The pygmy shark has a large head and underslung jaw, strangely shaped caudal fin, and a very small first dorsal fin set far back on the body. They have no spines in front of the dorsal fins. The colour is black with a slightly paler belly and white borders to the fins. The lower body is luminescent, which is thought to help in disguising the fish's dark silhouette from upward-looking predators below.
Pygmy sharks undertake vertical migrations from the lower levels of their depth range to the surface each night. They are following the deep-water crustaceans, squids, and bony fish, which also rise at the same time to feed on surface plankton in comparative safety.
Reproduction is ovoviviparous, meaning that they produce eggs that develop inside the mother's body and hatch immediately after their release from the parent. A female pygmy shark produces about 8 young in a litter.
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