These organisms are typically distinguished by their eel-like morphology and, in certain species, facial features that evoke an appearance of "pouting".

This species was discovered at Jacó Scar, hydrothermal seep site in the Pacific Ocean.

[2] Pyrolycus jaco is a newly discovered species found in the Eastern Pacific Ocean off the coast of Costa Rica.

This species is the fourth member of the Zoaridae family associated with the deep sea hydrothermal and methane sites in the eastern Pacific to be discovered following Thermacres andersoni and T. cerberus, Rosenblatt & Cohen 1986, and Pachycara rimae, Anderson 1989 (Frable 2023).

The pectoral fin has between fourteen and fifteen rays within them and sixteen to seventeen gill rakers.

The Zoarcidae family is commonly referred to as eelpouts, a group containing almost 60 genera and nearly 300 species, though not true eels like those in the order Anguilliformes (Frickle 2023).

It is extremely rare for families of fishes to adapt to live in places like hydrothermal vents and methane seeps.

This habitat ranges from 1,604 to 1,854 meters in depth, measures at about five degrees Celsius and contains plants and animals typically found near vents.

[5] This may be caused by less energy being available for molecular repair due to high growth rates to avoid predatory and oxidative stressors.

Due to the precise location and lifestyle of Pyrolycus jaco, individuals of this species, possibly including this genus, are likely to be minimized in size compared to other zoarcids, accompanied with reduction or absence of scales and fins, a simplified skeleton, and coloration differences.

Another type of Eelpout in family Zoarcidae is the Lycenchelys sarsi which lays about twenty to forty large (up to 5.4mm in diameter) eggs buried under the sediment found in their habitats.

Their large eggs that hatch benthic larvae that are not widely dispersed are likely a prominent factor in the species' extreme endemism to hydrothermal vents and methane seeps.

[8] By living in or near hydrothermal vents, leading to colder ambient temperatures, this causes an evolutionary change that slows their developmental rates.

The only known behavior of Pyrolycus jaco is that they are commonly found living among tubeworms in the Jacó Scar hydrothermal seep.

One species within the family relies on algae that is drifting to provide shelter and food resources.

Eelpouts in the Baltic and North seas are being used as key indicator organisms to determine the environmental health of the surrounding area.

Other members within the family are not a good comparison because they are more well-known and common so they could have a different conservation status.