A giant transparent orb discovered by a team of deep-sea divers off the coast of Norway was home to hundreds of thousands of soon-to-be squid hatchlings.

A video captured by researcher Ronald Raasch shows the “once-in-a-lifetime encounter” as one of his team’s divers slowly swims alongside the floating mass, shining a flashlight through its translucent walls. The team was swimming back toward the research vessel REV Ocean in the cold waters outside of Ørsta, Norway after diving at a WWII shipwreck 200 meters (656 feet) from the coast, according to a description accompanying the video.

Described as “blekksprutgeleball” – or “cephalopod jelly ball” in Norwegian – the orb-like ball is the egg sac belonging to Illex coindetii, or the southern shortfin squid. It was floating in the middle of the water column, about 17 meters (55 feet) below the surface and 15 meters (49 feet) above the ocean floor. I. coindetii is a member of the Ommastrephidae family and its egg sacs have been found on both sides of the Atlantic Ocean, from as far north as Norway southward to the Mediterranean Sea. The species was first reported by the French researcher Jean-Baptiste Verany in 1837 and remains an important source of food for humans today.

Spheres average about 1 meter in diameter (3 feet) with more than half of them being identified as having a dark streak through their center as they float freely through the water column. Females can hold as many as 50,000 to 200,000 mature eggs in the ovary and oviduct. Spawning occurs all year long but varies depending on the season, lasting from just a few days to a few weeks, according to Sealife Base. Embryonic development of the eggs typically takes between 10 and 14 days at temperatures of 15°C (59°F). When hatched, the squid juveniles are active swimmers and make their way through the water column via jet propulsion.

Raasch and his team have reported on the egg sacs in the past as part of a volunteer effort.

“For two years (2017-2019) we have gathered around 80 observations of large gelatinous spheres. The oldest [is] about 30 years old, and the youngest a few weeks,” wrote members of the Gelatinous Sphere Project in a statement.

A study published last year by the same team reported 27 “large, gelatinous spherical masses” that were similarly observed in European waters across the continent, from Norway and Sweden to Croatia and Italy between 2001 and 2017.

“Individual spheres measured 0.3–2 m in diameter, averaging one meter, with all but four sighted in suspension in the water column between 0.5 and 52 m depth, in water temperatures ranging between 10–21 degrees Celsius,” reported the authors in Marine Biology Research.

The scientists say they will publish their current observation at a later date.