Finback Catsharks — 5 species &
False Catsharks — 4 species
Closely related to the scyliorhinids are the finback catsharks (Proscylliidae), which includes the smallest carcharhinoid: the Pygmy Ribbontail Catshark (Eridacnis radcliffei); this species matures at about 6 to 7.5 inches (15 to 19 centimetres), rivaling the smallest squaloids in size. In addition to its small size at maturity, this species is remarkable for the large size of its pups compare to with their mother: a 7-inch (18-centimetre) female might give birth to one or even two 4.3-inch (11-centimetre) pups. It is possible that female Pygmy Ribbontails grow considerable when pregnant as only the larger females contain near- or full-tem fetuses, while small females contain only embryos.
The False Catshark (Pseudotriakis microdon) is a rare, deep-sea species, generally inhabiting abyssal slopes at depths between 660 and 4,900 feet (200 and 1,500 metres). Growing to a length of about 10 feet (3 metres), this little-known shark is among the largest of carcharhinoids.. The False Catshark is rather slender in overall body form, characterized by a long, low first dorsal fin, long narrow eyes (seemingly frozen in a permanant 'squint'), and long, teardrop-shaped spiracles. The huge, oily liver, mush musculature, soft fins and skin of the False Catshark suggest that it is relatively inactive and sluggish. Due to its many odd features, this species was long considered to be the sole member of the family Pseudotriakidae, but new evidence suggests that it is closely related to the Slender Smoothhound (Gollum attenuatus — the only shark named after a character in Tolkein's Lord of the Rings trilogy), which is therefore also placed in that family. Recent work by ichthyologist Kazunari Yano off Okinawa, Japan, and Three Kings Ridge off New Zealand, has revealed a few secrets about this animal's reproductive biology. Males of this species mature at a length of about 8 feet (2.4 metres), while females mature at a length of about 9 feet (2.8 metres). Gestation period in the False Catshark remains unknown, but two pups are typically born per litter, each about 2.5 feet (75 centimetres) long. For decades it had been known that adult female False Catsharks produce an astonishing number of eggs — some 20,000 in one ovary of a 9-foot specimen from the western Indian Ocean. Thanks to Yano's work, we now know that these eggs are used as an accessory food source for False Catshark pups to fuel late stages of their development. Although intrauterine oophagy (egg-eating) occurs in most — possibly all — mackerel sharks (order Lamniformes), the False Catshark provides one of only two known cases of this form of fetal nutrition in a non-lamnoid shark (the other case is the Tawny Nurse Shark [Nebrius ferrugineus], an orectoloboid).