Halichoeres sanchezi

H. sanchezi has a fusiform body shape, with large TP males being around 120 mm in size, while juveniles and IP fish range from 30-50 mm. The dorsal fin runs from just behind the head to right before the caudal peduncle with 9 spines and 12 rays. Pectoral fins are fan-shaped with 13 rays, and the pelvic fins are thoracic, 1 spine and 5 rays. The anal fin begins at the midsection of the fish; the 3 spines and 12 rays are of similar size to those of the dorsal fin. Finally, the caudal fin has 12 rays with the central 4 being segmented. Fin rays are an important way to distinguish one species from another, especially in species-rich families such as Labridae, where it can be difficult to tell close relatives from one another. Their mouths are small and terminal, with two enlarged pairs of canines on the upper and lower jaws, followed by a row of 10-15 caniniform/conical teeth. Eyes are medium-sized, 5.5 mm. Their gill rakers are short, as they do not need the longer gill rakers found in filter-feeding fish. They have thin, cycloid scales, but not on the head, save for some irregular patches of scales where the head meets the body. Juveniles and IP fish tend to be more brightly colored and patterned, becoming muted if they transition to TP males. Initial phase fish are a bright orange color dorsally with a gray ventral side. …

H. sanchezi is an endemic species found only in the Revillagigedo Archipelago, four volcanic islands off the coast of Mexico in the tropical eastern Pacific Ocean. The four islands are Roca Partida, Socorro, Clarion, and San Benedicto, with the latter being where samples were collected to identify H. sanchezi as a new species. However, pictures taken by Kreg Martin on Socorro Island in 2013 were retroactively identified as H. sanchezi, so they may not be exclusive to San Benedicto. H. sanchezi was only seen at one site on San Benedicto Island during its discovery, a relatively flat, rocky plain south of the island. The site is around 21-22 meters deep with volcanic rock of varying sizes on the floor. Most of the rock is dark in color, with some patches of white rock. Juvenile H. sanchezi stayed close to the bottom, but bigger IP and terminal phase (TP) individuals were found higher in the water. Both groups were observed near boulders of the volcanic rock, which could provide protection if a predator approached.

H. sanchezi are hermaphrodites, most often protogynous. The largest female in a given area can change its sex to male in order to reproduce with other, smaller females. Additionally, the Halichoeres genus is monandric, meaning all individuals are born female, the only males are those that have transitioned. An initial phase wrasse is female, having not yet gone through any transition, but a terminal phase wrasse is a dominant male, having transitioned from female. This hermaphrodite lifestyle ensures there are always available males to breed with females, aiding in the overall reproductive success of the population. While the most common transition is from female to male, some research on other Halichoeres species has shown that a detransition of a TP male back to being female is possible if a larger male enters the territory. This could be because it is better for the TP male to revert to being female rather than try to fight the new male for the territory. While H. sanchezi development has not been studied due to the remote nature of their habitat and recent discovery, they likely develop similarly to other wrasses. Juveniles mature into adult IP fish, keeping their coloration and general proportions. Only some wrasse become terminal phase adults, these are the territory-holding males. …