A new cave-dwelling species of Trimma (Teleostei, Gobiidae) from the Red Sea, with notes on Red Sea endemism in Trimma spp.

A new species of the gobiid genus <i>Trimma</i> is described from the Farasan Banks in the southeastern Red Sea. The new species is characterized by having a predorsal midline with 7-8 scales, the fifth pelvic-fin ray unbranched, cheek and opercle scaleless, all pectoral-fin rays unbranched, and a dorsal fin VI + I,7, without elongate spines. In life, the species is bright yellow throughout, with a distinctive yellow-green longitudinal band in the central third of the dorsal fins. The new species inhabits caves on exposed offshore reefs at depths between 15 and 30 m where it occurs in small groups of up to 10 individuals. The new species appears to be sister to <i>T. winchi</i> from the western Indian Ocean. We also present a multilocus phylogeny (COI, 16S, Ptr, S7I1), including all known Red Sea <i>Trimma</i> and 21 non-Red Sea species, and an expanded supermatrix tree with 93 species to place Red Sea endemism in broader context. This brings the total number of <i>Trimma</i> species known from the Red Sea to 10, with eight appearing to be endemic to the region. The high proportion of endemism in the genus is noteworthy, even for the Red Sea, which has one of the highest proportions of endemic reef fishes in the Indo-Pacific. Moreover, K2P distances in the two widespread species suggest they may also represent cryptic endemic species, but further analyses are needed. The new species is currently known only from the Farasan Banks region despite extensive sampling along the Saudi Arabian Red Sea coast.