Gnathia carinodenta, Svavarsson & Bruce, 2019

Svavarsson, Jörundur & Bruce, Niel L., 2019, New gnathiid isopod crustaceans (Cymothoida) from Heron Island and Wistari Reef, southern Great Barrier Reef, Zootaxa 4609 (1), pp. 31-67 : 48-52

Gnathia carinodenta sp. nov.

( Figs 14–17 )

Material examined. Holotype. ♂ (3.3 mm), Heron Island , 21.4449°S, 151.9107°E, outer reef flat, 1979, in dead coral, coll. N.L. Bruce (MTQ W10683).

Paratypes. ♂ (2.7 mm; dissected + 3 microslides), Heron Island , 23°45195’S, 151°86712’E, 11 November 2009, CReefs stn HI09-002 ( MTQ W31661) . ♂ (2.8 mm), Heron Island , Heron–Wistari channel, 23°27.248’S, 151°55.005’E, 25 November 2009, coral rubble, 29–30 m, CReefs stn HI09-106D, coll. K. Schnabel and S. Smith ( MTQ W34091) .

Description. Body ( Fig. 14A ) 2.6 times as long as greatest width, widest at pereonite 3; dorsal surfaces coarsely pitted, sparsely setose. Cephalosome ( Fig. 14 B–D) quadrate, 0.7 times as long as wide, lateral margins narrowing posteriorly; dorsal surface with numerous granules; dorsal sulcus wide, deep, extended; translucent region present; elliptical; paraocular ornamentation absent, posteromedian tubercle present. Frontolateral processes present. Frontal margin straight. External scissura present, wide, deep. Mediofrontal process present, weak, rounded, without ventral notch, without fine setae. Supraocular lobe pronounced, wide; accessory supraocular lobe not pronounced. Superior frontolateral process present, single, strong, conical, with few simple setae. Inferior frontolateral process present, acute, conical, without setae. Mesioventral margin straight. Eyes present, round, 0.3 times as long as cephalosome length, contiguous with head surface, ommatidia arranged in rows, eye colour yellow.

Pereon ( Fig. 14A ) lateral margins subparallel, with few setae; anteriorly with sparse 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 weak, globular.

Antennula ( Fig. 15A ) peduncle article 2 0.8 times as long as article 1, article 3 2.0 times as long as article 2, 3.5 times as long as wide; flagellum 1.2 times as long as article 3, with 5 articles. Antenna ( Fig. 15B ) peduncle article 4 2.4 times as long as wide, 2.2 times as long as article 3, with 2 penicillate setae, and 4 simple setae; article 5 1.2 times as long as article 4, 2.9 times as long as wide, inferior margin with 3 penicillate setae, with 14 simple setae; flagellum 1.3 times as long as article 5, with 7 articles.

Mandibl e ( Fig. 14 B–D) 0.6 times as long as width of cephalosome, mandible rectangular, weakly curved distally; mandible apex 24 % total length; mandibular seta present. Carina present, strongly dentate along distal half. Blade present, dentate, strongly convex, midventrally convex, dentate along 50 % of inferior margin. Pseudoblade absent; internal lobe present, rounded, small, smooth; dorsal lobe absent; basal neck short; erisma present; lamina dentata not visible in dorsal view.

Maxilliped ( Fig. 15C ) 5-articled. Maxilliped article 1 lateral margin with continuous marginal scale-setae; ar- ticle 2 lateral margin with 3 plumose setae; article 3 lateral margin with 8 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 ( Fig. 15D ) article 1 1.7 times as long as wide, without distolateral lobe; posterior and lateral margins forming rounded curve; lateral margin with 30 large PMS; mesial margin with continuous scale-setae, distal margin with 2 simple setae; article 2 ( Fig. 15E ) 0.8 times as long as wide; article 3 ( Fig. 15E ) minute, with 2 setae.

Pereopods 2–6 without long plumose setae; propodus distal RS slightly longer than proximal RS; lateral and inferior margins with weak tubercles, pereopod 2 with tubercles on basis to carpus. Pereopod 2 ( Fig. 16A ) basis 2 times as long as greatest width, superior margin with 7 setae (three penicillate), inferior margin with 4 setae; ischium 0.81 times as long as basis, 2.2 times as long as wide, superior margin with 5 setae, inferior margin with 5 setae; merus 0.5 times as long as ischium, 1.4 times as long as wide, superior margin with 2 setae, inferior margin with 7 setae; carpus 0.5 times as long as ischium, 2.1 times as long as wide, superior margin with 1 seta, inferior margin with 4 setae (one biserrate); propodus ( Fig. 16B ) 0.7 times as long as ischium, 3.4 times as long as wide, superior margin with 5 setae (one penicillate), inferior margin with 0 short setae, 3 simple setae; dactylus ( Fig. 16B ) 0.5 times as long as propodus. Pereopods 3 and 4 similar to pereopod 2. Pereopod 5 similar to pereopod 6. Pereopod 6 ( Fig. 16C ) with tubercles on basis to carpus, basis 2.7 times as long as greatest width, superior margin with 3 setae, and 4 penicillate setae, inferior margin with 6 setae; ischium 0.7 times as long as basis, 2.3 times as long as greatest width, superior margin with 3 setae, inferior margin with 5 setae and dense patch of scale-setae; merus 0.5 times as long as ischium, 1.7 times as long as wide, superior margin with 4 setae (2 biserrate), inferior margin with 4 setae, with dense patch of scale-setae; carpus 0.5 times as long as ischium, 2.2 times as long as wide, superior margin with 2 setae (one penicillate), inferior margin with 3 setae (one biserrate); with dense patch of scale-setae; propodus ( Fig. 16D ) 0.8 times as long as ischium, 4.2 times as long as wide, superior margin with 4 setae (one penicillate), inferior margin with 4 setae, and 2 RS; dactylus ( Fig. 16D ) 0.5 times as long as propodus. Penes low tubercles.

Pleotelson ( Fig. 17D ) 1.0 times as long as anterior width, lateral margins sparsely serrate, anterolateral margins weakly concave, posterolateral margin distally weakly concave; mid-dorsal surface with 2 sub-median setae, anterolateral margin with 2 submarginal setae, posterolateral margin with 2 submarginal setae, apex with 2 setae.

Pleopod 1 ( Fig. 17A ) exopod 2 times as long as wide, distally broadly rounded, with ~ 8 PMS; endopod 2.1 times as long as wide, distally broadly rounded, with 7 PMS; peduncle 1.2 times as wide as long, mesial margin with 2 coupling setae. Pleopod 2 ( Fig. 17B ) endopod 1.9 times as long as wide, with 7 PMS. Pleopod 2 appendix masculina present, with parallel margins, 0.5 times as long as endopod, distally bluntly rounded.

Uropod ( Fig. 17C, D ) rami extending beyond pleotelson, apices broadly rounded. Peduncle with 1 dorsal seta. Endopod 2.1 times as long as greatest width, dorsally with 7 sensory setae; lateral margin weakly convex, lateral margin with 3 simple setae; mesial margin strongly convex, with 6 long plumose setae. Exopod not extending to end of endopod, 3.5 times as long as greatest width; lateral margin weakly sinuate, with 7 simple setae; proximomesial margin straight, distally convex, mesiodistal margin with 4 long PMS.

Remarks. Of the known Gnathia species, G. carinodenta sp. nov. shows some resemblance in the shape of the frontolateral process to Gnathia calmani Monod, 1926 ( Monod 1926) . Gnathia carinodenta sp. nov. is, however, distinguish from this species and all other Australian gnathiids by the shape of the carina and the denticulations on the carina .

There is a minor variation in the number (two or three) of teeth in the denticulation on the carina , both within specimens and between them. The largest specimen (3.3 mm, holotype) has somewhat longer mandible than the smaller specimens and the inferior mediofrontal processes are more rounded in the smaller specimens. We consider this to be a variation rather than this representing two species. The eyes are yellow, but prolonged preservation time may have influenced the colour.

Etymology. The epithet refers to the denticulations on the carina .

Distribution. Heron Island, southern Great Barrier Reef Queensland; intertidal to 30 m.

Figures

FIGURE 14. Gnathia carinodenta sp. nov., A–B, ♂, holotype, 3.3 mm (MTQ W10683); C–D, ♂, paratype, 2.7 mm (MTQ W31661). A, habitus. B, cephalosome, dorsal view. C, cephalosome, ventral view. D, cephalosome, lateral view. Scale for A = 1.0 mm.

FIGURE 15. Gnathia carinodenta sp. nov., ♂, paratype, 2.7 mm (MTQ W31661). A, antennula. B, antenna. C, maxilliped. D, pylopod. E, second and third article of pylopod.

FIGURE 16. Gnathia carinodenta sp. nov., ♂, paratype, 2.7 mm (MTQ W31661).A, pereopod 2. B, propodus and dactylus of pereopod 2. C, pereopod 6. D, propodus and dactylus of pereopod 6.

FIGURE 17. Gnathia carinodenta sp. nov., ♂, paratype, 2.7 mm (MTQ W31661). A, pleopod 1. B, pleopod 2, endopod and appendix masculina. C, uropod. D, pleotelson and outline of uropods.