It seems that every family hat its dwarf. The lantern sharks seems to contain the smallest shark species, and the finback catsharks include another very small shark species. But the family kitefin sharks (Dalatiidae) must like it small, considering the number of species with pygmy in its name. One of them is the spined pygmy shark.

Spined pygmy shark nmfs.jpg
Spined pygmy shark, image by SEFSC Pascagoula Laboratory; Collection of Brandi Noble, NOAA/NMFS/SEFSC –, Public Domain,

This little sharks mature at about 5.9 in -15 cm- (male) and 6.7 in -17 cm- (female) and reach only 8.7 in -22 cm- for males and 11 in -28 cm- for females. Its head looks like that of its relative, the cookiecutter shark, and the spined pygmy shark has got a cigar-shaped body and bioluminescent organs, too. It can be found all over the world at depths of 660–1,640 ft -200–500 m.

The spined pygmy shark and its sister, the smalleye pygmy shark, are the only sharks that have a spine on the first dorsal fin, but not the second. The spine is usually exposed in males and covered by skin in females.

Sources: here and here