Reproductive biology of several species of recently collected pelagic nemerteans

The reproductive biology and morphology of six polystiliferous and onemonostiliferous species of pelagic nemerteans was studied in specimensrecently collected off California. Depth distributions for these specimensranged from 250 m to 3250 m, with most specimens obtained between 700 m and1750 m. Length of sexually mature individuals ranged from 2 mm for themonostiliferan to 61 mm for a male Phallonemertes cf. murrayi. Among P. cf.murrayi and Nectonemertes cf. mirabilis, which yielded the largest specimensstudied, mature males were larger than mature females and mature animalswere larger than those in which gonads were not apparent. Females typicallyoutnumbered males, although N. cf. mirabilis approached a 1:1 sex ratio. Inthe polystiliferans studied by light microscopy, accessory ovarian cellsappeared to translocate yolk or yolk precursors to oocytes via cytoplasmicbridges, a mechanism typically associated with nurse cells and notpreviously reported from nemerteans. Mature oocytes 0.5–1 mm indiameter were common, making them very large compared to those of benthicnemerteans. Sperm possessed elongated heads and nuclei. In general, thepelagic nemerteans studied appeared: a) to produce relatively few maturegametes at a time, b) spawn in close proximity to each other, c) undergoiteroparous reproduction, and d) display moderately long-lived life cycles.In addition, data for P. cf. murrayi and possibly N. cf. mirabilisdemonstrates potential seasonal peaks in reproductive activity.