Did you know that there is a little shark who lays eggs shaped like a screw? That is the horn shark.

As all species of the family bullhead, horn sharks have got a pig-like snout, a small puckered mouth, ridges over the eyes, a chubby little body and fin spines. They live in kelp forests on the bottom and swim wriggly and slow or clamber on their pectoral fins. They are between 15 cm (6 in) – after hatching – and 1.2 m (4 ft) long. Juvenile horn sharks feed on worms and tentacles of anemones. As adults, horn sharks use suction to capture prey like sea urchins and crustaceans, which is grasped by the anterior conical teeth and then crushed by the posterior molar-like teeth. After swallowing it all, they regurgitate the hard parts later. To dislodge firmly attached prey the adult horn shark is known to use its protrudable upper jaw as chisel or its entire body as lever.

Female horn sharks lay up to 24 eggs over a period of four month. Due to their awkward shape, each horn shark egg case requires several hours to rotate out of the mother shark’s cloaca. After that, the mother takes the egg in her mouth and wedges it into a crevice. Once it hardens, the egg case turns from light to chocolate brown and is difficult for most predators to remove without benefit of opposable thumbs. But large predatory snails are able to break into the egg cases, and seals are known to eat horn shark eggs, too.

The characteristic fin spines are an effective anti-predator device, discouraging larger fishes from eating horn sharks, especially juvenile ones. On several occasions, pacific angel sharks off California have been filmed swallowing juvenile horn sharks, even newborns, only to disgorge them with much haste and apparent disgust. After that, the horn shark swam away as though nothing had happened.

Sources: here and here.

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