The saddleback gunnel was first formally described as Gunnellus ornatus in 1854 by the French biologist Charles Frédéric Girard with the type locality given as Presidio, San Francisco, California.

[3] The specific name ornata means "decorated" or "adorned", assumed to be an allusion to the 12–13 blackish-brown saddle markings on back, as well as the light and dark streaks which radiate outwards from the eyes.

[4] The head's lateral system functions using a series of pores, including "two nasal, six suborbital, six postorbital, three occipital, four mandibular, and five preopercular.

The dorsal fin has short, thick spines and is significantly long, on average reaching 86.2% of the fish's body length.

Its thermal capacity aids in its ability to adapt to the changing environments and seasonal plants every summer.

Additionally, P. ornata's diet consists of mid-sized Macoma siphons and tanids and large gammarid amphipods.

It is observed that saddleback gunnel's stomachs are fuller in the midmorning, rather than at night, suggesting the fish tend to consume prey in the morning.

Young saddleback gunnel tends to live in eelgrass, where harpacticoid is widely available for consumption.

[11] Eelgrass beds and other vegetative coastal habitats are the most vulnerable by human activities among all marine ecosystems.

[12] The saddleback gunnel ranges from Vancouver Island in the north to Santa Barbara County, California in the south.

Saddleback gunnel also appears to have Canadian populations migrating to these areas during the cold winter months.

[6] Pholis ornata are commonly found in estuaries on the west coast of the U.S., including in the northeast Pacific West coast, and Yaquina Bay, Oregon, sharing community with other marine fishes that line near the shore such as the Pacific staghorn sculpin and rockfishes.

In these estuaries, eelgrass beds are an important feature in Pholis ornata's habitat, acting as nurseries and living areas for the fish.

Additionally, seasonal patterns were observed to impact the Pholis ornata's population numbers in Yaquina Bay throughout the year.

Population density is higher in late winter to early spring due to increased post-larval individuals inhabiting rocky intertidal areas.

Pholis ornata are also observed to eagerly inhabit and hide in seasonally available plants that act as cover for the fish.

[14] Pholis ornata are also an important part of the ecosystem in Puget Sound, a culturally and economically body of water in the Pacific Northwest.

[6] Pholis ornata, along with other fish species in this area, can be used as researchers and fishermen as an indicator of a healthy and diverse ecosystem.

Healthy eelgrass meadows with diverse fish populations, including P. ornata, are beneficial to nearshore-ecosystem health and commercial fisheries.