The slender smooth-hound or gollumshark (Gollum attenuatus) is a species of ground shark in the family Pseudotriakidae. It is endemic to the waters around New Zealand, where it is usually found close to the bottom over the continental slope at depths of . An extremely slim, plain brownish shark reaching in length, the slender smooth-hound can be identified by its broad, flattened head with a long, distinctively bell-shaped snout. Its mouth is angular with short furrows at the corners, and contains a very high number of tooth rows in both jaws. Its two dorsal fins are roughly equal in size.
The diet of the slender smooth-hound is diverse, but dominated by small, benthic bony fishes and decapod crustaceans. It exhibits a specialized form of aplacental viviparity with oophagy: the females produce a single capsule in each uterus that contains 30–80 ova, of which one ovum develops into an embryo that consumes the rest of the ova and stores the yolk material in its external yolk sac. The growing embryo is mainly sustained by this yolk sac during gestation, though it may be additionally supplied with histotroph ("uterine milk") produced by the mother. The typical litter size is two pups, one per uterus. The International Union for Conservation of Nature (IUCN) has assessed the slender smooth-hound as Least Concern; it is taken as fishery bycatch but not in great numbers, and furthermore large portions of its range see minimal fishing activity.
Taxonomy and phylogeny
The first known specimen of the slender smooth-hound was a long adult male collected by the trawler Maimai in December 1953, at a depth of off Cape Palliser on New Zealand's North Island. It was preserved by the crew as a curiosity and given to ichthyologist Jack Garrick, who described it in a 1954 issue of the scientific journal Transactions of the Royal Society of New Zealand. Garrick named the species Triakis attenuata, in reference to its extremely slender ("attenuate") body.
In 1973, Leonard Compagno proposed a separate genus for the slender smooth-hound: Gollum, after the character in J. R. R. Tolkien's The Lord of the Rings, "to whom this shark bears some resemblance in form and habits." He placed Gollum with the finback catsharks (Proscylliidae), but also noted its many anatomical similarities to the false catshark (Pseudotriakis microdon). At the time, Compagno chose to maintain Pseudotriakis as the sole member of the family Pseudotriakidae because of its numerous unique traits. More recently, he and other taxonomists have increasingly tended to group Gollum and Pseudotriakis together in the family Pseudotriakidae. This arrangement was corroborated by a 2006 phylogenetic study by Juan Andrés López and colleagues, which found that the two genera have a high degree of genetic similarity across four protein-coding genes and form a natural clade apart from Proscyllium. An additional species of Gollum has now been described, and there is at least one additional species yet to be described.
Distribution and habitat
The range of the slender smooth-hound is restricted to the upper and middle continental slope around New Zealand, including submarine features to the north such as the Three Kings Ridge, the Challenger Plateau, and the Wanganella Bank. This uncommon species is mainly found between deep, but has been recorded from deep. It prefers a temperature of around and a salinity of approximately 34.8‰. Generally swimming near the sea floor, this shark inhabits both soft and rocky-bottomed habitats in terrain ranging from plateaus to steep slopes.
Description
The slender smooth-hound has a very thin body and a broad, highly flattened head. The snout is long, with a distinctive bell-shaped outline when viewed from above. The eyes have an elongate horizontal oval shape, and are equipped with rudimentary nictitating membranes (protective third eyelids). Beneath each eye is a prominent ridge, and behind is a much smaller spiracle. The nostrils are preceded by small, almost triangular flaps of skin. The line of the mouth forms an angle; there are very short furrows at the mouth corners. The upper and lower jaws contain 96–99 and 108–114 rows respectively of small, very closely spaced teeth; each tooth has a narrow upright central cusp flanked by smaller cusplets on both sides. The five pairs of gill slits are short.