Mariaplax pitrai Rahayu & Widyastuti 2018, n. sp.
Creators: name: Rahayu, Dwi Listyo
name: Widyastuti, Ernawati
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Hexapodidae
Mariaplax
Mariaplax pitrai

description: Mariaplax pitrai n. sp.
(Figs. 3–5)
Material examined. Holotype, female (4.0 × 2.8 mm) (MZB Cru 4681), st. B5, Pulau Damar Kecil, 6°00.708'S, 106°85.084'E, mud substrate, coll. P. Widianwari, 6 September 2014. Paratypes, 2 females (4.0 × 2.7 mm, 4.0 × 2.8 mm) (ZRC), same locality as holotype.
Comparative material. Mariaplax chenae Rahayu & Ng, 2014, 1 female (5.3 × 3.5 mm) (ZRC 2012.1021), station 23 (WC38B-10), coastal water outside Dongtou Island, Zhejiang Province, East China Sea, 4 m, soft mud, coll. AT, Y. Cui & Y. Wu, 8 October 1979.
Diagnosis. Carapace 1.4 as broad as long, region indistinct, dorsal surface granulated; third maxiliped with ischium slightly longer than merus, mesial margin straight; chelipeds subequal, covered by small tubercles; P2–P4 relatively long, slender, meri more than twice length of carpi, each with longitudinal groove on lateral surface; vulva large, without cover, positioned on anterior half of sternite 6, opening rounded, pleon ovate, with 6 free somites, telson; somite 6 longest, somite 4 broadest, telson subtriangular with rounded tip.
Description. Carapace subquadrate, about 1.4 times as broad as long; regions indistinct, with median Hshaped shallow depression; deep indentations on branchial region; dorsal surface entirely covered with tubercles (Figs. 3A, B, 5A). Anterolateral margin arcuate; posterolateral corner with feeble angle over base of posterior pereopods. Front deflexed, divided into 2 lobes, not projecting beyond outer edge of orbits. Orbit distinct, transverse; eye small, slightly movable, cornea black, narrower than peduncle (Fig. 3A, B). Pterygostomial region with row of oblique striae and scattered tubercles (Figs. 4A).
Epistome longitudinally narrow; posterior margin concave with broadly triangular median projection.
Third maxillipeds broad, covering buccal cavity (Figs. 4A, B, 5C); ischium slightly longer than merus, mesial margin straight, some granules dorsomesially; merus slightly wider than ischium; carpus, propodus and dactylus cylindrical; dactylus longer than propodus; combined length of dactylus, propodus and carpus slightly shorter than that of merus and ischium; exopod relatively narrow, width about 0.4 times width of ischium, flagellum well developed.
Chelipeds stout, subequal, right slightly larger than left. Major chela (Figs. 3C, 5D) with narrow gap when fingers closed, with large tooth at cutting edge of dactylus and fixed finger; dactylus with row of sparse setae on proximal third of upper margin, outer surface of dactylus and fixed finger with widely-spaced tubercles proximally; palm slightly wider than long, outer surface covered with tubercles, short sparse setae on upper and lower margins; carpus covered with tubercles on outer surface margin, slightly setose; merus short, unarmed, fringe of setae dorsomesially. Minor chela (Figs. 3D, 5E) without gap when fingers closed; armament similar to major chela.
P2–P4 relatively long, slender, P3 longest. P2 (Figs. 3A, B, 5F) most slender, dactylus slightly upcurved, fringe of setae on upper and lower margins, longer than propodus; short setae and row of tubercles on upper and lower margins of propodus; carpus slightly longer than propodus, unarmed, tufts of setae on upper margin; upper and lower margins of merus with tufts of short setae, outer surface with longitudinal median groove, lower margin with rows of tubercles. P3 (Figs. 3A, B, 5G) stouter, longer than P2, setation denser and longer than on P2 and P4. P4 (Figs. 3A, B, 5H) stouter than P3, dactylus upcurved; meri of P3 and P4 about 3.4 times as long as broad, outer surface with rows of tubercles separated by shallow longitudinal sulcus; denser, closely-spaced tubercles on P4.
Thoracic sternum broad (Fig. 4A–C), sternites 1 and 2 fused, separated from sternite 3 by distinct ridge; sternite 3 and 4 separated by distinct ridge laterally, sternites 4–7 well developed, separated from each other by distinct suture; sternite 8 exposed, small, subtriangular, slightly shorter than pleonal somite 1; sternopleonal cavity reaches base of sternite 3. Female pleon relatively narrow with 6 free somites and telson (Fig. 4A, B), covered by tubercles; telson subtriangular, distal margin rounded, length and basal width subequal; female vulvae large (Fig. 4C), without opercular cover, on anterior half of sternite 5, opening subcircular. Male unknown.
Etymology. Named after the late Pitra Widianwari, researcher at Research Center for Oceanography, Indonesian Institute of Sciences (LIPI), who collected the specimens.
Remarks. The subquadrate carapace with closely-spaced tubercles of M. pitrai n. sp. resembles that of M. chenae. Comparison with a female of M. chenae of slightly larger size, shows that the two species have the same relatively narrow pleon, but the shape and position of vulvae is different. The vulvae of M. chenae are slightly subtriangular and well separated, positioned more laterally at the middle of sternite 5̄6 (Fig. 4D), while in M. pitrai n. sp. the vulvae are sub-circular, positioned closer to each other, and positioned more upward near the suture of sternite 4̄5 (Fig. 5C). Furthermore M. chenae has the telson shorter than somite 6 (Fig. 5F; Rahayu & Ng, 2014: fig. 25K), while in M. pitrai n. sp. the telson is as long as somite 6 (Fig. 5A, B).
The long and slender pereopods with the merus of P4 more than three times as long as broad, and the subquadrate carapace places M. pitrai n. sp. close to M. mica Rahayu & Ng, 2014, and M. propinqua Rahayu & Ng, 2014. The females of M. propinqua are unknown, but the rectangular carapace, the large, closely-spaced tubercles on the carapace and pereopods, with long, dense setae on the P2–P 4 in M. propinqua, separate this species from M. pitrai which has more squarish carapace with small, widely-spaced tubercles on the carapace and pereopods, and light setation on P2–P4. Mariaplax mica has a broad pleon, with the telson longer than broad at the base, the merus of the third maxilliped is as long as the ischium, with the subproximal part of the ischium expanded, while M. pitrai n. sp. has a narrower pleon with the telson as long as broad at the base, the merus of the third maxilliped is shorter than the ischium, and the ischium is not expanded subpropximally.
Distribution. Found only in Pulau Damar Kecil, Pulau Seribu, Jakarta Bay, Indonesia.
description: Published as part of Rahayu, Dwi Listyo & Widyastuti, Ernawati, 2018, Additions to the Indonesian crab fauna of the genus Mariaplax Rahayu & Ng, 2014, and notes on Hexapus timika Rahayu & Ng, 2014 (Crustacea, Decapoda, Brachyura, Hexapodidae), pp. 231-246 in Zootaxa 4379 (2) on pages 235-238, DOI: 10.11646/zootaxa.4379.2.5, http://zenodo.org/record/1175468