Invertebrates with bones?

Are there any? I could not think of any.

Um, doesn’t that kind of contradict the meaning of the word? How can you have bones without having a skeleton?

Some arthropods have internal supporting skeletal structures - that is to say, it’s not just an exoskeleton they have.

Invertebrate means it is without a spine, not an entire skeleton.

Well, invertebrates (every animal species not Chordata) by definition have no spinal column, which wouldn’t necessarily preclude them from having other bones . . . but in practical terms, you’re spot-on.

AFAIK, the only other phylum that comes close is Echinoderma–sea stars, cukes, and urchins. Their plates and spines are ossified, and probably as close to proper bone as an invertebrate will get.

Wellnow, do you want to know about bones or skeletons? There are plenty of critters with exoskeletons, of course, some with hydroskeletons, and some running the Hybrid Synergy Skeleton (cuttlefish come to mind).

The Giant Pacific Gumboot Chiton has eight butterfly shaped skeletal plates, which are kind of like bones.

Cuttlefish (a relative of the squid) have cuttlebone. wiki: Cuttlefish possess an internal structure called the cuttlebone, which is composed of calcium carbonate and is porous, to provide the cuttlefish with buoyancy. Buoyancy can be regulated by changing the gas-to-liquid ratio in the chambered cuttlebone. Each species has a distinct shape, size, and pattern of ridges or texture on the “bone”. Cuttlebones are traditionally used by jewelers and silversmiths as moulds for casting small objects. They are probably better known today as the tough material given to parakeets and other cage birds as a source of dietary calcium. The cuttlebone is unique to cuttlefish, one of the features contrasting them with their squid relatives.

“Bone” is defined to be what vertebrates have, but if you mean bone-like structure, then I think the question has been answered. For it to be a “bone”, though, it has to be in a vertebrate.

FWIW, in re the cuttlefish, I seem to recall that their “bone” derived from an absorbed exoskeleton.

Right. “Bone” refers to a specific kind of tissue, which only vertebrates have. The main mineral in bone is calcium phosphate. Vertebrates are nearly unique among animals in having a skeleton made of calcium phosphate.

The hard shells of mollusks are made up of calcium carbonate, in the form of calcite or aragonite. This includes the so-called cuttlebone of cuttlefish, which is really just an internal shell.

The hard parts of insects are made up of chitin. The exoskeleton of crustaceans is made up of chitin, often reinforced with calcium carbonate.

Actually, invertebrates are animals not in the subphylum Vertebrata. The phylum Chordata, which subsumes Vertebrata, consists of all animals which develop a notochord. In vertebrates, this notochord develops into a bony vertebral column. (There are other subphyla of Chordata whose members develop neither vertebrae nor any other bones.)

As it happens, there is one branch of chordates which develop bones but no vertebrae: the hagfish. They have bony skulls, but their notochord is never replaced with a vertebral column, making them literal invertebrates.

The actual taxonomy of hagfishes is uncertain. Most biologists consider them to be degenerate vertebrates and place them in Vertebrata even though they have no vertebrae.

Not really an exoskeleton, just a shell as in the nautilus.