Monday, August 8, 2016

[Ichthyology • 2013] Three New Species of Freshwater Halfbeaks (Teleostei: Zenarchopteridae: Hemirhamphodon) from Borneo; Hemirhamphodon sesamum, H. byssus & H. kecil


Hemirhamphodon sesamumH. byssus & H. kecil
Tan & Lim, 2013


Three new species of Hemirhamphodon are described from Borneo island. Hemirhamphodon sesamum, new species, from lowland basins draining into the Makassar Strait, differs from its congeners in having unique colour markings on its dorsal fin and lower jaw; males with posterior projections on the fourth anal-fin ray, with third, fourth and eighth anal-fin rays branched, and with posterior projections on the fourth anal ray; females with third and fourth anal-fin rays branched. Hemirhamphodon byssus, new species, from southern Sarawak differs from the allopatric H. kuekenthali in having the anterior dorsal-fin ray extensions reaching to the middle of the caudal fin (vs absence or small extensions on dorsal-fin rays), black pigment on the anterior half of dorsal fin (vs middle part of dorsal fin), males with posterior projections on the fourth anal-fin ray. Hemirhamphodon kecil, new species, from the lower Mahakam in East Kalimantan, can be distinguished from its congeners in having few or no markings except for sparse black pigment along sub-margin of the dorsal fin and anterior dorsal margin of the caudal-fin base. It is a small species (up to 41 mm SL). Notes and a figure of the holotype of H. phaiosoma are provided, along with colour descriptions of fresh material. An artificial key to Hemirhamphodon, inclusive of the new species, is also included.

Key words: Hemirhamphodon, Southeast Asia, biodiversity, taxonomy, allopatry

  


Hemirhamphodon sesamum, new species 

Etymology. — The species name refers to the minute oily seeds of the Sesamum plant (Pedaliaceae); in allusion to the small black spots/dashes on the dorsal fin with which resemble black sesame seeds. Used as a noun in apposition.

Distribution. — Hemirhamphodon sesamum is currently known only from South Kalimantan, Indonesian Borneo, in lowland drainages of the Batulicin and Cantung basins that drain eastwards into the Makassar Strait (Fig. 7).


Hemirhamphodon byssus, new species (Figs. 9A–E, 10A, 11A, B)
Dermogenys species undetermined – Doi et al., 2001: 16, Fig. 2 
Hemirhamphodon kuekenthali (non-Steindachner) – Anderson & Collette, 1991 (part); Kottelat & Lim, 1995 (part); Doi et al., 2001; Jongkar & Lim, 2004
Hemirhamphodon pogonognathus (non-Bleeker) – Roberts, 1989 (part)

Etymology. — From the Latin byssus, meaning fine thread, in allusion to the distinct filamentous dorsal-fin rays of large males. Used as a noun in apposition.

Distribution. — Hemirhamphodon byssus is known from the lowland stream systems in southern Sarawak that include Sematan, Lundu, Bau, Batu Kawa, Matang, Bako, Serian, Balai Ringin, Gedong and Sri Aman (Fig. 7). From Sibu northwards (including Bintulu and Baram areas, and Brunei Darussalam), it is replaced by H. kuekenthali with which it is apparently allopatric. This distribution pattern is shared with the following allopatric species pairs (in south–north orientation): Rasbora kalochroma/R. kottelati (Lim, 1995), Betta ibanorum/B. akarensis (Tan & Ng, 2004, 2005).


Hemirhamphodon kecil, new species (Figs. 12A–E, 13A, B) 
Hemirhamphodon pogonognathus (non-Bleeker) – Anderson & Collette, 1991 (part); Christenson, 1992; Kottelat et al., 1993 (part); Kottelat, 1994.

Distribution. — Hemirhamphodon kecil is currently known only from East Kalimantan, Indonesian Borneo, in the waterways of the lower Mahakam basin that drain eastwards into the Makassar Strait (Fig. 7).

Etymology. — From the Bahasa Indonesian word ‘kecil’, meaning small, in reference to the diminutive size of this species. Used as a noun in apposition.



Heok Hui Tan and Kelvin K. P. Lim. 2013. Three New Species of Freshwater Halfbeaks (Teleostei: Zenarchopteridae: Hemirhamphodon) from Borneo.
The Raffles Bulletin of Zoology. 61(2): 735-747.

  

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