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| [upper & A] Trigonostigma truncata ปลาซิวข้างขวานใหญ่ [B] T. heteromorpha ปลาซิวข้างขวาน
Tan, 2020
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Abstract
Trigonostigma truncata, new species, is described from the coastal swamp forests along the east coast of the Malay Peninsula. It differs from all congeners, in having a gently sloping lateral head and nape shape, the characteristic black triangular marking, newly termed here as the axine, which is large with its caudal apex not reaching caudal-fin base, presence of orange-red colour on the anal fin, a bluish-lilac coloured sheen on body in life, and a shallower body depth as compared to its most similar congener, T. heteromorpha. A key to the genus Trigonostigma and a brief redescription of T. heteromorpha is also included.
Key words. new species, biodiversity, Southeast Asia, acid waters, Cypriniformes
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| Fig. 3. Trigonostigma truncata, new species, live specimen of ca. 30 mm SL (trade material, not preserved). |
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| Fig. 4. A, Trigonostigma truncata, new species, ZRC 54736, 33.7 mm SL, trade material; B, T. heteromorpha, ZRC 61239, 28.4 mm SL, trade material; C, T. espei, ZRC uncat, 28.2 mm SL, trade material (obese individual); D, T. hengeli, ZRC uncat, 23.3 mm SL, Sumatra: Jambi; E, T. somphongsi, not preserved, ca. 15 mm SL (right-side reversed; photograph by N. Panitvong). |
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Trigonostigma truncata, new species, live specimen of ca. 30 mm SL (trade material, not preserved).
A, Trigonostigma truncata, new species, ZRC 54736, 33.7 mm SL, trade material;
B, T. heteromorpha, ZRC 61239, 28.4 mm SL, trade material;
C, T. espei, ZRC uncat, 28.2 mm SL, trade material (obese individual);
D, T. hengeli, ZRC uncat, 23.3 mm SL, Sumatra: Jambi;
E, T. somphongsi, not preserved, ca. 15 mm SL (right-side reversed; photograph by N. Panitvong).
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Trigonostigma truncata, new species
ปลาซิวข้างขวานใหญ่
Rasbora heteromorpha (non-Duncker) – Mohsin & Ambak, 1983: 50 (part); Kottelat et al., 1992: 9, table 1; Kottelat et al., 1993: 63, pl. 18 (part).
Rasbora cf. heteromorpha – Collins et al., 2012: 10, table 3, supplementary data table S1: 16 (part?).
Trigonostigma heteromorpha (non-Duncker) – Kottelat & Witte, 1999: 54 (part), fig. 10; Kottelat, 2013: 170 (part); Panitvong, 2020: 142.
Trigonostigma aff. heteromorpha – Ng et al., 2019: 527 (part).
Diagnosis. Trigonostigma truncata, new species, is most similar to T. heteromorpha, in having a large black axine starting from approximately mid-body with dorsal apex near dorsal-fin origin, ventral apex near pelvic-fin origin, and caudal apex near caudal-fin base; this axine being the largest amongst all congeners. Trigonostigma truncata differs from T. heteromorpha in the following characters: a gently sloping lateral head profile to pre-dorsal region (vs. a steep convex lateral profile from posterior of head to predorsal region); sub-superior mouth (vs. terminal mouth); caudal apex of axine not reaching caudal-fin base (vs. reaching and extending to hypural plate); dorsal and ventral apices of axine originate posterior to both dorsal-fin and pelvic-fin origins by up to three scale-widths (vs. dorsal apex starting one scale-width posterior to dorsal-fin origin and ventral apex starting at pelvic-fin origin; see Figs. 4, 5); faint or indistinct brown humeral streak just posterior to opercular opening (vs. a distinct black humeral streak); base of dorsal fin hyaline and its middle reddish-orange in life (vs. anterior two-thirds of fin orange-red); presence of distinct orange-red colour on anal fin in life (vs. faint or absence); having a bluish-lilac sheen on the body in life (vs. reddish or purplish sheen); and having a shallower body (depth at dorsal-fin origin 28.3–34.6% SL [mean 32.4], vs. 32.6–38.2% [mean 35.8]).
Distribution. Trigonostigma truncata, new species, is currently known from the east coast of the Malay Peninsula, from south of the Isthmus of Kra in Narathiwat province of southern Thailand to the Malaysian State of Terengganu (Fig. 6). The map in Fig. 6 also shows the distribution of all five species for comparison.
Field notes. This species is found in lowland freshwater acid swamp-forest stream habitats, usually flowing into riverine habitats. Syntopic species collected from Mae Nam Tod Deng swamp forest in South Thailand include the following: Notopterus notopterus (Notopteridae), Boraras urophthalmoides, Trigonopoma gracile (Danionidae), Kryptopterus minor (Siluridae), Clarias meladerma (Clariidae), Monopterus javanensis (Synbranchidae), Chaudhuria sp. (Chaudhuriidae), Oryzias minutulatus (Adrianichthyidae), Indostomus crocodilus (Indostomidae), Betta imbellis, B. pi, Parosphromenus paludicola, Trichopodus trichopterus, Trichopsis vittata (Osphronemidae), Channa limbata, and C. lucius (Channidae).
Syntopic species collected from Kuala Brang in Terengganu include the following: Osteochilus vittatus (Cyprinidae), Rasbora bankanensis, R. dusonensis, Trigonopoma gracile (Danionidae), Acanthopsoides sp., Lepidocephalichthys furcatus, Pangio cuneovirgata, P. piperata, P. semicincta, P. muraeniformis (Cobitidae), Homalopteroides nebulosus (Balitoridae), Nemacheilus selangoricus (Nemacheilidae), Barbucca diabolica (Barbuccidae), Hemibagrus capitulum, Nanobagrus fuscus, Pseudomystus stenomus (Bagridae), Silurichthys hasseltii (Siluridae), Parakysis verrucosus (Akysidae), Clarias leiacanthus (Clariidae), Neostethus smithi (Phallostethidae), Bihunichthys sp. (Chaudhuriidae), Hemirhamphodon pogonognathus (Zenarchopteridae), Xenentodon canciloides (Belonidae), Doryichthys martensii (Syngnathidae), Brachygobius xanthomelas (Gobiidae), Pristolepis grooti (Pristolepididae), Luciocephalus pulcher, and Parosphomenus paludicola (Osphronemidae).
Syntopic species collected from Dungun swamp in Terengganu include the following: Barbodes cf. binotatus, Desmopuntius hexazona, Osteochilus vittatus, O. waandersii (Cyprinidae), Boraras maculatus, Rasbora einthovenii, R. cephalotaenia, R. paucisqualis, Trigonopoma gracile, T. pauciperforatum (Danionidae), Lepidocephalichthys furcatus, Pangio semicincta (Cobitidae), Homalopteroides nebulosus (Balitoridae), Nemacheilus selangoricus (Nemacheilidae), Neostethus smithi (Phallostethidae), Hemirhamphodon pogonognathus (Zenarchopteridae), Nandus nebulosus (Nandidae), Betta stigmosa, Luciocephalus pulcher, and Parosphromenus paludicola (Osphronemidae).
Etymology. From the Latin ‘truncus’, meaning cut off, in allusion to the caudal apex of the axine not reaching the base of the caudal-fin. Used as a noun in apposition.
Trigonostigma heteromorpha (Duncker, 1904)
Rasbora heteromorpha Duncker, 1904
Distribution. Trigonostigma heteromorpha is the most widely distributed species of the genus, occurring in Malay Peninsula (Perak, Selangor, Negri Sembilan, Johor, Pahang), Singapore, Sumatra (North Sumatra and Riau provinces), Riau archipelago islands of Batam, Bintan, and Lingga, Bangka island and Belitung island (see Fig. 5). In Sumatra, T. heteromorpha is found only in North Sumatra and Riau provinces and is replaced by T. hengeli in Jambi and South Sumatra provinces (Kottelat & Witte, 1999; Tan & Kottelat, 2009).
Tan Heok Hui. 2020. Trigonostigma truncata, A New Species of Harlequin Rasbora from Malay Peninsula (Teleostei: Danionidae). RAFFLES BULLETIN OF ZOOLOGY. 68; 421–433.
