Mirograpsus asper, Komai & Fujita, 2018

Komai, Tomoyuki & Fujita, Yoshihisa, 2018, A new genus and new species assigned to Macrophthalmidae (Decapoda: Brachyura: Thoracotremata) from the Ryukyu Islands, Japan, Zootaxa 4531 (1), pp. 109-116 : 111-115

publication ID	https://doi.org/ 10.11646/zootaxa.4531.1.5
publication LSID	lsid:zoobank.org:pub:237FD9CC-77C2-432F-B912-FBB2AC4F03FB
DOI	https://doi.org/10.5281/zenodo.5951360
persistent identifier	https://treatment.plazi.org/id/03B2878D-DC6D-FF85-FF5F-FF1C285FF936
treatment provided by	Plazi
scientific name	Mirograpsus asper
status	sp. nov.

Treatment

Mirograpsus asper View in CoL n. sp.

[New Japanese name: Kimen-doro-gani]

( Figs. 1–4 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 )

Material examined. Holotype: male (5.8 x 5.1 mm), northwest part of Kabira Bay , Ishigaki Island , Yaeyama Islands, Ryukyu Islands, intertidal sand and mud flats (Monitoring Sites 1000 site number TFKBR-AU, around N24.45546, E124.13954), 19 August 2017, coll. H. Karimata and H. Kubo, CBM-ZC 14607. GoogleMaps

Description. Carapace ( Figs 1 View FIGURE 1 , 2A View FIGURE 2 , 3 View FIGURE 3 ) flattened, subquadrate, 1.14 times as long as wide; regions well defined, gastric, cardiac, intestinal and branchial regions markedly elevated, hepatic regions shallowly depressed; gastrocardiac groove broad; surface microscopically granular in general. Cardiac region with paired blunt, rounded prominences ( Fig. 2B View FIGURE 2 ). Branchial regions slightly inflated, each with 1 conspicuous tubercle laterally ( Fig. 2B View FIGURE 2 ). Lateral margins slightly diverging in anterior half, subparallel in posterior half, point of greatest carapace breadth at posterior one-third (above bases on pereopods 3). Three anterolateral teeth, first (external orbital angle) directed anteriorly, subacute; second tooth well demarcated, but blunt; third smaller than second, tubercle-like. Short, oblique, granulate crest present adjacent to posterolateral carapace margin. Front prominent, widened posteriorly, not constricted; anterior width approximately equal to width of orbit, 0.3 times external orbital width; anterior margin in dorsal view deeply bilobed with wide median groove, lateral margins slightly sinuous, noticeably upturned. Upper orbital margin sinuous ( Fig. 2A View FIGURE 2 ), nearly transverse; lower orbital margin gently convex in ventral view, lined with row of minute granules ( Fig. 2C, D View FIGURE 2 ), inner orbital tooth blunt ( Fig. 2C View FIGURE 2 ); small, but distinct granular tubercle just below inner orbital tooth ( Fig 2C, D View FIGURE 2 ). Postfrontal lobes absent. Pterygostomial region microscopically granular, with weak oblique ridge extending from anterolateral angle of buccal cavity. No setae along carapace margins.

Eyes ( Fig. 2A, C View FIGURE 2 ) large, just reaching external orbital tooth, constricted medially, slightly narrowing distally; cornea nearly as long as eyestalk measured along ventral margin; dorsal tubercle very low, with microscopic granules.

Antennules ( Fig. 2A, C View FIGURE 2 ) separated by triangular septum narrowing toward frontal margin; basal article inflated, surface microscopically granular; flagellum lying slightly obliquely. Antennae ( Fig. 2A View FIGURE 2 ) very short, lying within orbital hiatus; flagellum greatly reduced, consisting of only 2 minute articles, terminal article tapering, with long apical filamentous seta.

Epistome ( Fig. 2C View FIGURE 2 ) quite broad, lower edge with 3 bluntly triangular lobes, median lobe slightly broader than laterals and less projecting; surface of median lobe shallowly depressed. Short median carina present on anterior part of buccal cavity just below epistomal median lobe.

Maxilliped 3 ( Fig. 2E View FIGURE 2 ) without median hiatus, fully closing buccal cavity. Ischium outer surface with minute granules and median groove; lateral and distal margins concave, laterodistal angle produced into triangular projection. Merus slightly shorter than ischium (measured along lateral margin); outer surface also minutely granular, with 2 shallow grooves; lateral margin somewhat expanded, broadly rounded; distal margin concave with carpus emerging more or less centrally. Carpus short, not reaching mesial margin of merus. Propodus subquadrate, with tuft of setae at flexor distal angle. Dactylus tapering, distinctly narrower than propodus. Exopod slender, width less than half of width of ischium, distal part concealed by lateral margin of merus; flagellum 2-articulated, concealed by merus.

Chelipeds ( Figs. 1 View FIGURE 1 , 3 View FIGURE 3 , 4A, B View FIGURE 4 ) subequal, similar. Ischium with inner surface inflated, granular. Merus covered with microscopic granules except for inner surface; inner surface slightly concave, smooth, with row of moderately short setae adjacent to lower margin; upper margin carinate, gently arcuate, unarmed, subterminally with shallow notch. Carpus unarmed; surfaces covered with microscopic granules; outer surface convex; inner surface with small patch of short to long setae dorsally. Chela moderately robust, about twice as long as high; upper and outer surfaces microscopically granular; lower margin (including fixed finger) bluntly carinate, gently sinuous, fixed finger not much deflexed; inner surface with mat of soft plumose setae; fingers pointed distally, tip crossing; occlusal margins each with row of small triangular teeth of subequal in size; dactylus gently curving, 0.84 times as long as palm, upper surface microscopically granular.

Ambulatory legs (pereopods 2–5) ( Figs. 1 View FIGURE 1 , 4 View FIGURE 4 C–F) moderately long, relatively slender, somewhat compressed; length: pereopod 5 <pereopod 2 <pereopod 4 <pereopod 3. Meri slightly narrowing distally, each without subdistal spine on anterior margin, but with shallow transverse groove subdistally; anterior margins with sparse setae at least proximally; length/width 3.1 in pereopod 2, 3.6 in pereopod 3, 3.5 in pereopod 4, 3.3 in pereopod 5. Surfaces of meri, carpi and propodi microscopically granular. Propodi slightly narrowing distally, naked (pereopods 2 and 3) or bearing row of sparse setae (pereopods 4 and 5); length/width 3.1 in pereopod 2, 3.7 in pereopod 3, 3.3 in pereopod 4, 1.6 in pereopod 5. Dactyli slender, slightly curved, each terminating in small corneous claw, with 6 (pereopods 2–4) or 5 (pereopod 5) longitudinal carinae; dactylus length/propodus length 1.0 in pereopod 2, 0.7 in pereopod 3, 0.9 in pereopod 4, 1.7 in pereopod 5.

Thoracic sternum ( Fig. 2F View FIGURE 2 ) moderately wide. Sternites 1 and 2 fused, narrowly triangular. Sternite 3 broadly subtrapezoidal, with row of setae on anterior margin; surface slightly depressed. Suture between sternites 4/5 slightly sinuous; those between sternites 5/6. 6/7 and 7/8 nearly straight. Sternite 4 largest, surface minutely granular, with deep depressions anterolaterally; episternites subtriangular, incompletely fused to sternite 4. Sternites 5–8 becoming smaller toward posterior, surfaces nearly smooth (sternites 5–7) or minutely granular (sternite 8); respective episternites subtriangular, completely fused. Sterno-pleonal cavity ( Fig. 2F View FIGURE 2 ) reaching boundary between sternites 3/4; edges bordered with minute granules; press-button of pleon-locking mechanism with small papilla-like knob on anterior edge of thoracic sternite 5. Penis sternal, papilla-like, not calcified.

Pleon ( Fig. 2G View FIGURE 2 ) narrowing toward telson, not fully occupying entire space between coxae of pereopods 5. Somite 1 widest, with produced distolateral angles; surface with granulated transverse ridge running over entire width. Somite 2 very short, narrower than somites 1 and 3. Surfaces of somites 3–6 smooth. Somites 3 and 4 subrectangular, lateral margins slightly convex. Somites 4–6 functionally fused; suture between somites 4/5 distinct on external surface while not discernible in internal surface, suture between 5/6 discernible only in medial part on external surface, not discernible on internal surface; somite 6 with low but distinct, angular projection on each lateral margin, making pleomere 6 slightly wider than pleomere 5. Telson subtriangular, terminal margin rounded, 1.45 times as wide as long, subequal in length to pleomere 6.

Gonopod 1 ( Fig. 2H, I View FIGURE 2 ) not reaching midlength of sternite 4, slightly curved outward, gradually tapering distally to very short chitinous process; distal part with rows of moderately short setae; ventral and dorsal surfaces with irregular rows of sparse short setae. Gonopod 2 ( Fig. 2J View FIGURE 2 ) less than 0.2 length of gonopod 1, sinuous, somewhat expanded basally, terminal lobe rounded.

Colour in life. Fig. 1 View FIGURE 1 . Carapace dorsum light mottled brown generally, with dark brown median longitudinal band and oblique branches of same color on cardiac region. Chelipeds generally whitish, with tint of brown on meri and carpi; dactylus with small dark brown spot on upper surface medially. Ambulatory legs also generally white, with tint of light brown on meri; meri each with dark brown spots medially; propodi each with dark brown band medially.

Habitat. The location where the holotype of Mirograpsus asper n. gen., n. sp. was collected was on sandy and muddy tidal flats on the northwest part of Kabira Bay, with a small river flowing in, and with mangrove plants. The crab was found walking around on the surface of the sandy tidal flat, without evidence of burrowing. The syntopic decapod fauna includes Diogenes avarus Heller, 1865 (Anomura: Diogenidae ), Diogenes leptocerus Forest, 1957 (Anomura: Diogenidae ), Mictyris guinotae Davie, Shih & Chan, 2010 (Brachyura: Mictyridae ), Scopimera ryukyuensis Wong, Chan & Shih, 2010 (Brachyura: Dotillidae ) and Macrophthalmus (Macrophthalmus) convexus Stimpson, 1858 (Brachyura: Macrophthalmidae ).