Reproductive biology of several species of recently collected pelagic nemerteans

The reproductive biology and morphology of six polystiliferous and one monostiliferous species of pelagic nemerteans was studied in specimens recently collected off California. Depth distributions for these specimens ranged from 250 m to 3250 m, with most specimens obtained between 700 m and 1750 m. Length of sexually mature individuals ranged from 2 mm for the monostiliferan to 61 mm for a male Phallonemertes cf. murrayi. Among P. cf. murrayi and Nectonemertes cf. mirabilis, which yielded the largest specimens studied, mature males were larger than mature females and mature animals were larger than those in which gonads were not apparent. Females typically outnumbered males, although N. cf. mirabilis approached a 1:1 sex ratio. In the polystiliferans studied by light microscopy, accessory ovarian cells appeared to translocate yolk or yolk precursors to oocytes via cytoplasmic bridges, a mechanism typically associated with nurse cells and not previously reported from nemerteans. Mature oocytes 0.5-1 mm in diameter were common, making them very large compared to those of benthic nemerteans. Sperm possessed elongated heads and nuclei. In general, the pelagic nemerteans studied appeared: a) to produce relatively few mature gametes at a time, b) spawn in close proximity to each other, c) undergo iteroparous reproduction, and d) display moderately long-lived life cycles. In addition, data for P. cf murrayi and possibly N. cf. mirabilis demonstrates potential seasonal peaks in reproductive activity.