| Abstract | Opsanus phobetron is described from the Bahamas and Cuba, and compared with other members of the genus. It was observed to nest in late December at Bimini. Its black mouth functions as a warning mechanism and is indicated to be of social significance under low albedo conditions. Since the spawning threshold temperature of Opsanus parallels the minimal thermal tolerance of reef corals, Opsanus is considered an "indicator" of temperature coastal waters. Owing to thermal requirements and tolerances it survives as a glacial relict in a few West Indian localities. During the last glacial period the northern distributional limit for the genus may have been as far south as southern Florida. Paleotemperature measurements indicate the "tropical" Atlantic and Caribbean regions were not tropical during the last glacial period; the trans-Florida faunal province, now absent from southern Florida, was continuous around the southern tip of the Florida land mass; reef corals were absent from most of the West Indies; the shore fauna was predominantly temperate in the north and predominantly subtropical in the south. It is improbable that the Florida peninsula neck was submerged during Pleistocene interglacial periods. The Gulf of Mexico disjunct trans-Florida populations are interpreted as glacial rather than interglacial relicts, and a comparison is drawn between the Gulf of Mexico and the Sea of Okhotsk. || ABSTRACT AUTHORS: V. Walters
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