Gnathia varanus, 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 : 21-26

Gnathia varanus sp. nov.

( Figs 14–17 )

Material examined. Holotype. 3, 4.0 mm, Lizard Island, North Queensland, lagoon entrance in from Seabird Islet, 14.68900°S, 145.46710°E, patch reef, 19 April 2008, small rubble, dead coral, 15 m, CReefs stn CGLI 041E, coll. N.L. Bruce & M. Błażewicz-Paszkowycz (MTQ W14160).

Paratypes. 6 3 (dissected paratype, MTQ W14161; 2 3 IMNH 2724; 3 3 MTQ W14162, same locality as holotype).

Description. Body 3.1 times as long as greatest width, widest at pereonite 2 and pereonite 3; dorsal surfaces sparsely punctate, sparsely setose. Cephalosome quadrate, 0.8 as long as wide, lateral margins narrowing posteriorly; dorsal surface with numerous granules; dorsal sulcus wide, shallow, extended; translucent region absent; paraocular ornamentation strongly developed, posteromedian tubercle present. Frontolateral processes present. Frontal margin straight, median point with process. External scissura present, wide, shallow. Mediofrontal process present, strong, acute, without ventral notch, without fine setae. Supraocular lobe pronounced, wide; accessory supraocular lobe not pronounced. Superior frontolateral process present, paired, strong, conical, with 2 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 faded, not known. Pereon lateral margins narrowing posteriorly, with few setae; anteriorly with numerous fine granules. 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 well-developed, globular. Pleotelson 1.3 times as long as anterior width, lateral margins finely serrate, anterolateral margins distally weakly concave, posterolateral margin straight; mid-dorsal surface with 2 sub-median setae, anterolateral margin with 1 submarginal seta, posterolateral margin with 1 submarginal seta, apex with 2 setae.

Antennule peduncle article 2 1.0 times as long as article 1, article 3 1.8 times as long as article 2, 4.7 times as long as wide; flagellum 1.3 as long as article 3, with 5 articles. Antenna peduncle article 4 2.6 times as long as wide, 1.9 times as long as article 3, with 1 penicillate seta, and 13 simple setae (marginal and submarginal); article 5 1.2 times as long as article 4, 3.6 times as long as wide, inferior margin with 1 penicillate seta, with 35 simple setae (dense setal field on dorsal and ventral surfaces); flagellum 1.6 as long as article 5, with 7 articles.

Mandibl e 0.6 as long as width of cephalosome, mandible triangular, strongly curved, distally; mandible apex 30% total length; mandibular seta present. Carina present, smooth, along entire length. Incisor elevated, standing clear of surface, distal denticulation absent. Blade present, dentate, strongly convex, proximally convex, along proximal 50% of margin. Pseudoblade absent; internal lobe present, quadrate, small, 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 4 plumose setae; article 3 lateral margin with 7 plumose setae; article 4 lateral margin with 5 plumose setae; article 5 with 8 plumose setae; endite extending to distal margin of article 2; without coupling setae. Pylopod article 1 1.8 as long as wide, without distolateral lobe; posterior and lateral margins forming rounded curve; lateral margin with 34 large PMS; mesial margin with continuous scale-setae, distal margin with 12 long simple setae; article 2 1.64 as long as wide; article 3 minute.

Pereopods 2–6 without long plumose setae; propodus distal RS as long as proximal RS; lateral and inferior margins with weak tubercles, pereopod 2 with tubercles on basis. Pereopod 2 basis 2.3 times as long as greatest width, superior margin 5 long setae (and 1 penicillate seta), inferior margin 7 setae; ischium 0.8 times as long as basis, 2.5 as long as wide, superior margin with 10 setae, inferior margin with 9 setae; merus 0.5 as long as ischium, 1.5 as long as wide, superior margin with 4 long setae, inferior margin with 8 long setae; carpus 0.6 as long as ischium, 2.1 as long as wide, superior margin with 2 long setae, inferior margin with 6 setae (1 biserrate); propodus 0.8 times as long as ischium, 3.9 times as long as wide, superior margin 6 long setae, inferior margin with 6 short setae (1 penicillate seta), 6 long simple setae, and 2 RS; dactylus 0.6 as long as propodus. Pereopods 3 and 4 similar to pereopod 2. Pereopod 5 similar to pereopod 6. Pereopod 6 with tubercles on merus and carpus and with tubercles on superior margin of basis, basis 2.2 times as long as greatest width, superior margin with 9 long setae, and 1 penicillate seta, inferior margin with 7 long setae; ischium 0.8 as long as basis, 2.4 as long as greatest width, superior margin with 9 long setae, inferior margin with 9 long setae; merus 0.6 as long as ischium, 1.4 times as long as wide, superior margin with 3 long setae, inferior margin 9 long setae, without dense patch of scale-setae; carpus 0.6 as long as ischium, 2.5 times as long as wide, superior margin with 3 long setae, inferior margin with 6 long setae; propodus 0.7 as long as ischium, 3.7 times as long as wide, superior margin with 5 long setae, inferior margin with 6 long setae, and 2 RS; dactylus 0.6 as long as propodus. Penes opening flush with surface of sternite 7.

Pleopod 2 exopod 1.5 as long as wide, 9 PMS; endopod 1.7 as long as wide, endopod with 8 PMS. Pleopod 2 appendix masculina absent.

Uropod rami extending beyond pleotelson, apices narrowly rounded. Peduncle with 2 dorsal setae. Endopod 2.8 as long as greatest width, dorsally with 3 sensory setae; lateral margin proximally convex, lateral margin with 4 simple setae; mesial margin weakly convex, with 6 long plumose setae. Exopod not extending to end of endopod, 4.1 times as long as greatest width; lateral margin weakly convex, with 13 simple setae; proximomesial margin straight, mesiodistal margin with 4 long PMS.

Remarks. Gnathia varanus sp. nov. is distinguished from all other Australian gnathiids by the large mediofrontal and paired superior frontolateral processes, the latter being located close to the mesial line of the cephalosome. Several gnathiid species have strong superior frontolateral processes close to the medial line (e.g. Gnathia venusta Monod, 1925 ; Gnathia illepida Monod, 1923 ), but these species have different configuration of the frontolateral processes.

Etymology. The species name is the generic name for the large Sand Goanna, Varanus gouldii (Gray, 1838), for which the island was given its English name (noun in apposition).

Distribution. Known only from Lizard Island, northern Great Barrier Reef.

Figures

FIGURE 14. Gnathia varanus sp. nov. A, habitus, 3, holotype, 4.0 mm (MTQ W 14160), B – E, 3 paratype, 3.8 mm (MTQ W 14161). B, cephalosome, dorsal view. C, cephalosome, dorso-lateral view. D, cephalosome, lateral view. E, cephalosome, ventral view. Scale = 1.0 mm.

FIGURE 15. Gnathia varanus sp. nov., 3, paratype, 3.8 mm (MTQ W 14161). A, antennule. B, antenna. C, maxilliped. D, pylopod. E, second and third article of pylopod and outline of the same articles.

FIGURE 16. Gnathia varanus sp. nov., 3, paratype, 3.8 mm (MTQ W 14161). A, pereopod 2. B, propodus and dactylus of pereopod 2. C, pereopod 6.

FIGURE 17. Gnathia varanus sp. nov., 3, paratype, 3.8 mm (MTQ W 14161). A, pleopod 2. B, pleotelson and uropods.