Even after fully absorbing the yolk sac, the pups may live in the uterus for a period of time afterwards during the gestation period. Both sexes are greyish brown in color and are countershaded. Males are identified by a pair of pelvic fins modified as sperm-transfer organs, or "claspers". The male inserts one clasper into the female cloaca during copulation. In females the size of ova and the state of uteri determines whether sexual maturity has been reached, while in males, clasper length and calcification is the determination factor. Many of the growth patterns show a isometric growth pattern, as the pups have very similar features to the adults. Sexual maturity does not match body size development, they mature quite earlier than one would expect. Most males reach sexual maturity at an earlier ages of around 10 years, growing to be about 60–65 cm in length. Females take a longer period of time, around 16 years, to reach sexual maturity, and can grow to about at that time. Some dogfish have been seen to live nearly 70 years, but the average lifespan is around 30–40 years. Male Spiny dogfish use their claspers to impregnate females, which take time to develop properly, and before reaching sexual maturity, tend to be longer than their pelvic fins. During this time, the testes develop, but no sperm will exist inside until later stages are reached, and genital ducts are deformed compared to adult ducts. Once the adult stage is reached, claspers have elongated, and are now hardened with calcium and are still slightly longer than their pelvic fin. At this point testes are fully developed, and sperm exist within the seminal vesicles, and genital ducts conform to a twisted shape we commonly see in adults. Spiny dogfish are bottom-dwellers. They are commonly found at depths of around , but have been found deeper than . Life span estimates based on analysis of vertebral centra and annuli in the dorsal spines range from 35 to 54 years. Commercial use Spiny dogfish are sold as food in Europe, the United States, Canada, New Zealand, Venezuela and Chile. The meat is primarily eaten in England, France, Italy, the Benelux countries, Germany, and as an unwitting houndshark in Greece. The fins and tails are processed into fin needles for cheaper versions of shark fin soup in Chinese cuisine. In England, dogfish are bought in fish and chip shops