Monday 28 September 2020

NOVATAXA: A New “Beakless” Halfbeak of the Genus Nomorhamphus

[Ichthyology • 2020] Nomorhamphus aenigma • A New “Beakless” Halfbeak of the Genus Nomorhamphus (Teleostei: Zenarchopteridae) from Sulawesi

Nomorhamphus aenigma 
Kobayashi, Masengi & Yamahira, 2020

A new viviparous halfbeak, Nomorhamphus aenigma, new species, from the upper stream of the Cerekang River in central Sulawesi, Indonesia is described. The new species is distinguished from all other zenarchopterids by the complete absence of elongate lower jaws. Although secondary loss of elongate jaws is also known from several hemiramphids, N. aenigma, new species, is clearly different from them by having no elongate jaws throughout ontogeny.

Fig. 2 Photographs of Nomorhamphus aenigma, new species, immediately after fixation.
 (A) MZB 25100, holotype (male, 34.7 mm SL),
(B) MZB 25103, paratype (female, 37.8 mm SL),
(C) NSMT-P 136106, paratype (female, 43.0 mm SL).

Nomorhamphus aenigma, new species
Diagnosis.—Nomorhamphus aenigma is distinguished from all other congeners by the absence of any elongation of the lower jaw throughout ontogeny. Nomorhamphus aenigma is also distinguished from all other congeners by a combination of the short and expanded teeth on gill rakers, 22–23 precaudal and 16–17 caudal vertebrae, 13–14 anal-fin rays, 12 segments in the male first anal-fin ray, and distal tips of the male second and third anal-fin rays having no contact with each other.

Fig. 4 Type locality of Nomorhamphus aenigma, Cerekang River, approximately 600 m downstream from Laroeha Village, Luwu Timur District, Regency of Wasuponda, Sulawesi Selatan. Photo taken 3 September 2019.

Distribution and habitat.—Nomorhamphus aenigma is known from the main stream of Cerekang River in Sulawesi Selatan, Indonesia (Fig. 1). The river belongs to the Malili River basin. The holotype was collected from a locality near Laroeha Village. The type locality (2°27′39.7″S, 121°04′03.0″E) is approximately 10 m in width and 1.5 m in depth, partially shaded by forest canopy, and has mud and gravel as substrates (Fig. 4). Nomorhamphus rex (Fig. 7), Oreochromis niloticusOryzias dopingdopingensisOsteochilus vittatusRedigobius penango, and Telmatherina sp. co-occurred.

Etymology.—The specific name “aenigma,” from ancient Greek noun for “riddle,” refers to the riddle raised by this species: “why are the mandibles of most halfbeaks long?” 

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