Gnathia hamletgast, 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 : 13-16

Gnathia hamletgast sp. nov.

( Figs 8–9 )

Material examined. Holotype. 3, 2.6 mm, Bennett Island, Chesterfield reefs, northern reef, 8 May 1979, coral rock, lagoon, coll. N. L. Bruce (MTQ W10740).

Description. Body 3.2 times as long as greatest width, widest at pereonite 3; dorsal surfaces polished, sparsely setose. Cephalosome quadrate, 0.8 as long as wide, lateral margins convex; dorsal surface with sparse granules; dorsal sulcus narrow, shallow, extended; translucent region absent; paraocular ornamentation strongly developed, posteromedian tubercle present. Frontolateral processes present. Frontal margin convex, median point with process. External scissura present, narrow, deep. Mediofrontal process present, strong, spatuloid, bifid, without ventral notch, without fine setae. Supraocular lobe pronounced, wide; accessory supraocular lobe not pronounced. Superior frontolateral process present, strong, unequally apically bifid, with 2 long simple setae. Inferior frontolateral process present, apically unequally bifid, without setae. Mesioventral margin straight. Eyes present, elongate, 0.3 as long as cephalosome length, contiguous with head surface, ommatidia arranged in rows, eye colour dark brown. 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 absent on pereonite 5; pereonite 6 without lobi laterales; lobuii well-developed, globular.

Mandibl e 0.6 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 knob-like, distal denticulation absent. Blade present, dentate, with distinct angle, convex, along proximal 50% of margin. Pseudoblade absent; internal lobe present, rounded, large, smooth; dorsal lobe absent; basal neck short; erisma absent; lamina dentata absent.

Pereopods 2–6 without long plumose setae; propodus distal RS 1.5 length of proximal RS; lateral and inferior margins with weak tubercles, pereopod 2 with tubercles on merus and carpus and basis. Pereopod 2 basis 2.3 times as long as greatest width, superior margin 12 long setae, inferior margin 7 setae; ischium 0.8 times as long as basis, 2.4 as long as wide, superior margin with 7 setae, inferior margin with 9 setae; merus 0.4 as long as ischium, 1.2 as long as wide, superior margin with 4 long setae, inferior margin with 7 long setae; carpus 0.5 as long as ischium, 1.9 as long as wide, superior margin with 2 long setae, inferior margin with 7 setae (1 biserrate); propodus 0.8 times as long as ischium, 2.8 times as long as wide, superior margin 4 long setae (1 penicillate), inferior margin with 6 short setae, 1 long simple 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 with tubercles on carpus, basis 2.6 times as long as greatest width, superior margin with 11 long setae, and 1 penicillate seta, inferior margin with 3 long setae; ischium 0.8 as long as basis, 2.6 as long as greatest width, superior margin with 9 long setae (5 short, 3 long and 1 short acute RS), inferior margin with 9 long setae (4 short submarginal, 5 long marginal); merus 0.5 as long as ischium, 1.5 times as long as wide, superior margin with 5 long setae, inferior margin 6 long setae, with dense patch of scale-setae; carpus 0.5 as long as ischium, 2.3 times as long as wide, superior margin with 2 long setae (and 1 penicillate seta), inferior margin with 4 long setae; propodus 0.8 as long as ischium, 3.8 times as long as wide, superior margin with 6 long setae (and 1 penicillate seta), inferior margin with 7 long setae, and 2 RS; dactylus 0.5 as long as propodus. Penes medially united, penial process 7.4 times as long as basal width.

Remarks. The somewhat long, spatuloid mediofrontal process readily distinguishes Gnathia hamletgast sp. nov. from all Australian gnathiids. Gnathia calamitosa Monod, 1926 from southeastern Australia shows some resemblance, but mediofrontal process of that species is not strongly bifid. Furthermore the superior frontolateral process is unequally apically bifid in G. hamletgast , while being simple and rounded in G. calamitosa . The species shows also some resemblance to G. regalis Monod, 1926 from New Zealand in the shape of the mediofrontal process. The mandibles, however, differ in the absence of a medial lobe in G. re g a l i s, but being present in Gnathia hamletgast .

An abbreviated description is given here as dissection was minimal in order to preserve the integrity of the holotype.

Etymology. Bennett Island is named after Captain J.B. Bennett of the schooner Prince of Denmark, a whaler wrecked on the Chesterfield Reefs on 19 March 1863. The crew used the remains of the whaler to build a new boat, the Hamlet´s Ghost, to successfully escape and rescue from the island; noun in apposition.

Distribution. Bennett Island, Chesterfield reefs, Coral Sea.

Figures

FIGURE 8. Gnathia hamletgast sp. nov. 3, holotype, 2.6 mm (MTQ W 10740). A, habitus, B, cephalosome, dorsal view. C, anterior end of cephalosome, dorso-lateral view. D, cephalosome, lateral view. E, anterior end of cephalosome, ventral view. Scale = 1.0 mm.

FIGURE 9. Gnathia hamletgast sp. nov., 3, holotype, 2.6 mm (MTQ W 10740). A, pereopod 2. B, pereopod 6. C, propodus and dactylus of pereopod 6. D, penis.