Gnathia coralmaris, 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 : 8-12

Gnathia coralmaris sp. nov.

( Figs 4–7 )

Material examined. Holotype. 3, 1.9 mm, Mellish Reef, Australian Coral Sea, 17.406667°S, 155.858333°E, 1 May 1979, lagoon, 6 m, coll. N. L. Bruce (MTQ W30559).

Paratype. 3, 2.3 mm, dissected, same data as holotype (MTQ W10729, + 9 microslides).

Description. Body 2.8 times as long as greatest width, widest at pereonite 4; dorsal surfaces polished, sparsely setose. Cephalosome quadrate, 0.8 as long as wide, lateral margins convex; dorsal surface with sparse granules; dorsal sulcus wide, shallow, extended; translucent region present; elliptical; paraocular ornamentation strongly developed, posteromedian tubercle present. Frontolateral processes present. Frontal margin produced, triangular, median point excavate. External scissura present, wide, deep. Mediofrontal process present, weak, rounded, with ventral notches, without fine setae. Supraocular lobe pronounced, wide; accessory supraocular lobe not pronounced. Superior frontolateral process present, single, strong, unequally apically bifid, with 3 long simple setae. Inferior frontolateral process absent. Eyes present, elongate, 0.3 as long as cephalosome length, contiguous with head surface, ommatidia arranged in rows, eye colour yellow.

Pereon lateral margins subparallel, with few setae; anteriorly smooth and 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 absent on pereonite 5; pereonite 6 without lobi laterales; lobuii well-developed, globular. Pleotelson 0.9 times as long as anterior width, lateral margins serrate (at mid-margin), anterolateral margins concave, posterolateral margin weakly concave; mid-dorsal surface with 2 sub-median setae (small), anterolateral margin with 1 submarginal seta (small), posterolateral margin with 2 submarginal setae (prominent), apex with 2 setae.

Antennule peduncle article 3 1.9 times as long as article 2, 4.1 times as long as wide; flagellum 0.9 as long as article 3, with 5 articles. Antenna peduncle article 4 2.9 times as long as wide, 2.2 times as long as article 3, without penicillate setae, and with 4 simple setae; article 5 1.2 times as long as article 4, 3.7 times as long as wide, inferior margin with 2 penicillate setae, with 12 simple setae; flagellum 0.9 as long as article 5, with 6 articles.

Mandibl e 0.5 as long as width of cephalosome, mandible triangular, weakly curved, evenly; mandible apex 20% total length; mandibular seta present. Carina present, smooth, along entire length. Incisor dentate, distal denticulation present. Blade present, smooth, strongly convex, proximally convex, along proximal 50% of margin. Pseudoblade absent; internal lobe absent; 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 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 25 large PMS; mesial margin with continuous scale-setae, distal margin with 4 long simple setae; article 2 1.2 as long as wide; article 3 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 ischium. Pereopod 2 basis 2.2 times as long as greatest width, superior margin 6 long setae, inferior margin 4 setae; ischium 0.6 times as long as basis, 2.1 as long as wide, superior margin with 4 setae, inferior margin with 6 setae; merus 0.5 as long as ischium, 1.5 as long as wide, superior margin with 3 long setae, inferior margin with 6 long setae; carpus 0.6 as long as ischium, 1.8 as long as wide, superior margin with 1 long seta, inferior margin with 4 setae (1 biserrate); propodus 0.9 times as long as ischium, 3.2 times as long as wide, superior margin 3 long setae, inferior margin with 3 short setae, without long simple setae (1 penicillate seta), 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 basis 2.1 times as long as greatest width, superior margin with 6 long setae, and no penicillate setae, inferior margin with 5 long setae; ischium 0.8 as long as basis, 2.3 as long as greatest width, superior margin with 5 long setae, inferior margin with 5 long setae; merus 0.6 as long as ischium, 1.6 times as long as wide, superior margin with 2 long setae (and 2 biserrate setae), inferior margin 5 long setae, with dense patch of scale-setae; carpus 0.5 as long as ischium, 1.9 times as long as wide, superior margin without long setae (1 penicillate seta), inferior margin with 4 long setae; propodus 0.7 as long as ischium, 2.8 times as long as wide, superior margin with 4 long setae (and 1 penicillate seta), inferior margin with 5 long setae, and 2 RS; dactylus 0.7 as long as propodus. Penes opening flush with surface of sternite 7.

Pleopod 2 exopod 1.9 as long as wide, 9 PMS; endopod 1.9 as long as wide, endopod with 7 PMS. Pleopod 2 appendix masculina present, with parallel margins, 0.5 times as long as endopod, distally bluntly rounded.

Uropod rami extending beyond pleotelson, apices broadly rounded. Peduncle with 1 dorsal seta. Endopod 2.3 as long as greatest width, dorsally with 6 sensory setae; lateral margin distally concave, lateral margin with 3 simple setae; mesial margin strongly convex, with 7 long plumose setae. Exopod not extending to end of endopod, 3.8 times as long as greatest width; lateral margin weakly convex, with 7 simple setae; proximomesial margin straight, distally convex, mesiodistal margin with 4 long PMS.

Remarks. Gnathia coralmaris sp. nov. is distinguished from all Australian species by the shape of the frontal margin and the frontal processes. Gnathia coralmaris sp. nov. is most similar to Gnathia phallonajopsis Monod, 1925 from the Mediterranean and Gnathia perimulica Monod, 1926 from the Gulf of Thailand. Gnathia coralmaris differs from G. perimulica in having smooth frontal margin (crenulated mid-part and crenulated laterofrontal process in G. p e r i m u l i c a), and from G. phallonajopsis by lacking internal lobe (lobe present in G. phallonajopsis ) on the mandible.

Etymology. The epithet combines the Latin words corallium and maris.

Distribution. Mellish Reef, Australian Coral Sea Territory.

Figures

FIGURE 4. Gnathia coralmaris sp. nov. A, habitus, 3, holotype, 1.9 mm (MTQ W 30559), B – D, 3 paratype, 2.3 mm (MTQ W 10729). B, cephalosome, dorsal view. C, cephalosome, dorso-lateral view. D, cephalosome, lateral view. Scale = 0.5 mm.

FIGURE 5. Gnathia coralmaris sp. nov., 3, paratype, 2.3 mm (MTQ W 10729). A, antennule. B, antenna. C, maxilliped. D, pylopod. E, second and third article of pylopod.

FIGURE 6. Gnathia coralmaris sp. nov., 3, paratype, 2.3 mm (MTQ W 10729). A, pereopod 2. B, propodus and dactylus of pereopod 2. C, pereopod 6. D, propodus and dactylus of pereopod 6.

FIGURE 7. Gnathia coralmaris sp. nov., 3, paratype, 2.3 mm (MTQ W 10729). A, pleopod 2. B, pleotelson and outline of uropod. C, uropod.