Xenisthmus

Gill, Anthony C., Bogorodsky, Sergey V. & Mal, Ahmad O., 2017, Review of Red Sea Xenisthmus Snyder (Teleostei: Gobioidei: Xenisthmidae), with description of a new species, Zootaxa 4286 (2), pp. 203-214 : 204

Key to species of Xenisthmus in the Red Sea

1 Tongue rounded to truncate; posterior nostril with well-developed anterior flap; second dorsal-fin rays I,11–12, usually I,11; anal-fin rays I,10–11; ctenoid scales extend anteriorly on midside to below origin of second dorsal fin in specimens larger than about 15 mm SL (ctenoid scales mostly restricted to caudal peduncle in smaller specimens)................ X. polyzonatus

- Tongue indented; posterior nostril with raised rim, but without well-developed anterior flap; second dorsal-fin rays I,13–15; anal-fin rays I,12–14; ctenoid scales restricted to caudal peduncle or absent........................................2

2 Five preopercular pores (pores MNOPQ); second dorsal-fin rays I,13–14, usually I,13; anal-fin rays I,12–13, usually I,12.................................................................................................. X. balius

- Three preopercular pores (pores MNO); second dorsal-fin rays I,14–15, usually I,15; anal-fin rays I,13–14................................................................................................ X. oligoporus new species