Episode 490: Ipnops and Other Deep-Sea Fish

Further reading: Faceless Fish and the deep-sea voyages that found it Long-Lost &#8216;Faceless&#8217; Fish Shows Up Near Australia Ipnops: The faceless cusk [photo taken from the second article linked above]: A tripod fish: Show transcript: Welcome to Strange Animals Podcast. I’m your host, Kate Shaw. It’s a fish episode! These are also deep-sea fish, and you know how much I love deep-sea animals. Let’s talk first about some fish in the family Ipnopidae, including one deep-sea fish with the pleasing name of Ipnops. We know of three species of ipnops so far, but there may be more that scientists just haven’t found yet. Some scientists think there’s actually only one species, since all three species look almost identical but just live in different parts of the deep sea. Ipnops is sometimes called the grideye spiderfish. If you don’t know what it looks like, you may think the word spider in its name is the weird part. It’s not, and in fact I’m not sure where that comes from. It could be that the fish’s transparent fins look kind of like spiderwebs. Other fish in its family are called spiderfish too but are also sometimes called lizardfish. It feels like someone was in a goofy mood when naming these fish and just started saying random animal names. Ipnops only grows a little over 6 inches long at most, or 16 cm. It’s slender for its size, although its head is wider than its body. Its head is black but the color fades on the body until the tail is light gray. No, the weird thing about ipnops is its eyes. It doesn’t precisely have eyes, certainly not eyeballs. Instead it just has a thin layer of retinal cells spread across a divot in the top of its head, also called a photosensitive membrane or plate. These plates show up as yellow against the black head. Researchers think the fish can’t see the way we think of seeing, but it can probably sense bioluminescent light. Since it lives at the bottom of the deep sea where little to no light penetrates from the surface, it makes sense that ipnops doesn’t really need eyes. We still don’t know very much about ipnops or most of its relatives. It eats small crustaceans and all individuals produce both eggs and sperm. Ipnops eggs hatch into tiny larval fish that live near the surface of the ocean and have extremely large ordinary eyeballs. How these eyeballs transform into a retinal membrane is a mystery known only to ipnops. The family that ipnops belongs to, Ipnopidae, includes many species that are called tripod fish, and tripod fish are very weird too even though they have regular eyeballs, usually tiny ones. There are <span lang="en-