Riwo zeidleri Hughes & Lowry, 2015, sp. nov.

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).