The spiny dogfish and the spotted dogfish are egg-laying animals, releasing fertilized eggs with hard capsules. The egg capsule itself can look quite similar in these two species, but in the spotted dogfish the capsule is narrower and lighter in color. In addition, the egg capsule of the spiny dogfish has a thin material of protein on the outside to help it attach to things in its environment and to make it stiffer. Spiny dogfish often lay their eggs in kelp forests and on rocky bottoms. The small spotted dogfish has long threads in each corner that are attached to the stem of kelp. It takes about 4-5 months for the spurdog to emerge from the egg capsule. For the spotted dogfish, it takes about 5-11 months, usually 8-9 months, depending on the temperature. The shark is then 9-10 cm long.
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