Reproduction and Larval Development of Spio Setosa (Spionidae; Polychaeta)
Abstract:The reproductive system of Spio setosa is limited to the central epitokal region of the body. Externally, sexes may be distinguished by the color of genital products visible through the body wall: white in males; yellow to pink in females. The sex ratio is 1 : 1. Males possess one pair of testes attached to the walls of the nephridial canals in each epitokal segment, and spermatogenesis occurs free in the coelom. Mature sperm are of the elongated “aberrant” type with a unique spiral of chromatin in the head. Females possess one pair of ovaries and a pair of intra-epidermal seminal receptacles in each epitokal segment. The atokal nephridia of both sexes become modified at maturity and serve as genital ducts.
Spawning occurs in the spring (March) and fall (October). Eggs are laid in a mucous egg mass within the tube of the female. One fourth of the spawned eggs are fertilized, the remainder serving as food for developing larvae.
Development following the spring spawning occurs entirely within the parent tube and is described in detail. Adelphophagia begins in the late metatrochophore and continues to the 7-segment stage, when the adult mode of feeding begins. Larvae metamorphose at the 15-17 segment stage, leaving the parent tube and burrowing into the surrounding substratum. After metamorphosis, nephridia appear.
Following the fall spawning, a pelagic larvae, as yet unrecognized, is probably formed.
Document Type: Research Article
Publication date: 1967-06-01
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