Thanks to Lorenzo for this week's topic, carnivorous sponges! How can a sponge catch and eat animals? What is its connection to the mystery of the Eltanin Antenna? Let's find out!

Further reading/watching:

New carnivorous harp sponge discovered in deep sea (this has a great video attached)

How Nature's Deep Sea 'Antenna' Puzzled the World

Asbestopluma hypogea, beautiful but deadly if you're a tiny animal:

The lyre sponge, also beautiful but deadly if you're a tiny animal:

The ping-pong tree sponge, also beautiful but deadly if you're a tiny animal:

The so-called Eltanin antenna:

A better photo of Chondrocladia concrescens, looking less like an antenna and more like a grape stem:

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

This week we’re going to learn about carnivorous sponges, which is a suggestion from Lorenzo.

When I got Lorenzo’s email, I thought “oh, neat” and added carnivorous sponges to the giant, complicated list I keep of topic suggestions from listeners and my Aunt Janice, and also animals I want to learn more about. When I noticed carnivorous sponges on the list the other day, I thought, “Wait, sponges are filter feeders. Are there even any carnivorous ones?”

The answer is yes! Most sponges are filter feeders, sure, but there’s a family of sponges that are actually carnivorous. Caldorhizidae is the family, and it’s made up of deep-sea sponges that have only been discovered recently. We know there are lots more species out there because scientists have seen them during deep-sea rover expeditions without being able to study them closely.

We talked about sponges way back in episode 41, with some mentions of them in episodes 64 and 168 too, but only the filter feeder kind. Let’s first learn how a filter feeder sponge eats, specifically members of the class Demosponge, since that’s the class that the family Caldorhizidae belongs to.

Sponges have been around for more than half a billion years, since the Cambrian period and possibly before, and they’re still going strong. Early on, sponges evolved a simple but effective body plan and just stuck to it. Of course there are lots and lots and lots of different species with different shapes and sizes, but they almost all work the same way.

Most have a skeleton, but not the kind of skeleton that you think of as an actual skeleton. They don’t have bones. The skeleton is usually made of calcium carbonate and forms a sort of dense net that’s covered with soft body tissues. The tissues are often further strengthened with small pointy structures called spicules. If you’ve ever played a game called jacks, where you bounce a ball and pick up little metal pieces between each bounce, spicules sort of resemble jacks.

The sponge has lots of open pores in the outside of its body, which generally just resembles a sack or sometimes a tube. One end of the sack is attached to the bottom of the ocean, or a rock or something. The pores are lined with cells that each have a teensy structure called a flagellum, which is sort of like a tiny tail. The sponge pumps water through the pores by beating those flagella. Water flows into the sponge’s tissues, which are made up of lots of tiny connected chambers. Cells in the walls of these chambers filter out particles of food from the water, much of it microscopic, and release any waste material. The sponge doesn’t have a stomach or any kind of digestive tract, though. The cells process the food individually and pass on any extra nutrients to adjoining cells.

Obviously, this body plan is really effective for filter feeding, not so effective for chasing and killing small animals to eat. The sponge you may have in your kitchen is probably synthetic or manufactured from a sponge gourd, not an actual bath sponge animal, but it’s arranged the same way. Go look at that sponge, or just imagine it, and then compare it mentally to, say, a tiger.