Espen Bergersen / Close-up of a spyhopping Humpback whale (Megaptera novaeangliae) showing the knobs (tubercles) which are enlarged hair follicles possibly used for sensory purposes. Kvaloya, Troms, Northern Norway. No...

Espen Bergersen / Close-up of a spyhopping Humpback whale (Megaptera novaeangliae) showing the knobs (tubercles) which are enlarged hair follicles possibly used for sensory purposes. Kvaloya, Troms, Northern Norway. No...

Chris Mattison / Australian barking gecko (Underwoodisaurus milii) scales from shed skin, showing granular scales with scattered tubercles.

Mark Carwardine / Humpback whale (Megaptera novaeangliae) surfacing, showing bloodied tubercles from fighting, Sea of Cortez, Baja California, Mexico

Mark Carwardine / Humpback whale (Megaptera novaeangliae) at surface showing bloodied tubercles on head during courtship battle, Sea of Cortez, Baja California, Mexico

Steven David Miller / Humpback Whale (Megaptera novaeangliae) spyhopping near boat, Hervey Bay, Queensland, Australia

Chien Lee / Curved Spiny Spider (Gasteracantha arcuata) showing unusual tubercles with unknown function, Lambir Hills National Park, Borneo, Malaysia

Chien Lee / Curved Spiny Spider (Gasteracantha arcuata) with unusual tubercles with unknown function, Lambir Hills National Park, Borneo, Malaysia

Flip Nicklin / Humpback Whale (Megaptera novaeangliae) spyhopping showing bumps called tubercles, vulnerable, southeast Alaska

Flip Nicklin / Humpback Whale (Megaptera novaeangliae) spyhopping showing bumps called tubercles, vulnerable, southeast Alaska

Joel Sartore / Photo Ark / Tricolor shiner (Cyprinella trichroistia) male with nuptial tubercles, Goodwater, Alabama. Captive.

Brian Bevan / Minnow (Phoxinus phoxinus) group of breeding males showing tubercles, Bedfordshire, UK, May.