[1] They are common inhabitants of coral reefs and rocky habitats along the eastern Pacific Ocean coasts of Mexico, the United States, and Canada, although they are hardly noticed, as they often rest motionless near their shelters.

[4] In 1960, James E. Böhlke and C. Richard Robins synonymized Rhinogobiops with the genus Coryphopterus, though they noted that it differed from other members of the latter in the number of fin rays and scales and should be treated as a subgenus.

He was supported by ichthyologists Ray S. Birdsong and even Robins himself in believing that Rhinogobiops is in fact distinct from Coryphopterus.

They concluded that blackeye gobies were more closely related to a clade containing Lophogobius cyprinoides than to the rest of the genus.

[7] Abundant otolith fossils of blackeye gobies from the Pliocene epoch (5.3 to 3.6 million years ago) have been found in Lomita Marl.

The head lacks scales and is wider than it is deep, with a small terminal mouth and a projecting lower jaw.

Below the eye is an iridescent bluish spot clearly visible if illuminated (the source of their other common name – bluespot goby).

The first dorsal fin has a distinctive black upper anterior edge that is retained even when the fish changes color.

[8][13] Blackeye gobies are found in the eastern North Pacific, along the coasts of Canada, the United States, and Mexico.

[15] Its northern range was previously believed to have reached only as far as Skidegate Channel in the Haida Gwaii Archipelago and the waters around Wales Island, both in British Columbia.

Subsequent observations on the recovered specimens in aquaria noted that blackeye gobies could only survive in temperatures exceeding 4 °C (39 °F), making them unlikely to be found further north than St. John Baptist Bay.

They usually seek out natural crevices and holes in the rock and reef surfaces but are capable of digging their own burrows in softer substrates if needed.

They are protogynous hermaphrodites, with all individuals being born females and turning into males once they reach a certain size under the correct conditions.

During breeding season, the size of the territorial range can decrease even further as males concentrate on closely guarding the nests instead of foraging.

When two males meet, they approach each other, slowly undulating their bodies, and assume combat-threat display with all fins stiffly outstretched.

[8] Blackeye gobies are sexually dimorphic, with different sexes distinguishable from genital papilla, size, and length of dorsal and anal fins.

[10][11] They then entice females into the nesting site by swimming up for 2 ft (0.61 m) or more with mouths open and fins outstretched then back down again.

Interested females directly approach the males and slowly undulate their bodies while opening their mouths widely and spreading their fins.

[23] Blackeye gobies are protogynous hermaphrodites – all of them are born females but can shift once to become males once they reach a length of 2 to 3 in (5.1 to 7.6 cm).

The most common prey include amphipods, copepods, isopods, decapods (particularly hermit crabs), snails, and clams.

Parts of echinoderms (mostly sea urchins) and bryozoans are also found in the contents of the stomachs of blackeye gobies, though this is likely the result of incidental ingestion rather than true predation.

Occasionally, they may feed by taking a mouthful of substrate, spitting it out, then picking off edible prey as it drifts to the bottom.

[10][17][22][25] Sea urchins of the genus Strongylocentrotus are also known to dislodge blackeye gobies from their territories, possibly as a result of egg predation by the former.