Sunday, February 23, 2020

[Ichthyology • 2020] Ammoglanis obliquus • A New Psammophilic Species of the Catfish Genus Ammoglanis (Siluriformes, Trichomycteridae) from the Amazon River Basin, northern Brazil

Ammoglanis obliquus 
Henschel, Bragança, Rangel-Pereira & Costa, 2020

Ammoglanis obliquus sp. nov., a minute catfish species reaching a maximum adult size of 15.5 mm, is described from the Rio Preto da Eva drainage in the central Brazilian Amazon. It is distinguished from all of its congeners in possessing an exclusive combination of character states, including the presence and number of premaxillary and dentary teeth, number of interopercular and opercular odontodes, presence of cranial fontanel, number of dorsal-fin rays, number of anal-fin rays, number of caudal-fin rays, number of pelvic-fin rays, number of pectoral-fin rays, absence of pelvic splint, antorbital morphology, and absence of supraorbital and autopalatine morphology. It is considered to be a member of a clade also including A. pulex and A. amapaensis due to the unique oral, antorbital, and autopalatine morphology. Ammoglanis obliquus is regarded as more closely related to A. pulex than to any other congener, as both species exhibit a similar colour pattern, an absence of the metapterygoid, and the presence of two finger-like projections on the chin region.

Key Words: Taxonomy, tropical rain forest, Sarcoglanidinae, systematics

Figure 2. Live specimen of Ammoglanis obliquus: UFRJ 12448; 13.0 mm SL.

Figure 1. Ammoglanis obliquus: UFRJ 12477, 14.1 mm SL (holotype): Amazonas river basin. A. Lateral left view; B. Dorsal view.

Ammoglanis obliquus sp. nov.

Diagnosis: Ammoglanis obliquus differs from all its congeners except A. pulex by the presence of seven diagonal rows of dark cromatophores forming a banded pattern on flank of live specimens (vs trunk with three longitudinal rows of dark chromatophores in A. diaphanus and A. amapaensis, or whitish with few minute dark chromatophores scattered on body in A. multidentatus), the absence of metapterygoid (Fig. 3; vs presence), and by the presence of two finger-like projections on chin region (de Pinna and Winemiller 2000: fig. 2b; vs absence). It is distinguished from A. pulex by the presence of dentary teeth (Fig. 4A; vs absence), the presence of premaxillary teeth (Fig. 4B; vs absence), by having 6+6 caudal-fin rays (vs 5+5), and by the absence of the pelvic splint (vs presence). It further differs from A. diaphanus, A. amapaensis, and A. multidentatus by the absence of the sesamoid supraorbital (Fig. 5, vs presence), by having fewer premaxillary teeth (3 vs 9–12 in A. diaphanus, 8–11 in A. amapaensis, and 10 or 11 in A. multidentatus), fewer dentary teeth (4 vs 8 in A. diaphanus, 7 or 8 in A. amapaensis, and 11–13 in A. multidentatus), and fewer dorsal-fin rays (total of 8 vs 10 in A. diaphanus, 9 in A. amapaensis, and A. multidentatus). It is distinguished from A. diaphanus and A. multidentatus by the presence of 6 pectoral-fin rays (vs 7 in A. diaphanus and 7 or 8 in A. multidentatus), and the presence of a scythe-shaped antorbital (vs antorbital straight, with its tip not curved mesially); from A. amapaensis, by the presence of a wide cranial fontanel (vs dorsal surface of the neurocranium totally ossified, without a fontanel; Mattos et al. 2008: fig. 4), absence of separate ossification of the anterior cartilage of autopalatine (vs presence); from A. multidentatus, by possessing fewer opercular odontodes (8–11 vs 15 or 16), fewer interopercular odontodes (5–8 vs 10 or 11), fewer anal-fin rays (total of 8 vs 9), and fewer pelvic-fin rays (total of 4 or 5 vs 6).

Distribution: Known only from its type locality in Rio Preto da Eva drainage, Amazonas river basin, northern Brazil.

Etymology: From the Latin obliquus, meaning oblique, referring to the conspicuous diagonal banded colouration pattern of living specimens.

Ecological notes: This species is known only from a small clearwater tributary of Preto da Eva river, which is a left margin tributary of the Amazonas river. Individuals were found associated with a sand-bank lying on the centre of an artificial widening of the main course, next to a road. The stream course margins were lined by gallery rainforest, and the water column was about 1 m deep with a weak current. The sand-bank was composed of coarse, yellow sand and with sparse patches of small banks of macrophytes. Capture was accomplished by scooping of the superficial layer of sand with fine hand-nets. Specimens of Potamoglanis Henschel, Mattos, Katz & Costa, 2018 and Ammocryptocharax Weitzman & Kanazawa, 1976 were frequently captured together with Ammoglanis obliquus. This area as a whole is under high deforestation pressure due to local human occupation.

 Elisabeth Henschel, Pedro H. N. Bragança, Filipe Rangel-Pereira and Wilson J. E. M. Costa. 2020. A New Psammophilic Species of the Ccatfish Genus Ammoglanis (Siluriformes, Trichomycteridae) from the Amazon River Basin, northern Brazil.  Zoosystematics and Evolution. 96(1): 67-72. DOI: 10.3897/zse.96.48952