Riwo mizeui Lowry & Stoddart, 1995

Lowry, J. K. & Stoddart, H. E., 2009, Lysianassidae *, Zootaxa 2260 (1), pp. 561-597 : 568-571

Riwo mizeui Lowry & Stoddart, 1995

( Figs 5 , 6 )

Riwo mizeui Lowry & Stoddart, 1995: 127 , figs 17–19.

Material examined. Female, 3.6 mm, AM P69376; male, 2.8 mm, AM P69377; 36 unsexed, AM P69378; ( QLD 727). 1 unsexed, AM P69379 ( QLD 683).

Type locality. Wongad Natun reef, Madang Lagoon, Papua New Guinea, western South Pacific Ocean (5°08.31'S 145°49.36'E), 4 m depth .

Description. Based on female, 3.6 mm, AM P69376.

Head and body. Body without dorsal carina. Head lateral cephalic lobes subtriangular, with apically rounded margins; eyes oval. Antenna 1 subequal to antenna 2; flagellum article 1 slightly longer than article 2, with weak 1-field callynophore, robust setae absent from proximal articles; calceoli absent; accessory flagellum with 4 articles. Antenna 2 less than 40% of body length; peduncular article 3 long; calceoli absent. Mouthparts forming a subquadrate bundle. Epistome / upper lip separate, epistome less produced than upper lip, straight; upper lip produced, rounded apically. Mandible molar a small, smooth flap with finely setose margins; palp attached proximally, article 3 without A3–setae. Maxilla 1 outer plate with 10 setal-teeth in reduced 6/5 arrangement; setal-tooth 7, left and right symmetrical, cuspidate distally; palp distal margin with apical robust setae and serrations. Maxilliped inner plates poorly developed, not reaching half the length of the outer plate; outer plates without apical robust setae; palp 4–articulate, article 4 well developed.

Pereon. Gnathopod 1 simple; coxa large, about as long as coxa 2, subrectangular with straight anterior margin; basis without setae along anterior margin; ischium short; carpus short (length 1.9 x breadth), subequal in length to propodus, without posterior lobe; propodus longer than broad, margins tapering; dactylus inner margin not serrated. Gnathopod 2 chelate; carpus longer than (2.4 x) propodus; palm slightly obtuse; dactylus minute. Pereopod 4 coxa with well developed posteroventral lobe. Pereopod 5 coxa anterior lobe slightly deeper than posterior lobe; basis about as long as broad.

Pleon. Epimeron 3 posterior margin smooth, posterodistal corner narrowly rounded. Urosomite 1 without anterodorsal notch, slightly rounded dorsally, without boss. Uropod 1 rami subequal. Uropod 2 rami subequal, inner ramus without marginal constriction. Uropod 3 rami distinctly unequal, without plumose setae; outer ramus 2–articulate, article 2 short; inner ramus not reaching end of article 1 of outer ramus. Telson subequal in length and breadth, notched, without dorsal robust setae.

Male (sexually dimorphic characters) based on male, 2.8 mm, AM P69377. Antenna 1 with weak 2-field callynophore; calceoli present. Antenna 2 calceoli present.

Habitat. Scavenger living among soft and hard corals in 3 to 50 m depth.

Remarks. According to Lowry & Stoddart (1995) Riwo mizeui is a scavenger which occurs on living coral bottoms. It is the only lysianassid known from the Great Barrier Reef which has both a simple first gnathopod and distinctly unequal rami on uropod 3. Pseudambasia acuticaudata also has unequal rami on uropod 3, but the first gnathopod is weakly subchelate. Riwo mizeui differs from Shoemakerella barnardi , which also has a simple gnathopod 1, in the size of the eyes which cover most of the head (smaller in S. barnardi ), the presence of robust setae on the distal margin of maxilla 1 palp (serrate in S. barnardi ) and epimeron 3 which is narrowly rounded (broadly rounded in S. barnardi ).

Living specimens R. mizeui have a black-speckled chromatophore pattern on the body (body white in S. barnardi ).

Distribution. Australia. Queensland: Ashmore Reef (current study), inside Outer Barrier (current study). Papua New Guinea. Madang Lagoon ( Lowry & Stoddart 1995).

Figures

FIGURE 5. Riwo mizeui Lowry & Stoddart, 1995, female, 3.6 mm, AM P69376, and male, 2.8 mm, AM P69377, Ashmore Reef, Great Barrier Reef.

FIGURE 6. Riwo mizeui Lowry & Stoddart, 1995, female, 3.6 mm, AM P69376 and male, 2.8 mm, AM P69377, Ashmore Reef, Great Barrier Reef.