Tiwaripotamon nganima Ng, 2024, n. sp.
Creators: name: Ng, Peter K. L.
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Potamidae
Tiwaripotamon
Tiwaripotamon nganima

description: Tiwaripotamon nganima n. sp.
(Figs. 1–5)
Material examined. Holotype: male (59.3 × 43.6 mm) (ZRC 2022.0810), forest between Huu Lung and Lang Son, northern Vietnam, ca. 21.63°N 106.46°E, coll. Nguyen Van Quang, 24 May 2001. Paratypes: 3 males (41.5 × 31.3 mm, 49.3 × 35.2 mm, 54.2 × 40.6 mm), 1 female (53.1 × 39.9 mm) (ZRC 2022.0811), same data as holotype.
Diagnosis. Carapace subquadrate, wider than long (Figs. 1A, 2A–C); epigastric cristae very low, postorbital cristae not visible (Figs. 1A, 2A–C); external orbital tooth broadly triangular, low but usually visible, separated from anterolateral margin by indentation or low cleft (Fig. 2A–C); epibranchial tooth small but visible, rest of anterolateral margin subcristate, gently serrrate (Fig. 2A–C); suborbital margin convex, smooth, without inner tooth; suborbital region smooth, subhepatic, pterygostomial and sub-branchial regions weakly rugose to smooth (Figs. 1C, 2D, E, H); posterior margin of epistome with median lobe prominent, triangular to more rounded but distinctly projecting beyond lateral margins (Figs. 1C, 2D–G). Male thoracic sternites prominently punctate (Figs. 1B, 2H, 3D); tubercle of male pleonal locking mechanism on posterior third of somite 5 (Figs. 1B, 2H, 3D). Ambulatory legs relatively long (Figs. 1A, B, 3C). Male pleon proportionately more quadrate, somites 3 and 4 relatively less wide (Fig. 3F, G). G1 with subterminal segment strongly curved outwards, outer margin forming deep concavity; terminal segment sharply tapering, distinctly upcurved, outer margin of basal part dilated, forming distinct swelling (Figs. 4A–D, 5A–D). Vulva large, ovate and opens obliquely inwards, occupying most of sternite 6, gently pressing onto the suture with sternite 5 (Fig. 4G).
Description of holotype male. Carapace subquadrate, wider than long; dorsal surfaces smooth, regions poorly demarcated, cervical grooves barely visible; H-shaped gastro-cardiac depression shallow but discernible (Figs. 1A, 2A); dorsal surface (including branchial regions) gently convex, gently inflated (Figs. 1A, C, 2A,D); epigastric cristae very low, marked by low, short striae; postorbital cristae not visible (Figs. 1A, 2A). Frontal margin gently sinuous, lobes not well marked, appears almost entire in dorsal view, level with tips of external orbital tooth in dorsal view; median part distinctly deflexed; contiguous with supraorbital margin (Figs. 1A, 2A, D). Supraorbital margin gently sinuous, without clefts or fissures (Figs. 1A, 2A). External orbital tooth low, broad, outer margin longer than inner margin; barely demarcated from anterolateral margin by indentation (Fig. 3A); epibranchial tooth low hardly visible, rest of anterolateral margin convex, subcristate, serrate; posterolateral margin gently sinuous, converging towards gently convex posterior carapace margin (Figs. 1A, 2A). Orbits ovate, large; eyes completely filling space; cornea large, peduncle not elongate (Figs. 1C, 2A, D). Antennules longitudinally narrow, folding laterally (Figs. 1C, 2D); antennae short, not extending beyond orbit (Figs. 1C, 2D). Epistome longitudinally narrow; posterior margin with broadly triangular median lobe, separated from gently sinuous lateral margins by fissure (Figs. 1C, 2D, F). Suborbital margin convex, smooth, without inner tooth; suborbital region smooth, subhepatic, pterygostomial and sub-branchial regions weakly rugose to smooth (Figs. 1C, 2D, H).
Third maxillipeds relatively short; merus shorter and narrower than ischium, surface slightly rugose; ischium subquadrate with no visible median sulcus; exopod short, curved, reaching to one-third length of merus, with short flagellum shorter than merus width (Figs. 1C, 2H, 3B).
Chelipeds elongate; left one prominently larger (Figs. 2A–C, 3A). Basis-ischium with granules on ventral margin; ventral margins of merus lined with tubercles, dorsal margin uneven, distinctly rugose; carpus with long sharp spine on inner angle, surface slightly rugose; outer surface of chela almost smooth, surface of fingers punctate; fingers longer than palm; fingers gently curved with large cutting teeth evenly spread out (Figs. 1A–C, 3A).
Ambulatory legs relatively long; second leg longest, fourth leg shortest; merus with dorsal margin subcristate, margin uneven but not serrate; carpus with subdorsal ridge; propodus long, with shallow median sulcus; dactylus gently curved (Figs. 1A, B, 3C).
Thoracic sternites 1 and 2 completely fused forming triangular plate with convex lateral margins; separated from sternite 3 by straight deep suture; sternites 3 and 4 fused except for shallow lateral groove that is medially interrupted, surface of sternites punctate (Figs. 1B, 2H, 3D). Somite 8 not visible when pleon closed. Sternopleonal cavity reaching to imaginary line connecting submedian part of coxae of chelipeds, distal part subcristate; tubercle of male pleonal locking mechanism on posterior third of somite 5 (Figs. 1B, 2H, 3D).
Pleon broadly triangular; somite 1 longitudinally narrow, reaching to edges of coxae of fourth ambulatory legs; somite 2 slightly wider than somite 1; somite 3 widest; somites 4 and 5 trapezoidal; somite 6 sub-rectangular, wide; telson wide, lateral margin gently convex (Figs. 2H, 3E, F).
G1 relatively slender, subterminal segment strongly curved outwards, outer margin forming deep concavity; terminal segment clearly separated from subterminal segment, sharply tapering, distinctly upcurved, outer margin of basal part prominently dilated, forming distinct swelling (Figs. 4A–D, 5A–D). G2 subequal in length to G1, distal segment two-thirds length of basal segment (Figs. 4E, 5E).
Females and variation. The female specimen agrees with adult males in all aspects except for its more slender and shorter chelipeds. The pleon is ovate and covers almost the entire surface of the thoracic sternum when closed, with the telson semicircular with strongly convex lateral margins (Fig. 4F). The vulva is large, ovate and opens obliquely inwards, occupying most of sternite 6, gently pressing onto the suture with sternite 5 (Fig. 4G).
The series of specimens of T. nganima n. sp. show that some characters are variable. The median lobe of the posterior margin of the epistome varies in strength, although it is always distinctly projecting beyond the lateral margin; being triangular in the holotype male (Fig. 2F) or with the tip more rounded in others (Fig. 2G). The frontal margin also varies somewhat, being more sinuous and the two lobes more obvious in the female and smaller specimens (Fig. 2B, C). In addition, large male specimens have a proportionately wider carapace which is more swollen with the dorsal surface more convex (Fig. 2D) (versus surface relatively lower in smaller ones; Fig. 2E); the posterior margin of epistome has the median lobe more prominent, triangular in shape with a sharp tip (Fig. 2D, F) (versus lower and more rounded in smaller ones; Fig. 2E, G); the anterior thoracic sternum, notably sternites 1–3 appear transversely narrower (Fig. 2H) (versus relatively wider in smaller ones; Fig. 2I); the surfaces of male thoracic sternites 1–4 are distinctly pitted (Fig. 2H) (versus distinctly smoother surface with only scattered pits; Fig. 2I); have a relatively more quadrate male pleon with the lateral margins less divergent (Figs. 2H, 3H) (versus more triangular with lateral margins more divergent in smaller ones, Figs. 2I, 3G).
The diagnostic G1, with the strongly curved subterminal segment and swollen basal part of the terminal segment is constant for large and small specimens (Figs. 4A–D, 5A–D, F–H).
Colour in life. Not known.
Etymology. The name is derived from an arbitrary combination of the name Ngan with the Latin “ anima ” for soul; alluding to the kind and generous person Ngan Kee was. She was a good student, a trusted friend and a wonderful colleague; The author will sorely miss her enduring optimism, calming influence and cheeky smile. The name is used as a noun in apposition.
Remarks. The general carapace features and structure of the G1 of T. nganima n. sp. most closely resemble those of T. annamense (Balss, 1914) (Phuc-Son, Annam). Compared to T. annamense, in T. nganima n. sp., the posterior margin of the epistome has the median lobe clearly defined, projecting anteriorly from the lateral parts, forming sinuous margins (Fig. 2F, G) (versus median lobe low, broadly triangular, with the margin gently contiguous with the lateral parts forming concave margins in T. annamense; Ng & Yeo 2001: fig. 1B); the male pleon is proportionately more quadrate, with somites 3 and 4 relatively narrower (Fig. 3F, G) (versus pleon wider, especially across somites 3 and 4 in T. annamense; Ng & Yeo 2001: fig. 2B); the G1 has the median part of the subterminal segment more strongly curved (Figs. 4A, B, 4A) (versus gently curved in T. annamense; Ng & Yeo 2001: fig. 2F, H); and the outer surface of the basal part of the terminal segment is prominently swollen, even in smaller specimens (Figs. 4C, D, 5A–D, F–H) (versus surface smooth, without any swelling in T. annamense; Ng & Yeo 2001: fig. 2D–I).
The distributions of T. annamense and T. nganima n. sp. are also 650 km apart. Ng & Yeo (2001) re-examined, redescribed and figured the types of T. annamense and selected a lectotype male for the species. They noted that the type locality of the species was “Phuc-Son, Annam (now in northern Vietnam)” (Ng & Yeo 2001: 279). This is not accurate as the type locality “Phuc-Son, Annam ” is actually in central Vietnam. Balss (1914: 406; 1937: 169) described Geothelphusa annamensis on the basis of many specimens collected by the well-known German collector, Hans Fruhstorfer, from Phuc-Son in Annam. No date was given but Balss (1937: 170) referred to an insect catalogue which documented Fruhstorfer’s field work, and this indicates that the material was collected between November and December 1899 (see Fruhstorfer 1905). The name “Phuc-Son” is well known in the older literature on Vietnamese animals and plants. This location was in “ Annam ”, a French protectorate during colonial times, in what is today central Vietnam. “Phuc-Son” is today known as Phýớc Sõn (or Phuoc Son) District, in Quang Nam Province in central Vietnam. This was where the Annamite mountain range is found (today known as Trýong Sõn Mountain, ca. 15.39°N 107.82°E). In describing a second species, Potamon fruhstorferi (at present in Balssipotamon Đăng & Hồ, 2008), Balss (1914: 403) noted that it was collected from “ Annam, Phuc Son, 50 km westlich vom Hafen Touranne”. Touranne is the old name for what is today the city of Da Nang, a municipality at the edge of Quang Nam Province. Phýớc Sõn District is about 50–60 km southwest of Da Nang. This location should not be confused with another two sites also named “Phúc Sõn” in northern Vietnam; one in Tân Yên District, Bac Giang Province (ca. 21.42°N 106.04°E) and another in Anh Sõn District, Nghe An Province (ca. 18.86°N 105.02°E), with both areas in what was called “ Tonkin ” in colonial times.
description: Published as part of Ng, Peter K. L., 2024, Taxonomic notes on three species of Tiwaripotamon Bott, 1970 (Crustacea: Brachyura: Potamidae) from Vietnam and China, one of which is new to science, pp. 298-313 in Zootaxa 5476 (1) on pages 299-305, DOI: 10.11646/zootaxa.5476.1.24, http://zenodo.org/record/12681699