The species breeds in spring (Northumberland, England and Isle of Man). Fertilization is external. Females lay about 100 ova, each of which has a gelatinous coat, and all are embedded in a mucous mass secreted by a gland in the large urogenital papilla at the right rear of the mantle cavity. The mass, possibly adhesive as detritus coats some and about the size of the parent after the ova have absorbed water and expanded, is attached to algae or the underside of stones by anchoring protrusions of the mass moulded by the female’s foot. Frequently, several masses will be found together as the species tends to live gregariously. The trochophore and veliger stages are passed within the ova, and crawling, usually brown-shelled, young emerge to join the adults on rock or alga (photo J. Batten) flic.kr/p/67UC7w .

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