Subterranean Fishes of the World

6034

2022

Ichthyological Exploration of Freshwaters

243-256

31

We studied in detail the head and shoulder girdle skeleton and vertebral column of the holotype of the Mexican endemic swamp eel Ophisternon infernale. This exclusively subterranean species lives in waters inside lime stone caves in Yucatán. Its skeleton shows a number of putative plesiomorphic characters in relation to those of Ophichthys, Rakthamichthys and Typhlosynbranchus: I. In Ophisternon infernale, the basisphenoid is present and well developed. II. In Ophisternon infernale, the dermal shoulder girdle is complete and the posttemporal articulates with the skull. III. In Ophisternon infernale, the basibranchial series is complete and includes basibranchials 1-3. IV. In Ophisternon infernale, the hypobranchials and ceratobranchials are in a typical position with hypobranchials articulating with their respective ceratobranchials. V. In Ophisternon infernale, hypobranchials 2 do not articulate with each other in the midline, but are separated by basibranchials 2 and 3. VI. In Ophisternon infernale, the urohyal is narrow and elongated reaching from the basihyal-hypohyal articulation to the anterior tip of basibranchial 3. VII. Ophisternon infernale has a complete set of upper gill arches comprising epibranchials 1-4, an interarcual bone, pharyngobranchials 2 and 3, upper pharyngeal toothplate 4 and with epibranchials 3 and 4 articulating with each other via uncinate processes.

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