"Urticating spines beneath their exuberant hair"

Something is not quite clear to me about these caterpillars Franz is interested in.

"Urticating spines"--ok, that makes sense--spines which cause itching.

"beneath their exuberant hair"--wait a minute. Hair is a quintessentially mammalian trait, along with the modified sweat glands which are nipples. These beasties are invertebrates. How can you have hair--an epidermal projection (as I learned in comp anatomy), or a Skin appendage, which is-a Subdivision of epidermis (as defined in the Foundational Model of Anatomy [FMA])--when you don't even have an epidermis?

Yet it certainly does look like hair in the first photo, doesn't it? This is interesting enough to check out. I will put it on the list, right after beaver cloacae and "persistent male uteri", to investigate.

My guess is that it is homoplastic and analogous, but not homologous. More on those concepts and the exuberant locks of itchy-making poisonous caterpillars later.