Quadrisegmentum triangulum Hirayama, 1988

Guerra-García, José M. & Lowry, J. K., 2009, Caprellidae *, Zootaxa 2260 (1), pp. 290-327 : 323-325

Quadrisegmentum triangulum Hirayama, 1988

( Fig. 17 )

Quadrisegmentum triangulum Hirayama, 1988: 1089 , figs 1–3. —Guerra-García, 2006: 440, fig. 39.

Material examined. 1 male, ~ 7.7 mm, 1 female, ~ 5.5 mm, AM P61725 ( QLD 1565 ). See station list for occurrences ( Lowry & Myers 2009) and Guerra-García (2006) for complete material examined .

Type locality. West Islet , Ashmore Islands, north-west Western Australia (12º41.28'S 122º59.14'E), on gorgonian host, Isis hippurus Linnaeus , 18 m depth .

Description. Based on 1 male, ~ 7.7 mm, 1 female, ~ 5.5 mm, AM P61725

Head and pereonites slender. Head/pereonite 1 fused (suture absent), slightly concave along dorsal margin; eye large, distinctive, or large, protruding. Antenna 1 well developed; slender, about 0.5 x body length; peduncle article 2 longest, article 3 straight; accessory flagellum absent; flagellum 0.4 x peduncular length or 0.5 x peduncular length, with more than 2 articles. Antenna 2 0.75 x antenna 1 length, slender; peduncle without setae; with more than 4 articles (5–7 articles). Labrum notched, forming rounded quadrilateral projections. Mandible right incisor with 5 teeth, right lacinia mobilis transformed into a plate, accessory setal row with 7 setae; molar absent; left incisor with 4 teeth, lacinia mobilis transformed into a serrated plate, with 3 trapezoid plates decreasing in size; palp 3–articulate, palp setal formula 1-0-1. Maxilla 1 outer plate with 6 stout apical setal-teeth. Maxilliped inner plate smaller than outer plate; serrate distally; outer plate subequal to inner plate; palp article 2 scarcely setose on inner margin; palp article 4 not enlarged, not falcate.

Pereon. Pereonites 2 to 7 not fused; pereonite 5 longest. Pereonite 1 without projections. Gnathopod 1 distinctly smaller than gnathopod 2; propodus triangular, palm begins 2/5 along posterior margin, smooth, without large, rounded knob proximally; dactylus curved, inner margin smooth. Pereonite 2 without projections. Gnathopod 2 situated near middle of pereonite 2; basis about 1.5 x length of pereonite 2, without anterodistal projection; ischium without anterodistal projection; propodus elongate, massive, anterodistal margin straight, without anterodistal triangular projection, without projections along mid-anterior margin; palm without proximal cavity filled with membranous sack, palm proximal projection with 2 robust (grasping) setae, palm margin concave, smooth, without hook-like projection at base of dactylus, with broad well developed distal shelf, without projection, without sinus, without midpalmar projection. Pereonite 3 without projections. Pereopod 3 well developed, with 6 articles. Pereonite 4 without projections. Pereopod 4 well developed, with 6 articles. Pereopod 5 reduced or vestigial, with 4 slender articles. Pereopod 6 basis longest followed by merus. Pereopod 7 similar to pereopod 6.

Gills on pereonites 2 to 4. Pereonite 2 gill rounded. Pereonite 3 gill length about 2/3 of corresponding pereonite, straight, elongate, cylindrical. Pereonite 4 gill length about 2/3 of corresponding pereonite, straight, elongate, cylindrical.

Pleon. Uropod 1 present. Uropod 2 ramus well developed.

Female (sexually dimorphic characters). Gnathopod 2 situated near anterior end of pereonite 2; basis (proximal-most article) subequal in length to pereonite 2; large; palm margin convex or straight.

Habitat. Patch reefs, algae and coral rubble, associated with the hydroid Halopteris buskii and the sponge Clathria reinwardti , 2– 30 m.

Remarks. Quadrisegmentum triangulum is one of the most abundant caprellid species on the Great Barrier Reef.

Distribution. Australia: Queensland: off Coconut Beach; off Crystal Beach; Mangrove Beach, Blue lagoon; between Bird Islet and South Island; Chinamans Ridge, Watsons Bay; Mermaid Cove; Pidgin Point; North Point; south of "Washing Machine", north-east side of Lizard Island (Guerra-García 2006). Lord Howe Island. Middleton Reef (Guerra-García 2006). Western Australia: Ashmore Islands ( Hirayama 1988).

Papua New Guinea: Motupore Island and Madang ( Guerra-García 2003a).

Figures

FIGURE 17. Quadrisegmentum triangulum Hirayama, 1988. A, Male, ~7.7 mm, B, female, ~5.5 mm, AM P61725, north-east side of Lizard Island, Great Barrier Reef. Refigured from Guerra-García (2006).