Akrokolioplax, E Zhang & Maurice Kottelat, 2006

E Zhang & Maurice Kottelat, 2006, Akrokolioplax, a new genus of Southeast Asian labeonine fishes (Teleostei: Cyprinidae)., Zootaxa 1225, pp. 21-30 : 23-24

Akrokolioplax , new genus

Type species: Epalzeorhynchos bicornis Wu, 1977 .

Diagnosis

Akrokolioplax belongs to the tribe Labeonini (sensu Reid, 1982), which is diagnosed by the following four unique characters: (1) presence of a vomero-palatine organ; (2) neural complex of Weberian apparatus in direct contact with the supraoccipital region of the skull; (3) basioccipital with a terete process; (4) lower lip developed posterior to lower jaw. Akrokolioplax shares with Epalzeorhynchos what has usually been called “rostral lateral lobes” (e.g. Smith, 1945), but these “lobes” actually are not homologous in the two genera because they differ in their position and structure (see below). Akrokolioplax is further distinguished from Epalzeorhynchos in having the upper lip absent or vestigial (vs. present, medially reduced and separated from the upper jaw), the upper jaw completely covered by the rostral fold (vs. not covered medially) and laterally connected (vs. disconnected) by a frenum with the lower lip around the corner of the mouth, the lower lip with an exteriorly papillose (vs. smooth) anterior margin, and maxillary barbels tiny (vs. well-developed).

As the “lobes” of Epalzeorhynchos and Akrokolioplax are not homologous structures, we will use the term “rostral lobe” only for Epalzeorhynchos , as it has long been used in the literature (e.g. Weber & de Beaufort, 1916; Smith, 1945), and the term ‘rostral flap’ for Akrokolioplax . In Epalzeorhynchos (Fig. 2A), the lobe is an elongate conical structure, with a conspicuous conical tubercle at its tip (already present in specimens 33.3-56.6 mm SL) and a series of conical and starry tubercles along its lower edge. It is encased in a widened sublachrymal groove (which borders the rostral fold) and surrounds the rostral barbel. The lobe is movable, and can rotate upwards along a more or less longitudinal axis to reach a position above the sublachrymal groove. The infraorbital branch of the cephalic lateral-line system ends anteriorly along the upper edge of the sublachrymal groove, the anterior pore being located nearly opposite to the mid-length of the rostral lobe.

In Akrokolioplax (Fig. 2B), the flaps are broadly rounded, triangular, paired structures at the tip of the snout. The flap is fleshy, with a relatively sharp (but not cutting) edge, located in a depression close to the tip of the snout. It is movable forward along a vertical axis. The flap has a number of small conical tubercles along its lower edge. In our smallest specimens (106.2 mm SL), the depression under and around the flap is continued ventrally as a semi-circular groove, which in turn is connected to the sublachrymal groove in front of the rostral barbel. The sublachrymal groove passes along the rostral barbel, but does not surround it anteriorly, or the rostral barbel is in the sublachrymal groove. In larger specimens (122.4 mm SL), the semi-circular groove is missing. The infraorbital branch of the cephalic lateral-line system ends anteriorly along the edge of the sublachrymal groove, with the anterior pore positioned slightly in front of the base of the rostral barbel, at some distance below the rostral flap. Yang and Winterbottom (1998: fig. A5c) figured the lachrymal with a slight concavity at the anterior extremity of their 101 mm SL C&S specimen. In our 122.0 mm SL C&S mm SL specimen, there is a marked concavity in the same location, possibly corresponding to the depression in which the flap is located.

Etymology

Derived from a combination of the Greek akrokolion, the extremities of the body, especially of animals (snout, ears, or trotters); and plax, flat and broad, in allusion to the presence of a pair of fleshy rostral flap on the tip of the snout. Gender: feminine.