1. What Kind of Shark Has a Cat's Name in Japan?
The Japanese bullhead shark (Heterodontus japonicus) lives on rocky bottoms and kelp beds in the northwestern Pacific, at depths of roughly 6 to 37 meters (20 to 121 feet). It grows to about 1.2 meters (4 feet) and has a short, wide head with a blunt, rounded, almost pig-like snout [1].
It belongs to the bullhead sharks, a family that Wikipedia describes as having ten living species. California's horn shark is another member. They are small, slow, and mostly active at night [2][3]. In Japan the name is neko-zame, which simply means "cat shark."
Be careful with that last word in English. Wikipedia lists "cat shark" among the alternative names for this species [1], but the standard English name is "Japanese bullhead shark." So the "cat" in the Japanese name does not appear in the usual English one.
2. Which Bumps Above the Eyes Look Like Ears or Horns?
Look at the face and you find the likely clue. Above each eye there is a shallow ridge of skin, and the space between the two ridges is slightly hollow [1]. Bullhead sharks in general have "pronounced ridges above their eyes" [2]. The horn shark's ridges are described as high, on a short, blunt head [3].
Two small lumps on top of a head, with a dip between them: that is the outline of a cat's ears, and also of a bull's horns. That fits what Japanese Wikipedia is reported to say: the cat in the Japanese name is the ridges seen as ears, and the English name is the same ridges seen as the horns of a bull [4]. I could not trace this to a record by whoever coined either name, so treat it as a reasonable reading rather than a proven origin.
The English side is similar. The Florida Museum lists "horn shark," "bullhead shark," "pig shark," and "horned shark" as English names for the California species [3]. Horns, bulls, and pigs: several English names for these sharks refer to familiar farm animals. Neither source explains who coined those names.
3. Do Japanese Dictionaries Agree on What the Cat Is?
They do not, according to the Japanese reference entries summarized for this site [4]. One encyclopedia says the cat refers to the face. Another says the head is large for the body and recalls a cat's head. A geology dictionary says the snout is shorter than in other sharks, giving a cat-like face. I only saw these through a secondary summary, and they are not mentioned in the English sources above.
So there are at least three candidate "cat" features: the whole face, the big head, or the ridges as ears. These could be one idea in different words, but the dictionaries do not say so. The best we can say is that the proposed explanations all point to the shark's head, and no record I found settles exactly where.
4. What Else Makes This Shark Unusual, Besides Its Names?
Names tell us how people saw the shark. The mouth tells us how the shark lives. The front teeth are small with a sharp central point, while the back teeth are broad and rounded [1]. In the horn shark, the side teeth are wide and molar-like, used for crushing [3]. The Japanese bullhead shark eats shelled animals and sea urchins, seizing them and grinding them up with its rear teeth [1].
The scientific name for the whole group, Heterodontus, is usually explained as Greek for "different teeth," which fits a mouth with two kinds of teeth. The sources I opened do not spell out that origin, so I am only passing it along as the common explanation.
The shark also "walks." It moves along the sea bottom with alternating motions of its paired fins [1]. And its eggs are strange: cases with thin flanges spiraling around the outside, like the thread of a screw [1]. For the horn shark, this shape lets the case be wedged into rocky crevices where predators cannot easily reach it [3].
5. So Why a Cat in Japan and a Bull in English?
One plausible answer, and it is my own inference from the descriptions, is that people in different places looked at the same lumpy head and saw whatever animal they knew best. The ridges above the eyes are a real feature that scientists mention in every description, so they are the best candidate. But "plausible" is as far as the sources let us go. Nobody I could find wrote down the moment of naming, and even the Japanese dictionaries disagree.
That is a useful lesson about animal names. A name can be a clue about how people once saw something, and it can still be a guess. When you find a neat origin story, it is worth asking: who said this, and how did they know?
If you want to look for yourself: at an aquarium with bullhead or horn sharks, find the ridges above the eyes and decide whether you see ears, horns, or something else. Watch from outside the glass. Bullhead sharks have sharp spines on their dorsal fins, and the Florida Museum notes that horn sharks may bite when harassed, so never reach into a tank or try to touch one.