Comparative morphology of the urohyal bone between two species of the genus Tlaloc (Actinopterygii, Cyprinodontiformes, Profundulidae)
2025
Alejandro Padilla-Sánchez | Sara E. Domínguez-Cisneros | Ernesto Velázquez-Velázquez | Abraham Kobelkowsky
The genus Tlaloc contains four valid species and forms part of the family Profundulidae, a group of small freshwater fishes endemic to the Mesoamerican region. The objective of this study was to provide a detailed description of the urohyal bone of two species of Tlaloc—Tlaloc labialis (Günther, 1866) and T. candalarius (Hubbs, 1924)—and to evaluate the usefulness of this osteological structure in delimiting these taxa. The urohyal bone is a single bony structure located in the ventral part of the head in both species and is the result of ossification of an unpaired tendon of the sternohyoideus muscle. Data from cleared and double-stained museum specimens of the focal taxa were analyzed, including morphometric measurements of each urohyal bone taken using an ocular micrometer connected to a stereomicroscope. We found the most notable difference between the two species was the height of the urohyal neck, which was significantly narrower in T. candalarius (6.66%–11.11% of total urohyal length) than in T. labialis (13.15%–25%) based on the non-parametric Mann–Whitney U test. Our results show that measuring the urohyal bone offers a reliable and attractive alternative for taxonomic determination of Tlaloc labialis vs. T. candalarius due to the operational simplicity and speed of such measures. Our work also highlights the utility of more detailed osteological analyses in taxonomic and systematic studies of profundulids.
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