A tiny goby endemic to the archipelago, sitting on rock faces and in crevices.
To 2.5 cm, and one of the smallest fish on this site. The upper half of the head is red and the lower half whitish with red spots, with four narrow blue bars across the top of the head, and the body runs red at the front to purplish brown at the rear with thirteen to fifteen narrow blue bars along it. There is a fleshy crest along the top of the head and nape and the mouth is set very obliquely. No other Lythrypnus is recorded from these islands, so in practice there is nothing here to confuse it with. Against the bluebanded goby, which divers know from California and the Gulf, the separator is the bar count: thirteen to fifteen against three to five.
Rock faces and crevices from three to twenty metres, on the bottom. It feeds on zooplankton and small crustaceans taken off the rock. It is recorded from the Revillagigedo Islands and nowhere else. Beyond that very little is published: no behaviour has been described for it, and the two databases disagree on its conservation status, STRI listing it as Vulnerable and FishBase as Least Concern on a 2024 assessment.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.
