Mariaplax aspera, Ng, Peter K. L. & Rahayu, Dwi Listyo, 2015

Ng, Peter K. L. & Rahayu, Dwi Listyo, 2015, Notes on Hexapodidae (Crustacea, Brachyura) from Indonesia and Malaysia, with description of a new species of Mariaplax Rahayu & Ng, 2014, from Lombok, Indonesia, Zootaxa 3981 (1), pp. 125-137 : 135-137

Mariaplax aspera n. sp.

( Figs. 6 G, H, 7)

Material examined. Holotype, female (6.4 × 4.4 mm) ( MZB Cru 4212), Medana, Lombok Utara, Indonesia, from hole in seagrass bed, using yabby pump, coll. D.L. Rahayu et al., 12 May 2014.

Etymology. Named after the Latin for “rough”, alluding to the granular surfaces of the carapace.

Diagnosis of female holotype. Carapace subquadrate, wider than long, width 1.5 times length, dorsal surfaces almost entirely covered with small tubercles, regions indistinct ( Fig. 7 A); anterolateral margin arcuate, lined with small rounded granules; posterolateral margin with slight protuberance; posterolateral corner with angled prominence over base of posterior pereopods ( Fig. 7 A); front deflexed ( Fig. 7 B); orbit distinct, eye small, slightly movable, cornea pigmented ( Fig. 7 B); suborbital, overall pterygostomial, and subhepatic regions covered with scattered granules ( Fig. 7 B, C); pterygostomial region with oblique striae, dense setae under striae adjacent to Milne Edwards opening ( Fig. 7 B, C); third maxillipeds broad, completely covering buccal cavity; outer surfaces of ischium, merus covered with numerous small granules; ischium subequal in length to merus, with gently rounded mesial margin ( Figs. 6 G, 7C); chelipeds approximately symmetrical, slightly gaping when fingers closed; outer surfaces granulated ( Fig. 7 A, B); P2–P4 short, stout, outer surfaces with numerous distinct small granules, short setae, P3 stoutest, longest, longitudinal groove on merus barely visible ( Figs. 7 A); thoracic sternum broad ( Fig. 7 C, D), sternites 1, 2 fused, separated from sternite 3 by distinct ridge; sternite 3 separated from sternite 4 by distinct ridge; sternites 4–7 distinct, separated by distinct sutures; sternite 8 not visible; vulvae large, without opercular cover, on anterior half on sternite 6, opening lunate ( Fig. 7 D); abdomen subovate, with 6 free somites, telson; somite 6 longest, trapezoidal, subequal in length to telson, telson subtriangular with rounded tip ( Figs. 6 H, 7C).

Color. Carapace light brown, mottled red and dark brown; chelipeds and P2−P4 light brown.

Remarks. This new species resembles M. narusei Rahayu & Ng, 2014, from Japan in having short P2–P4 with the merus possessing a barely indiscernible median groove on the outer surface. The two species, however, are easily separated. The surfaces of the third maxilliped of M. narusei is relatively less granular ( Rahayu & Ng 2014: fig. 40D) than in M. aspera n. sp. ( Fig. 6 H); and the telson of the female is equal in length to somite 6 of the abdomen ( Rahayu & Ng 2014: fig. 40H) (telson slightly shorter than somite 6 in M. aspera n. sp., Figs. 6 H, 7C). The carapace of M. narusei is also proportionately broader (1.7 times as broad as long versus 1.5 as broad as long in M. aspera n. sp., Figs. 7 A), however, this difference should be regarded with caution as the specimens of M. narusei examined by Rahayu & Ng (2014) are larger than the present species (9.6–12 × 5.8–7.1 mm versus 6.4 × 4.4 mm in M. aspera ), and carapace proportion does vary with the size of the specimen.

The mesial margin of the ischium of the third maxilliped is rounded, resembling that of the genus Hexapinus , but the ischium is proportionately broader in Hexapinus , with the distomesial margin usually more expanded. In M. aspera n. sp., however, the ischium of the third maxilliped is as broad as the merus with the mesial margin not distinctly expanded. This is one of the key diagnostic characters for Mariaplax Rahayu & Ng, 2014 ( Rahayu & Ng 2014: 424). Fourteen Mariaplax species are currently known from the Indo-West Pacific region, though none have been previously reported from Lombok and neighbouring islands. Lombok has two hexapodid species: Hexapinus simplex and H. latus ( Rahayu & Ng 2014) .

Figures

FIGURE 7. Mariaplax aspera n. sp., holotype female (6.4 × 4.4 mm) (MZB), Lombok, Indonesia. A, overall habitus; B, frontal view of cephalothorax and chelae; C, thoracic sternum and abdomen; D, sternoabdominal cavity and vulvae (v).

FIGURE 6. A – F, Hexapinus latipes (De Haan, 1835), male (20.9 × 12.5 mm) (SMF ZMG 160 a), Ambon, Indonesia; G, H, Mariaplax aspera n. sp., holotype female (6.4 × 4.4 mm) (MZB), Lombok, Indonesia. A, ventral view of left G 1; B, dorsal view of left G 1; C, ventral view of distal part of left G 1; D, dorsal view of distal part of left G 1 (setae not drawn); E, left G 2 (ventral view); F, distal half of left G 2 (dorsal view); G, left third maxilliped; H, female abdomen. Scales: A, B, E, G, H = 1.0 mm; C, D, F = 0.5 mm.