Garthambrus tani, Ahyong, 2008

Ahyong, Shane T., 2008, Deepwater crabs from seamounts and chemosynthetic habitats off eastern New Zealand (Crustacea: Decapoda: Brachyura), Zootaxa 1708 (1), pp. 1-72 : 55-59

Garthambrus tani sp. nov.

( Figs 25–27 )

Tutankhamen sp. — Clark & O’Shea 2001: 15. — Martin & Haney 2005: 451, 497.

Type material. HOLOTYPE: NIWA 6776 , 1 male (cl 13.6 mm, cw 18.2 mm), Tumokemoke Seamount, 37°27.95–27.97’S, 179°57.28–57.05’E, 474– 435 m, TAN0413/168, 15 Nov 2004;

PARATYPES: NIWA 34979 , 1 male (cl 13.4 mm, cw 17.8 mm), 1 ovigerous female (cl 8.2 mm, cw 11.7 mm), off Curtis Island , Kermadec Islands, 30°17.59’S, 178°25.30’W, 398–412 m, stn K840, 28 Jul 1974 .

Diagnosis. Carapace subpentagonal, 1.3 times wider than long; dorsal surface densely covered with coarse granules and stalked, stellate tubercles (tubercles on highest surfaces of mesogastric, epibranchial and cardiac regions generally flatter than surrounding tubercles). Protogastric region with paired, blunt upright tubercles. Cardiac region with prominent median tubercle. Epibranchial and mesobranchial regions with prominent upright tubercle posteriorly. Anterior branchial margin broadly convex, with 8–10 well-spaced, secondarily tuberculate or spinulate teeth. Lateral angle acute of carapace produced to a slender, granular point. Cheliped surfaces covered with small granules; propodus dorsal margin with 10–12 prominent, tuberculate teeth. P2–5 laterally compressed, surfaces smooth or finely granular near distal ventral margins; merus dorsal margin cristate on P2, partially cristate and partially tuberculate on P3–5; propodi dorsal margin cristate on P2–5; dactyli shorter than propodi, finely setose. Male G1 stout, aperture ovate; distal quarter with small spinules. G2 distal section as long as proximal section, with ‘twist’ at midlength, apex spiniform.

Description. Carapace subpentagonal, 1.3 times wider than long; dorsal surface densely covered with coarse granules and stalked, stellate tubercles (tubercles on highest surfaces of mesogastric, epibranchial and cardiac regions tending flatter). Rostrum with blunt, tapering apex, horizontal; lateral, proximal lobes blunt. Surface of frontal region with median concavity. Protogastric region raised, with pair of blunt, upright tubercles. Meso- and metagastric regions inflated. Cardiac and intestinal region fused into inflated, upraised prominence, with blunt, conical, upright tubercle and low tubercle (indistinct in female) on posterior slope. Epibranchial region with prominent, inflated, oblique swelling, posteriorly with conical, upright tubercle. Mesobranchial region inflated, lower than epibranchial regions, with blunt upright tubercle. Outerorbital margin granular but unarmed. Supra orbital margin lined with subglobular granules. Suborbital margin granular, with blunt, granular, mesial tooth. Hepatic margin with blunt, tuberculate tooth. Anterior branchial margin broadly convex, with 8–10 well-spaced, triangular, secondarily tuberculate or spinulate teeth, decreasing in size posteriorly. Lateral angle acute, produced to a slender, granular point. Posterior branchial margin concave, granular, with blunt, subdistal tooth. Posterior margin tuberculate, with 3 blunt, tuberculate lobes, lateral lobes larger than median lobe. Pterygostomial, sub-branchial and suborbital regions densely granular, most simple, but some stalked and stellate. Subhepatic region excavate. Pterygostomial ridge prominent, cristate, coarsely tuberculate.

Eyestalks with small, globular granules; as wide as cornea. Epistome with median proximal pit and 4 pits along distal margin; surface with sparse, flattened granules, otherwise smooth. Basal antennular segment granular. First free antennal segment wider than long. Second free antennal segment petagonal, granular (immobile though not fused to epistome and suborbital margins). Third and fourth free antennal segments slender, smooth.

Third maxilliped ischiobasis subrectangular, mesial margin smooth, straight, median surface with broad longitudinal groove, surface covered with rounded granules, tending acute towards lateral margins. Merus broadly ovate, about half-length of ischiobasis; with 2 broad, deep concavities; surface irregular, eroded, with coarse tubercles (some stalked) and prominent central compound tubercle. Carpus, propodus and dactylus smooth, concealed by ischium and merus when folded. Exopod dorsal surface coarsely granular, apex not exceeding distal margin of ischium.

Thoracic sternites densely covered with small, round granules; sternites 3–4 with broad, V-shaped depression, with compound tubercle near articulation with cheliped basis; sternite sutures 4/5 and 5/6 medially interrupted; sternite suture 6/7 complete; sternite 8 with median groove; sternite 5 ‘press-button’ positioned anteriorly in both sexes.

Chelipeds subequal, right chela slightly larger, more robust than left; about 3 times carapace length in males, 2 times carapace length in female; surfaces covered with small granules. Ischium anterior margin with 5 or 6 irregular teeth. Merus subtriangular in cross-section; inner margin with 10–12, low, irregular teeth and tubercles; proximal 2/3 of outer margin with acute tubercles and 7 or 8 irregular, conical, tuberculate teeth, longest tooth near meral midlength; dorsal surface with upright tooth near dorsal margin at proximal 1/3 of merus. Carpus surfaces evenly granular, inner margin tuberculate, outer margin with 2 prominent teeth proximal to midlength and smaller distal tooth. Propodus subtrigonal in cross-section; inner margin irregularly tuberculate, distally with slightly flattened, dentate crest; outer margin with 10–12 prominent, tuberculate teeth, of which 4 are about twice as long as remainder; distal margin near dactylar articulation with coarse tubercles and prominent tooth. Fingers coarsely granular, shorter than 1/3 palm length, distal half to third dark brown; occlusal margins of left chela thin, blade-like, occluding; occlusal margins of right chela, blunt, slightly molariform or evenly curved, gaping. Dactylus slightly curved, with low longitudinal carina; dorsal margin tuberculate, with 2 rounded, laterally compressed crests, proximal distinctly larger. Pollex slightly shorter than dactylus, tuberculate.

Ambulatory legs decreasing in length posteriorly; laterally compressed; P2 longest; meri, carpi and propodi laterally compressed, surfaces smooth or finely granular near distal ventral margins; dactyli shorter than propodi, finely setose with corneous apex. P2 merus dorsal margin cristate, except for coarsely dentate proximal fifth; merus ventral margin bicristate; carpus and propodus dorsal margins cristate, unbroken. P3–4 meri dorsal margin cristate distally, coarsely dentate and tuberculate proximally; meri ventral margin with 2 rows of short, irregular crista, laminar teeth and tubercles; carpi and propodi dorsal margins cristate, unbroken. P5 merus dorsal margin cristate distally, coarsely dentate and tuberculate proximally; merus ventral margin with 2 rows of short, irregular crista, laminar teeth and tubercles; carpus and propodus dorsal margins cristate, unbroken.

Male abdomen narrow; surface eroded, rugose, granular; fused somites 3–5 forming subquadrate plate, widest at somite 3, narrowing to somite 5. Somite 6 rectangular, as wide as somite 5; with distal median spine. Telson triangular, 1.3 times wider than long, apex rounded, margins slightly concave; surface granular.

Female abdomen broad, margins convex, widest at somite 5; surface covered with rounded granules, otherwise unarmed; telson triangular, 1.6 times wider than long, apex rounded.

G1 stout, tubular, slightly curved, apex rounded, not inclined mesially, aperture ovate; distal quarter with small spinules; reaching slightly beyond anterior margin of sternite 5. G2 about 1.1 times as long as G1; distal section as long as proximal section, broadly curved distally, with ‘twist’ at midlength, apex spiniform. Female gonopore on sternite 6 simple, subcircular, aperture closed by soft, flap ‘articulating’ along lateral margin of gonopore.

Etymology. Named for Swee Hee Tan, for his very useful advice and considerable expertise in the Parthenopidae .

Remarks. Garthambrus tani sp. nov. is the first parthenopid to be identified from New Zealand waters, although Takeda & Webber (2006) mentioned the presence of an undetermined species each of Platylambrus Stimpson, 1871 and Tutankhamen Rathbun, 1925 from the Kermadec Islands, of which the latter may be referable to G. tani . Garthambrus tani approaches G. stellata ( Rathbun, 1906) ( Taiwan, Hawaii, and French Polynesia) in the dense covering of stellate tubercles on the carapace ( Fig. 27A ) and swollen, peaked metabranchial regions ( Fig. 25B ). The new species is readily distinguished from G. stellata , however, by having smaller, less prominent carapace tubercles, shape of the G1 and ornamentation of the chelipeds and walking legs. The aperture of the G1 of G. tani is ovate rather than narrowly tapering and the apex is not inclined medially (compare Fig. 27E with Ng & Tan 1999: fig. 6A–B). The chelipeds of G. tani are comparatively smoother than in G. stellata , having an even scattering of small tubercles ( Fig. 26E–F ) rather than the dense, coarse tubercles that cover all surfaces (in addition to the tuberculate or dentate margins present in both species). Similarly, the ambulatory legs of G. tani have smooth, rather than densely granular lateral surfaces; and smooth or slightly irregular, rather than tuberculate or prominently dentate, dorsal and ventral margins of the carpi and propodi ( Fig. 27B–D ).

The specimens agree well in most respects. The female differs from males in having shorter chelipeds, less gaping right cheliped fingers, in having lower teeth along the inner margin of the cheliped merus and a less distinct tubercle on the posterior slope of the cardiac-intestinal region. The former two differences are likely to be attributable to sexual dimorphism, whereas the latter two differences are probably related to allometry. Females evidently mature at a small size, with the 8.2 mm cl female paratype carrying numerous ‘black-eyed’ stage eggs of 0.4 mm diamater.

In their brief outline of the fauna of New Zealand seamounts and hydrothermal vents, Clark & O’Shea (2001) mentioned the presence of Tutankhamen sp. (based on the holotype of G. tani ), which Martin & Haney (2005) interpreted to originate from a hydrothermal vent. The type locality of G. tani, Tumokemoke Seamount , however, is not currently known to be an active hydrothermal vent site.

Distribution. Presently known only from Tumokemoke Seamount and the Kermadec Islands, New Zealand; 398– 474 m.

Figures

FIGURE 25. Garthambrus tani sp. nov., male holotype, cl 13.6 mm, cw 18.2 mm (NIWA 6776). A, dorsal habitus. B, carapace, dorsal view.

FIGURE 26. Garthambrus tani sp. nov., male holotype, cl 13.6 mm, cw 18.2 mm (NIWA 6776). A, anterior. B, posterior. C, ventral. D, carapace, right lateral view. E, left chela, oblique anterior view. F, right cheliped.

FIGURE 27. Garthambrus tani sp. nov.. A–G, male holotype, cl 13.6 mm, cw 18.2 mm (NIWA 6776). H, ovigerous female paratype, cl 8.2 mm, cw 11.7 mm (NIWA 34979). A, stalked stellate tubercles (right anterior branchial region). B, right P2. C, right P4. D, right P5. E, right G1, abdominal view. F, right G2, abdominal view. G, male abdomen. H, female abdomen. Scale A = 0.2 mm, B–D, G–H = 2.0 mm, E–F = 0.8 mm.