You can distinguish the smooth hounds from all other British sharks by their teeth. Most sharks (almost by definition) have large, sharp, usually triangular teeth with serrated cutting edges, or else long thin stabbing teeth – but the smooth hounds have flattened blunt teeth in both top and bottom jaws. They are sometimes referred to as ‘ray-toothed’ sharks – and their jaws do indeed look like the flattened ‘pavement’ of teeth seen in rays.
Apart from their teeth, the smooth hound and the starry smooth hound have all the characteristic features of sharks: a long slender body, a notched, asymmetrical tail, two large dorsal fins, one anal fin and broad
Both the smooth hound and the starry smooth hound are greyish on the back and upper sides and creamy on the belly. The starry smooth hound, however, is covered with small white spots, each smaller than the pupil of the eye. These spots resemble the stars that give it its name. The smooth hound does not have white spots.
Vive la difference
It is quite extraordinary that, while the differences in appearance between the two sharks are so subtle that they are difficult to identify, their breeding biology is fundamentally different. Both bear their young live, but the way the pups develop as embryos in the two species is poles apart. The starry smooth hound is ovo-viviparous – the young develop within the mother and are nourished only by the yolk in the egg. Up to 28 pups are produced at a time, each about 30cm (12in) long. The smooth hound, on the other hand, is viviparous – the young develop inside the mother but, late in development, derive their nourishment directly from her. The yolk sacs establish contact with the mother’s uterine wall to form a false placenta. This is very rare in fish. The smooth hound gives birth to litters of up to 15 pups, each about 30cm (12in) long.
The young of both species are born in the summer, after a gestation period lasting about 12 months.
Crunch, crunch, crunch
Both smooth hounds feed almost entirely on crustaceans. Their flattened teeth are designed to cope with a diet of hard-shelled animals. Large smooth hounds tackle hermit crabs in great numbers, not troubling to pick them out of their protective whelk shell but scrunching them up, shell and all. Both species of shark are thought to feed mainly at night.