Gnathia marionis, N, Jörundur Svava R S S O & Bruce, Niel L., 2012

N, Jörundur Svava R S S O & Bruce, Niel L., 2012, New and little-known gnathiid isopod crustaceans (Cymothoida) from the northern Great Barrier Reef and the Coral Sea, Zootaxa 3380, pp. 1-33 : 16-21

Gnathia marionis sp. nov.

( Figs 10–13 )

Material examined. Holotype. 3, 2.8 mm, Marion Reefs, off Brodie Cay, 19.2833°S, 152.21667°E, 13 May 1979, lagoon pinnacle, 10 m, coll. N. L. Bruce (MTQ W30561).

Paratypes. 2 3, 3.0 mm, 2.5 mm, same location as of holotype (MTQ W30562, W30563). Male dissected, micoslides (MTQ W10733).

Description. Body 2.8 times as long as greatest width, widest at pereonite 3 and pereonite 5; dorsal surfaces smooth, sparsely setose. Cephalosome quadrate, 0.9 as long as wide, lateral margins sub-parallel; dorsal surface with sparse granules; dorsal sulcus narrow, shallow, short; translucent region present; elliptical; paraocular ornamentation strongly developed, posteromedian tubercle present. Frontolateral processes present. Frontal margin produced, truncate, median point with process. External scissura present, narrow, shallow. Mediofrontal process present on wide, even frontal margin; small, pointed, without ventral notch, with fine setae. Supraocular lobe not pronounced, long; accessory supraocular lobe not pronounced. Superior frontolateral process present, single, strong, conical, without long simple setae. Inferior frontolateral process absent. Mesioventral margin straight. Eyes present, elongate, 0.3 as long as cephalosome length, contiguous with head surface, ommatidia arranged in rows, eye colour yellow (probably faded).

Pereon lateral margins subparallel, with few setae; anteriorly smooth. Pereonite 1 not fused dorsally with cephalosome; dorsolateral margins fully obscured by cephalosome; pereonite 2 wider than pereonite 1; areae laterales present on pereonite 5; pereonite 6 without lobi laterales; lobuii weak, globular. Pleotelson 0.9 times as long as anterior width, lateral margins smooth, anterolateral margins weakly concave, posterolateral margin distally concave; mid-dorsal surface with 2 sub-median setae (short), anterolateral margin with 1 submarginal seta (short), posterolateral margin with 1 submarginal seta (prominent), apex with 2 setae.

Antennule peduncle article 2 0.7 times as long as article 1, article 3 2.3 times as long as article 2, 5.1 times as long as wide; flagellum 1 as long as article 3, with 5 articles. Antenna peduncle article 4 3 times as long as wide, 2.2 times as long as article 3, with 2 penicillate setae, and 12 simple setae (marginal and submarginal); article 5 1.1 times as long as article 4, 3.6 times as long as wide, inferior margin with 4 penicillate setae, and 16 simple setae (marginal and submarginal); flagellum 1.4 as long as article 5, with 7 articles.

Mandibl e 0.6 as long as width of cephalosome, mandible triangular, weakly curved, distally; mandible apex 20% total length; mandibular seta present. Carina present, finely dentate, along entire length. Incisor knob-like and elevated, standing clear of surface, distal denticulation absent. Blade present, dentate, strongly convex, midventrally convex, along proximal 50% of margin. Pseudoblade absent; internal lobe present, quadrate, large, smooth; dorsal lobe absent; basal neck short; erisma present; lamina dentata absent.

Maxilliped 5-articled. Maxilliped article 1 lateral margin with continuous marginal scale-setae; article 2 lateral margin with 3 plumose setae; article 3 lateral margin with 6 plumose setae; article 4 lateral margin with 5 plumose setae; article 5 with 7 plumose setae; endite extending to distal margin of article 2; without coupling setae. Pylopod article 1 1.8 as long as wide, with distolateral lobe; posterior and lateral margins forming rounded curve; lateral margin with 30 large PMS; mesial margin with continuous scale-setae, distal margin with 7 long simple setae; article 2 1.1 as long as wide; article 3 minute, with 7 setae.

Pereopods 2–6 without long plumose setae; propodus distal RS as long as proximal RS; lateral and inferior margins with prominent tubercles, pereopod 2 with tubercles on merus and carpus and basis. Pereopod 2 basis 2.3 times as long as greatest width, superior margin 5 long setae (and 2 penicillate setae), inferior margin 6 setae (long); ischium 0.6 times as long as basis, 2.1 as long as wide, superior margin with 5 setae, inferior margin with 7 setae; merus 0.5 as long as ischium, 1.4 as long as wide, superior margin with 4 long setae, inferior margin with 7 long setae; carpus 0.6 as long as ischium, 1.9 as long as wide, superior margin with 1 long setae, inferior margin with 5 setae (4 simple, 1 biserrate RS); propodus 0.9 times as long as ischium, 4.1 times as long as wide, superior margin 4 long setae (1 penicillate), inferior margin with 6 short setae, without long simple setae, and 2 RS; dactylus 0.5 as long as propodus. Pereopods 3 and 4 similar to pereopod 2. Pereopod 5 similar to pereopod 6. Basis 2.8 times as long as greatest width, superior margin with 2 long setae, and 1 penicillate seta, inferior margin with 5 long setae; ischium 0.8 as long as basis, 2.6 as long as greatest width, superior margin with 7 long setae, inferior margin with 6 long setae; merus 0.5 as long as ischium, 1.7 times as long as wide, superior margin with 4 long setae (1 biserrate), inferior margin 6 long setae, with dense patch of scale-setae; carpus 0.5 as long as ischium, 2.6 times as long as wide, superior margin with 2 long setae (1 penicillate), inferior margin with 5 long setae; propodus 0.7 as long as ischium, 4.2 times as long as wide, superior margin with 4 long setae, inferior margin with 8 long setae, and 2 RS; dactylus 0.6 as long as propodus. Penes medially united and flat lobes, penial.

Pleopod 2 exopod 1.9 as long as wide, 9 PMS; endopod 2.1 as long as wide, endopod with 8 PMS. Pleopod 2 appendix masculina absent.

Uropod rami extending beyond pleotelson, apices broadly rounded. Peduncle with 2 dorsal setae. Endopod 2.3 as long as greatest width, dorsally with 4 sensory setae; lateral margin proximally convex and distally concave, lateral margin with 4 simple setae; mesial margin weakly convex, with 6 long plumose setae. Exopod not extending to end of endopod, 3.8 times as long as greatest width; lateral margin weakly convex, with 8 simple setae; proximomesial margin straight, distally convex, mesiodistal margin with 4 long PMS.

Remarks. Gnathia marionis sp. nov. shows some resemblance to G. c o r n u t a Holdich and Harrison, 1980 in the shape of the mandible (long blade), but is distinguished from the latter and all other Australian gnathiids in having a small mediofrontal process on a wide, even frontal margin.

Etymology. The epithet is taken from the type locality.

Distribution. Marion Reef, Australian Coral Sea Territory.

Figures

FIGURE 10. Gnathia marionis sp. nov., A – B, 3, holotype, 2.8 mm (MTQ W 30561), C – F, 3 paratype, 3.0 mm (MTQ W 10733). A, habitus. B, pleonites and pleotelson. C, cephalosome, dorsal view. D, cephalosome, dorso-lateral view. E, cephalosome, lateral view. F, cephalosome, ventral view. Scale = 0.5 mm.

FIGURE 11. Gnathia marionis sp. nov., 3, paratype, 3.0 mm (MTQ W 10733). A, antennule. B, antenna. C, maxilliped. D, pylopod. E, second and third article of pylopod. F, outline of second and third article of pylopod.

FIGURE 12. Gnathia marionis sp. nov., 3, paratype, 3.0 mm (MTQ W 10733). A, pereopod 2. B, propodus and dactylus of pereopod 2. C, pereopod 6.

FIGURE 13. Gnathia marionis sp. nov., 3, paratype, 3.0 mm (MTQ W 10733). A, pleopod 2. B, pleotelson and outline of uropod. C, uropod.