The genus Hassar (Doradidae) is a monophyletic group of Neotropical Siluriformes. The
present paper is a taxonomic revision of the species of Hassar, with an osteological
description of type-species H. orestis. This study was based on the survey and analysis of
morphological, morphometric, meristic and color pattern characters for the recognition of
the valid species and consequent diagnosis and redescriptions. The specimens analyzed
(n=727), from domestic and foreign institutions, included individuals preserved in
alcohol, prepared as dry skeletons, cleared and stained, x-rayed and/or photographed. The
specimens were observed directly or with a stereomicroscope and camera lucida.
Measures were made, preferentially, on the left side. The osteological description of
Hassar orestis was based on the analysis of 23 specimens and divided into functional
osteological groups namely: neurocranium, mandibular arch, hyoid arch, branchial
arches, axial skeleton, nucal plates and dorsal fin, laterosensory system and appendicular
skeleton. The results show Hassar as being composed by two species: H. orestis and H.
affinis. Hassar orestis has H. ucayalensis as synonym. Hassar affinis has H. wilderi, H.
iheringi and H. woodi as synonyms. Hassar orestis and H. affinis differ from each other
by the position of the first medial thorn (at the infranucal scute or between the 1st and 8th
lateral scute vs. between the 9th and 16th lateral scute), by the number of lateral scutes
with a medial thorn (24 to 33 vs. 18 to 23 respectively) and by the condition filiform
marginal diverticula of the swimbladder (distinctly larger vs. reduced or absent
respectively). The adults (>14 cm) of H. orestis and H. affinis are distinguished by of the
depth caudal peduncle (4.11-5.71% SL vs. 5.73 -7.63% SL respectively) and by the size
of the adipose eyelid (conspicuous and elongate over the anterior border of the eyes vs.
tenuous over the anterior border of the eyes respectively). No morphological,
morphometric and meristic differences among juveniles and adults of the same species
were found. Both species present the same color pattern and share a subterminal black
spot on the first rays of the dorsal fin, but some specimens of H. affinis present a terminal
black spot. The presence of a cartilaginous extension on prolongation in the first ray of
the dorsal fin, in some males of H. orestis, confirmed the notion of sexual dimorphism for
this species. Specimens of H. orestis from the Amazon, Solimões, and Negro rivers differ
from the population from the Branco river and from the Essequibo and Orinoco basins by
the presence or absence of thorns on the tympanic scutes and on the infranucal scute. No
differences were found between the swimbladders of those populations. The distribution
of H. affinis was extended for the rivers Solimões, Tapajós, upper and lower Xingu,
Tocantins, Araguaia, Parnaíba and Pindaré-Mearim System. Hassar affinis and H. orestis
have a wide, partially disjunct distribution, with an area of sympatry. The osteological
description of the H. orestis provides a better anatomical understanding of the group, and
basic data for future on anatomy, ontogeny, ecomorphology and systematics and
taxonomy.
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