Abstract
The fan worm Branchiomma bairdi has been introduced to the Gulf of California from its original distribution in the Caribbean Sea, and is now a conspicuous component of most benthic communities. Study of reproductive features is essential to understand the dispersion capability of B. bairdi and its invasive potential. Sampling was carried out monthly in the port of Mazatlán during 2009 (23°12′13′′N, 106°24′31.4′′W). Abundance and biomass were measured. Sex and maturity were determined. Gametogenesis and observations on the spawning, fertilization, larval development and brooding are presented. The highest values of abundance (>2500 worms m−2) and biomass (175 g m−2) occurred during August and September. Mature simultaneous hermaphrodite worms were found continuously throughout the annual cycle as well as asexual forms. In B. bairdi gametogenesis is extra-ovarian. Three posterior thoracic segments and all abdominal segments are involved in the production of gametes. Sperm are ect-aquasperm type (free spawners with external fertilization). Spermatids are grouped in tetrads. Ovules are retained for intra-tubular fertilization. Larval development is lecithotrophic. Embryos are brooded on the collar and branchial crown.
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