Monday, November 28, 2022

[Ichthyology • 2022] Nemacheilus cacao • A New Species of Loach (Cypriniformes: Nemacheilidae) from the middle Mekong Basin in Laos

Nemacheilus cacao
Bohlen, Kottelat & Šlechtová, 2022


 Nemacheilus cacao, new species, is described from the middle Mekong basin in Laos. It differs from all other species of Nemacheilus by having an incomplete lateral line; and adult males having a plain grey-brown body and head (except ventral side), and with extensive tuberculation on the flank, on the dorsal side of the pectoral fin and on the head and nape. The phylogenetic position of N. cacao in the Selangoricus clade of Nemacheilus, as a sister species to N. platiceps, is supported by the presence of bars on the body in juveniles and females as well as by genetic data.

 Key words. Cobitoidea, taxonomy, Khammouan, Nam Thorn, Xe Bangfai 

Live specimen of Nemacheilus cacao, new species, ZRC 62554, paratype, male, 61.5 mm SL;
 Laos: Khamouane province: Thakkhet district: small tributary of Nam Thorn at cave Tham Nang Eng
(Photo: J. Kühne).

Nemacheilus cacao, new species,
ZRC 62554, paratype, male, 61.5 mm SL.
ZRC 62553, holotype, 56.9 mm SL: mouth in ventral view, 
left suborbital flap in lateral view.

Nemacheilus cacao
, new species

Diagnosis. Nemacheilus cacao is distinguished from all other species of the genus except N. platiceps in having an incomplete lateral line reaching between verticals of pelvicfin origin and of anus, with 33–49 pores (vs. complete). Nemacheilus cacao is most easily distinguished from N. platiceps by its colour pattern, with a uniform dark brown body in adult males. In contrast, N. platiceps has 12–16 narrow bars on the flank, clearly distinct at all sizes and both sexes. In addition, N. cacao is distinguished from N. platiceps by males having: a conspicuous suborbital flap (vs. poorly developed); dorsal surface of first 3–7 pectoral-fin rays covered by densely-set small tubercles; flank with a patch of scales each with a small tubercle (vs. absence of tubercles on pectoral fin and flanks).

Etymology. From Theobroma cacao, the cacao tree whose seeds are used to produce chocolate; itself derived from kakawa in some ancient Mesoamerican language (Kaufman & Justeson, 2007). A reference to the chocolate brown colour of large males. A noun in apposition, indeclinable

Jörg Bohlen, Maurice Kottelat and Vendula Šlechtová. 2022. Nemacheilus cacao, A New Species of Loach (Teleostei: Nemacheilidae) from the middle Mekong Basin in Laos. RAFFLES BULLETIN OF ZOOLOGY. 70511–518.