Round Sand Eel, Bascanichthys cylindricus

Round Sand Eel, Bascanichthys cylindricus. Underwater photographs taken in Zihuantanejo Bay, Guerrero, February 2026. Photographs courtesy of Ron Woheau, Zihuantanejo. Productive discussions with Dr. Benjamin Victor, Coralreeffish.com noted and greatly appreciated.

The Round Sand Eel, Bascanichthys cylindricus, is a member of the Snake Eel or Ophichthidae Family, and is known in Mexico as tieso redondo. Globally, there are seventeen species in the Bascanichthys Genus, of which five are found in Mexican waters, two in the Atlantic and three in the Pacific Ocean.

The Round Sand Eel has an elongated slender cylindrical body with a rounded cross section. They are brown dorsally transitioning to tan ventrally and the head has subtle pale streaking. They have a relatively short blunt snout with a prominent nostril extending from the upper jaw and the mouth equipped with small conical teeth set in one row on the jaws and two rows on the roof of the mouth and a crescent shaped gill cover. The anal and dorsal fins are set low on the body with the dorsal fin origin being on the head before the gill openings. Their pectoral fins a small flap behind the gill openings. They have a relatively short tail that is 43 to 48% of total length which has a hard finless tip.

The Round Sand Eel is a demersal species that is found within sandy substrate at depths up to 30 m (100 feet). They reach a maximum of 88 cm (2 feet 11 inches) in length. They feed on mobile invertebrates. The Round Sand Eel is an exceedingly rare species and is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, diet, growth, habitat, longevity, movement patterns, and reproduction.

The Round Sand Eel is a resident of Mexican waters of the Pacific but has a limited distribution being found only along the west coast of the mainland south of Manzanillo, Colima.

The Round Sand Eel is difficult to identify and is quite similar in appearance to the Panama Sand Eel, Bascanichthys panamensis (white head with brown mottling).

From a conservation perspective the Round Sand Eel is currently considered to be of Least Concern with stable, widely distributed populations They are exceedingly rare, seldom seen by humans, and of limited interest to most.