Reproduction of the invasive fan worm <i>Branchiomma bairdi</i> (Polychaeta: Sabellidae)

<div><p></p><p>The fan worm <i>Branchiomma bairdi</i> 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 <i>B. bairdi</i> 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<sup>−2</sup>) and biomass (175 g m<sup>−2</sup>) occurred during August and September. Mature simultaneous hermaphrodite worms were found continuously throughout the annual cycle as well as asexual forms. In <i>B. bairdi</i> 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.</p> </div>