largetooth cookiecutter shark

Taxonomy:

Phylum– Chordata

Class– Chondrichthyles

Subclass– Elasmobranchii

Order– Squaliformes

Common Name– Dogfish Sharks

Family– Dalatiidae

Common Name– Kitefin Sharks

Genus– Isistius

Species– plutodus

Status: IUCN Red List LEAST CONCERN

Average Size and Length: The Largetooth Cookiecutter shark reaches a maximum known length of 16.5 inches.

Teeth and Jaw: The mouth of the Largetooth Cookiecutter shark is transverse, with a deep fold enclosing its corners and fleshy suctorial lips. The jaws are larger and more powerful than those of the Cookiecutter shark, and contain fewer tooth rows, numbering around 29 in the upper jaw and 17-19 in the lower jaw. The upper teeth are small, narrow, and smooth-edged, upright at the center of the jaw and becoming more angled towards the corners. The lower teeth are enormous; the largest teeth relative to body size of any living shark. They are much bigger than the lower teeth of the Cookiecutter shark. They are triangular in shape, with minutely serrated edges and interlocking rectangular bases.

Head: The Largetooth Cookiecutter shark has an extremely short, blunt head and snout. The large, oval eyes are positioned forward, to allow binocular vision, and are followed by wide, angled spiracles. The nostrils are small, each with a low, pointed skin lobe in front.

Tail: The caudal fin is very short and asymmetric, with the upper lobe twice as long as the lower and bearing a prominent ventral notch near the tip.

Demographic, Distribution, Habitat, Environment and Range: Only ten specimens of Largetooth Cookiecutter shark are known, caught from a handful of widely scattered localities: off Alabama in the United States, Bahia in Brazil, the Azores, and Western Sahara in the Atlantic Ocean, and off Okinawa and New South Wales in the Pacific. Those captures were made in the epipelagic zone 200–660 feet down, close to land over continental shelves, continental slopes, or oceanic trenches that may descend as far as 4 miles down. Possibly bathypelagic.

Diet: The Largetooth Cookiecutter shark feeds by gouging out chunks of flesh from larger animals, including bony fishes, sharks, and marine mammals, and is able to take larger bites than the Cookiecutter shark.

One study has found that the Largetooth Cookiecutter shark is responsible for 80% of the Cookiecutter wounds found on cetaceans off Bahia, Brazil. The flank was the most often-attacked area, followed by the head and abdomen. In at least three cases, bites to dolphins appeared to have resulted in their subsequent deaths by abandoning.

Ram-Suction Index: Both. The Largetooth Cookiecutter shark is a facultative ectoparasite that feeds by excising plugs of flesh from larger animals. While the Cookiecutter shark is conceived to latch onto the surface of its prey and bite with a twisting motion, producing a circular wound containing spiral grooves inside from its lower teeth, the Largetooth Cookiecutter shark seems to engage in a “sweeping” bite that produces a larger, more elongate (twice as long as the width of the mouth), oval wound containing parallel tooth grooves.

Aesthetic Identification: The Largetooth Cookiecutter shark has a long, cigar-shaped body. They are plain dark brown, with translucent margins on the fins and sparsely scattered bioluminescent, light-emitting photophores on the belly that are most likely used in counter illumination. Most specimens have lacked the dark “collar” found on the throat of the Cookiecutter shark. However, a specimen caught in 2004 off the Azores did possess the collar. They have 5 pairs of small gill slits. The small dorsal fins have rounded tops and are placed far back, on the last third of the body. The first dorsal fin originates slightly ahead of the pelvic fins, while the second dorsal originates closely behind and measures almost a third again the height of the first. The pectoral fins are small and rounded and positioned relatively high on the body behind the fifth gill slit. The pelvic fins are tiny, and there is no anal fin.

Biology and Reproduction: The Largetooth Cookiecutter shark is thought to be ovoviviparous.

Behavioral Traits, Sensing and Intelligence: Based on its smaller dorsal and caudal fins, the Largetooth Cookiecutter shark is believed to be less active than the Cookiecutter shark, which is already a poorly active and swimming shark. Much of the Largetooth Cookiecutter sharks body cavity is occupied by an enormous oil-filled liver, which allows it to maintain neutral buoyancy in the water column with little effort.

Unlike the Cookiecutter shark, the Largetooth Cookiecutter shark has binocular vision. The Cookiecutter shark has retinal ganglion cells concentrated in a concentric area rather than in a horizontal streak across the visual field.

The Largetooth Cookiecutter shark is a facultative ectoparasite.

Speed: It is an even weaker swimmer than the already weak-swimming Cookiecutter shark.

Largetooth Cookiecutter Shark Future and Conservation: Other than possibly damaging billfishes or other valued species, the Largetooth Cookiecutter shark is of no importance to commercial fisheries. All but one of the known specimens have been caught as bycatch in commercial trawls or longlines.

Largetooth Cookiecutter Shark Recorded Attacks on Humans: Potentially dangerous to humans given its behavior, but not considered a threat.