, broadly rounded; rostrum small; eyes subovate, black. Antenna 1 medium length, 0.3 × body; peduncular article 1 short, length 1.1 × width; article 2 short, 0.25 × article 1; article 3 short, 0.2 × article 1; accessory flagellum long, 0.4 × primary flagellum, 5-articulate, article 1 subequal to article 2 length; flagellum 9-articulate, callynophore weak 1-field, without posterodistal slender or robust setae, without flagellar robust setae, calceoli absent. Antenna 2 subequal in length to antenna 1; peduncle with brush setae present, strongly geniculate between peduncular articles 3–4; article 3 long, 0.8 × article 4; peduncular articles 4–5 not enlarged; flagellum 8-articulate, calceoli absent. Mouthpart bundle: subquadrate. Labrum epistome concave, separate from upper lip; upper lip produced, rounded. Mandible incisors symmetrical, large, with convex margins; lacinia mobilis absent; accessory setal row without distal setal tuft, left and right rows each with 3 long, slender, multiserrate robust setae; molar developed as small, smooth setose flap; mandibular palp attached proximally, article 1 short, length 1.1 × width; article 2 elongate, slender, length 4.3 × width, 1.8 × article 3, with 5 posterodistal A2-setae; article 3 slender, blade-like, long, length 3 × width, without A3- or B3-setae, with 1 proximal and 2 distal D3-setae on posterior margin, and 2 apical E3-setae. Maxilla 1 inner plate narrow with 1 simple apical seta (broken); outer plate with 10 setal-teeth in modified 6/5 arrangement; palp large, 2-articulate, with 7 short terminal conate setae and 1 subterminal seta, distomedial margin not serrate. Maxilla 2 inner and outer plates broad, subequal in length. Maxilliped inner plate large, subrectangular, with 3 apical nodular setae, oblique setal row reduced with 2 setae; outer plate small, subrectangular, without apical slender or robust setae, 8 vestigial medial robust setae; palp large, 4-articulate; article 2 broad, length 2.9 × width, 1.1 × article 3; article 3 long, slender, length 2 × width; dactylus well-developed, with 1 subterminal seta, unguis present.

Pereon. Oostegites from gnathopod 2 to pereopod 5. Gills from gnathopod 2 to pereopod 7, not pleated. Gnathopod 1 simple; coxa large, 0.9 × coxa 2, anterior margin straight, anteroventral corner weakly produced, subquadrate, posterior margin straight; basis long, slender, length 2.6 × width, anterior margin smooth, without setae; ischium short, length 1.1 × width; merus, posterior margin with patch of short setae and a few simple slender setae; carpus subrectangular, short, length 1.9 × width, subequal in length to propodus, without denticulate patch near posterodistal margin; propodus small, subrectangular, length 2.1 × width, tapering distally, posterior margin smooth, straight, with few slender setae, without denticulate patch near posterior margin, palm absent; dactylus simple, without subterminal spine. Gnathopod 2 minutely subchelate; coxa large, subequal in size to coxa 3; ischium long, length 3.1 × width; carpus long, length 2.4 × width, posterior margin straight; propodus subrectangular, short, length 1.6 × width, palm obtuse, with straight, serrate margin, posterodistal corner without robust setae; dactylus reaching corner of palm, posterior margin smooth. Pereopod 3 coxa large; merus weakly expanded anteriorly; merus and carpus posterior margin lined with slender setae; propodus with 3 long slender setae and 2 distal locking setae along posterior margin; dactylus recurved. Pereopod 4 coxa deeper than wide, with large posteroventral lobe, anterior margin rounded, posterior margin sloping anteriorly; merus weakly expanded anteriorly; merus and carpus posterior margin lined with slender setae; propodus with 1 slender seta and 1 distal locking seta along posterior margin; dactylus recurved. Pereopod 5 coxa equilobate; basis expanded with posterior margin minutely crenate; merus distally expanded, margin sloping proximally, straight distally; propodus with 2 distal locking setae along anterior margin; dactylus recurved. Pereopod 6 coxa small, not lobate posteriorly; basis expanded posteriorly with minutely crenate posterior margin, without anteroventral lobe; merus expanded posteriorly margin sloping proximally, straight distally; propodus with 3 small robust setae and 2 distal locking setae along anterior margin; dactylus recurved. Pereopod 7 basis expanded posteriorly, posterior margin slightly rounded, minutely crenate, posteroventral corner rounded, posteroventral margin rounded; merus not expanded posteriorly; propodus with 3 small robust setae and 2 distal locking setae along anterior margin; dactylus recurved.

Pleon. Pleonites 1–3 dorsally smooth. Epimeron 1 posteroventral corner broadly rounded. Epimeron 2 posteroventral corner subquadrate. Epimeron 3 subquadrate, posteroventral corner rounded. Urosomites 1–3 dorsally smooth. Uropod 1 without long fine setae; peduncle with 2 dorsolateral and 2 apicomedial robust setae; outer ramus subequal to inner ramus length; outer ramus with 1 lateral robust seta; inner ramus without robust setae. Uropod 2 without fine setae; peduncle without dorsolateral setae, with 2 apicomedial robust setae; rami subequal in length, outer ramus without dorsal robust setae; inner ramus without robust setae, without constriction. Uropod 3 peduncle long, length 2 × width, without dorsolateral flange or robust setae; rami lanceolate, inner ramus reduced, 0.6 × outer ramus; outer ramus 2-articulate, article 2 short, 2.1 × width; rami without robust setae. Telson length 1.1 × width, weak emarginated notch, without dorsal robust setae, with 2 marginal penicillate seta.

Remarks. Riwo zeidleri sp. nov., the second species in the genus, can be separated from Riwo mizeui Lowry & Stoddart, 1995 from Papua New Guinea, by the antenna 1 accessory flagellum with 5 articles (4-articulate in R. mizeui ), maxilla 1 palp article two with 7 connate robust setae (only 3 in R. mizeui ) and by the weakly emarginated telson (notched in R. mizeui ).

Distribution. Marum Island, Sir Joseph Banks Group, South Australia (current study).

Figures

FIGURE 1. Riwo zeidleri sp. nov., holotype female, 4.1 mm, SAMA C 8391, Marum Island, Sir Joseph Banks Group, South Australia. Scale 0.1 mm.

FIGURE 2. Riwo zeidleri sp. nov., holotype female, 4.1 mm, SAMA C 8391, Marum Island, Sir Joseph Banks Group, South Australia. Scale 0.2 mm.