Xenomystax, Gilbert, 1891

Lin, Chien-Hsiang, Brzobohatý, Rostislav, Nolf, Dirk & Girone, Angela, 2017, Tortonian teleost otoliths from northern Italy: taxonomic synthesis and stratigraphic significance, European Journal of Taxonomy 322, pp. 1-44 : 13

Xenomystax sp.

A massive, thick otolith is referred to the genus Xenomystax Gilbert, 1891 ( Fig. 2C ). The specimen is elliptic and elongate with nearly smooth margins. It is characterised by a rather pointed and extended anterior end and a rounded and robust posterior part. A well-marked and deep dorsal depression on the high dorsal area is observed. The sulcus is wide, oval and situated at the center of the otolith. Otoliths of three Recent species of Xenomystax are illustrated ( Fig. 3 A–D, M–O) for comparison. The fossil specimen is most similar to that of X. congroides Smith & Kanazawa, 1989 ( Fig. 3 M–N), a western Atlantic species, but differs in showing a shallower and more elongate outline and a more extended anterior part.

Figures

Fig. 2. Tortonian fish otoliths from northern Italy. A. Pterothrissus umbonatus (Koken, 1884), Montegibbio (IRSNB P 9855). B. Paraconger sp., Torrente Stirone (IRSNB P 9856). C. Xenomystax sp., Torrente Stirone (IRSNB P 9857). D. Conger conger (Linnaeus, 1758), Torrente Stirone (IRSNB P 9858). E. Argentina sp., Torrente Stirone (IRSNB P 9859). F. Rhynchoconger pantanellii (Bassoli & Schubert, 1906), Torrente Stirone (IRSNB P 9860). G–I. Bathycongrus nagymarosyi (Nolf & Brzobohatý, 1994), Torrente Stirone (IRSNB P 9699–P 9701). J–K. Gnathophis mystax (Delaroche, 1809), Torrente Stirone (IRSNB P 9702–P 9703). L–M. Nansenia sp., Mondovi, Madonna della Neve (IRSNB P 9704–P 9705). N–P. Xenodermichthys senesi Nolf & Brzobohatý, 1994, Mondovi, Madonna della Neve (IRSNB P 9706–P 9708). 1 = ventral view; 2 = inner view. Scale bars = 1 mm.

Fig. 3. A–D, M–O. Recent otoliths of species of Xenomystax Gilbert, 1891. A–D. X. atrarius Gilbert, 1891 from Peru, fish total length (TL) 81 cm, 72 cm, 57 cm and 43 cm, respectively. M–N. X. congroides Smith & Kanazawa, 1989, from off Mississippi. O. X. bidentatus (Reid, 1940), from the Caribbean Sea, TL 48 cm. – E–L. Fossil otoliths of Gadomus tejkali (Brzobohatý & Schultz, 1978) (IRSNB P 9847–P 9854) growth series from Roddi (E) and Mondovi, Madonna della Neve (F–L). 1 = ventral view; 2 = inner view. Scale bars = 1 mm.