Did you know that pectoral fins can serve many different purposes? Flying fish use them for gliding, anglerfish or epaulette shark for walking, the helmet gurnard to scare away predators and the sea robin for chemo-reception and courtship. Most fish swim by generating undulatory waves through the caudal fin, but there are many fish using their pectoral fins for propulsion, too -the most impressive are manta rays. Sharks normally use them only to stay afloat (like airplane wings by dynamic lifting). But a little (approx. up to 20 in -50 cm- long) shark called taillight shark (Euprotomicroides zantedeschia) uses its pectoral fins, which are muscular and enlarged into rounded paddles, for propulsion, too.

image source: Second ever pocket shark discovered

Like its much cuter cousin, the pocket shark, the taillight shark has got a pouch on its belly, but this one is known to emit clouds of luminescent blue fluid.

image source: Second ever pocket shark discovered

This is most likely the reason for the name “taillight” – since the tail itself, like the rest of the body, has got only a few small, light-emitting photophores and no other “light” source. It could be a clever way to attract prey for the little deep sea predator with its large mouth and small and needle-like upper teeth and large and triangular lower teeth. Their bases are interlocking to form a continuous cutting surface, like in the case of its other cousin, the cookiecutter shark, but unlike it, the lips of the taillight shark are not modified to be suctorial.

Sources: herehere, here and here