Three new species of Fritillaria are described from specimens collected by a remotely operated vehicle (ROV) between 180 and 735 m depth in Monterey Bay, California. Fritillaria rex becomes the largest species now described for this genus (trunk length up to 10 mm, tail length up to 18 mm). This species is characterized by five or six narrow muscle bundles on each side of the tail, slit-shaped spiracles, a spherical ovary and a cylindrical testis. Fritillaria amphigonadis (trunk length up to 5.2 mm, tail length up to 7.5 mm) is characterized by two narrow muscle bundles on each side of the tail, slit-shaped spiracles, paired spherical ovaries, and a unique pi-shaped testis. Fritillaria lucifer (trunk length up to 4.1 mm, tail length up to 7.0 mm) has 12 extremely thin muscle bundles distributed broadly across the tail, rounded spiracles, a spherical ovary and a U-shaped testis. An additional mesopelagic Fritillaria appears to be consistent with the description of the Mediterranean F. fage, but specific differences in pharyngeal cells, cellular patterns on the tail, and gonadal morphology suggest that the specimens from Monterey Bay are a new variety, F. fagei mbarii. Based on the relatively limited number of collections (i.e. only 20 specimens yielding four unique taxa), it would appear that the possible diversity of larvaceans that live below the surface mixed layer is significantly underestimated.
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