Linnaeoxantho acanthomerus ( Rathbun, 1911 )

Mendoza, Jose Christopher E., Clark, Paul F. & Ng, Peter K. L., 2012, The identity of Pilumnoplax acanthomerus Rathbun, 1911 (Crustacea: Decapoda: Brachyura: Xanthidae), with new records from the central and western Pacific *, Zootaxa 3367 (1), pp. 211-221 : 215-219

publication ID	https://doi.org/ 10.11646/zootaxa.3367.1.20
persistent identifier	https://treatment.plazi.org/id/6E6E87DD-FFC0-FF8A-93F4-B363FE9EFD51
treatment provided by	Felipe
scientific name	Linnaeoxantho acanthomerus ( Rathbun, 1911 )
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Linnaeoxantho acanthomerus ( Rathbun, 1911)

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

Pilumnoplax acanthomerus Rathbun, 1911: 237 , pl. 18 fig. 13. — Guinot 1969: 689. — Serène & Lohavanijaya 1973: 69. — Manning & Holthuis 1981: 161.

Neopilumnoplax View in CoL ? acanthomerus . — Serène 1968: 90.

Linnaeoxantho acanthomerus . — Števčić 2005: 45.

Linnaeoxanthus [sic] acanthomerus — Ng et al. 2008: 203 (list). — Ng & Castro 2010: 25.

Material examined. Types: holotype ♂, 12.9 × 8.5 mm, paratype 1 ♀ ovig., 15.0 × 10.1 mm ( USNM 41353 About USNM ), stn E 21, 54 m (30 fms), Amirante Islands, coll. J. Stanley Gardiner, H.M.S. Sealark, 17 Oct. 1905 . Additional material: 1 ♂, 7.1 × 5.5 mm ( ZRC 2012.0160 View Materials ), “ Dive Ola ”, scuba, 24 m, Kumejima Is., Ryukyu Islands, Japan, coll. P.F. Clark et al., 9 Nov. 2009 ; 1 ♀, 11.0 × 7.5 mm ( UF 10556 ), outer reef slope, from dead Pocillopora head, 10–15 m, Tabuaeran Atoll , Kiribati, Line Islands, coll. G. Paulay & N. Knowlton, 12 Aug. 2005 .

Description of holotype. Carapace ( Fig. 2A View FIGURE 2 ) subhexagonal, width about 1.5 × length; dorsally slightly convex, dorsal surface covered with several, discrete, round granules, larger on anterior third; regions mostly not well defined, anterior part of 2M, 3M well delineated by narrow, shallow grooves, 2M undivided. Front relatively wide, about 0.4 × maximum carapace width; slightly deflexed ventrally; separated from orbits by deep notch; separated into 2 lobes by shallow median notch; anterior margin sinuous, lateral lobes moderately prominent, with distinct, neat row of granules immediately posterior. Anterolateral margin about half length of posterolateral margin; armed with 4 acute, projecting teeth, including exorbital tooth; first (exorbital) tooth broadest at base, fourth smallest, spiniform; carapace widest at level of third tooth; posterolateral margin straight; central portion of posterior margin slightly concave. Suborbital, subhepatic, pterygostomian regions granulate.

Orbits ( Fig. 2A View FIGURE 2 ) large, margins finely granulate, subcristate; superior, inferior orbital margins each with distinct notch, continuing posteriorly as short fissure; eyes large, ocular peduncles short, stout, corneas well developed. Antennular fossae ( Fig. 3B View FIGURE 3 ) large, antennules folding transversely. Basal article of antennae ( Fig. 3B View FIGURE 3 ) subrectangular, with small distolateral extension entering orbital hiatus; antennal flagellum long, exceeding exorbital angle by one-third of its length. Epistome ( Fig. 3B View FIGURE 3 ) broad; central region of posterior margin nearly straight, lateral regions of posterior border convex. Endostome without oblique ridges. Mxp3 ( Fig. 3A, B View FIGURE 3 ) smooth, slender, not completely closing buccal cavity; merus subquadrate, median length about 0.4 × median length of ischium; ischium subrectangular, with shallow submedian sulcus; exopod long, subrectangular, with prominent mesial projection subdistally.

Thoracic sternum ( Figs. 3A View FIGURE 3 , 4B View FIGURE 4 ) broad, finely granulate; sternites 1, 2 fused, large, separated from sternite 3 by distinct suture 2/3; sternites 3, 4 almost completely fused except at lateral edges; sternite 4 broad, without visible median line; sternites 5, 6 similar in shape, sternite 7 with anterior portion much larger than episternite, sternite 8 completely covered by abdominal somite 3; sternal press-button on posterior half of sternite 5, closer to suture 5/6; sutures 4/5, 5/6 interrupted medially, sutures 6/7, 7/8 complete; median, membranous, uncalcified region at level of suture 6/7; median line only visible at level of sternites 7, 8.

Chelipeds (P1) ( Fig. 1 View FIGURE 1 , 2 View FIGURE 2 , 3E, F View FIGURE 3 ) unequal. Meri finely granulate, long, distal portions well exceeding margins of carapace; anterior margin armed with four conspicuous spines distributed along entire length. Carpus coarsely granulate on external surface; with 2 prominent spines on inner angle, 1 on top of the other; large conical granules interspersed on dorso-distal and dorso-internal margins. Major chela broad, flattened; superior margin of palm with double row of conical granules; internal and external surfaces of palm finely granulate; fingers about half length of palm, tips strongly recurved, with discrete, small tufts of stiff setae; pigment localized throughout length of fingers, except tips, also on distal fourth of palm; dactylus with dorsal keel and longitudinal groove on both external and internal surfaces; cutting margin of dactylus with several low teeth, cutting margin of fixed finger with one broad, molariform tooth, set apart from distal tip by deep notch. Minor chela nearly identical in form but smaller.

Ambulatory legs (P2–P5) ( Figs. 1 View FIGURE 1 , 2 View FIGURE 2 , 4D, E View FIGURE 4 ) relatively long, with long setae; P2, P5 shortest, P3, P4 longest; total length of P4 about 1.5 × maximum carapace width. Meri flattened, length about 2.7 × width; anterior margin armed with several spines throughout entire length; posterior margin with strong spine subdistally on P2, P3, absent in P4, P5. Carpi, propodi similarly spinose on anterior margins. Dactyli straight, ending in chitinous claw. Short, stiff spiniform setae on posterior margins of propodi and on anterior and posterior margins of dactyli.

Abdomen ( Fig. 3A View FIGURE 3 , 4C View FIGURE 4 ) short, tip of telson reaching just posterior to level of coxo-sternal condyles of P1 coxae. Abdominal somites 1, 2 (ab 1, 2) trapezoidal, width 6.0–8.0 times length; somites 3–5 (ab 3–5) fused, lateral margins greatly concave, vestiges of sutures visible externally as small lateral notches; posterolateral regions of ab 3 with cupuliform depression, locking with episternite 7 in closed abdomen; somite 6 (ab 6) subrectangular, width about 1.8 times length, lateral margins slightly concave. Telson subtriangular, tip rounded, lateral margins slightly convex; subequal in length to ab 6.

G1 ( Figs. 4F–H View FIGURE 4 ) short, stout, curved; distal tip reaching just beyond level of sternal suture 5/6, into small, shallow, transverse depression; distal half covered with conical granules, short spiniform setae towards distal tip; distal tip bilobate, without long, plumose subterminal setae. G2 ( Fig. 4I View FIGURE 4 ) nearly straight; slightly more than onethird length of G1; terminal process about 0.3 times total length. Penis relatively short ( Fig. 4B View FIGURE 4 ) emerging from large gonopore, located just anterior to coxo-sternal condyle of P5.

Female morphology. Similar in most respects to male (see Figs. 2B, C View FIGURE 2 , 3B View FIGURE 3 ), except for sexual characters; abdomen broader, all somites and telson freely articulated; vulvae ( Fig. 3D View FIGURE 3 ) moderate in size, oval, positioned on thoracic sternite 6, mid-way between sutures 5/6, 6/7, membrane nearly completely covering gonopores. Chelipeds, in particular meri, relatively shorter than in the male; dark pigmentation limited to fingers of chela.

Coloration ( Fig. 1 View FIGURE 1 ). Carapace reddish-brown, symmetrically specked with yellow on anterior regions and anterolateral margins. Cornea of eyes also reddish-brown. Chelipeds same color as carapace, meri banded alternately with reddish-brown and dirty white; fingers dark brown except, at tips which are white, dark brown pigment extending onto palm in males. Ambulatory meri banded reddish-brown and dirty white, with dirty white bands at joints of carpi, propodi and dactyli. Long, stiff setae on ambulatory legs yellow. See also a colour photo of an uncollected specimen from Indonesia ( Humann & DeLoach 2010: 185).

Remarks. The occurrence of Linnaeoxantho acanthomerus in the Ryukyu and Line Islands ( Figs. 1 View FIGURE 1 , 2C, D View FIGURE 2 ), including one photographic record from Indonesia (no specimens collected; Humann & DeLoach, 2010), significantly widens the range of this species. The type specimens were dredged from a depth of about 54 m, but the new material reveals that this species also occurs at shallower depths (depth range: 10–54 m). From the notes of the collectors of the new material it is also apparent that this species can be found amongst living or dead corals on reef slopes.

Kingdom	Animalia
Phylum	Arthropoda
Class	Malacostraca
Order	Decapoda
Family	Xanthidae
Genus	Linnaeoxantho