Yolk formation in an annelid (Ophryotrocha puerilis, polychaeta)

The polychaete Ophryotrocha does not show a distinct breeding season. Egg masses are produced throughout the year (continuous breeder sensu Olive and Clark, 1978). A female specimen may contain up to three different generations of oocytes with oocyte growth and maturation in each batch being well synchronized. Oogenesis takes about 18 days from proliferation of the oogonia to mature eggs. In each segment pairs of sister cells interconnected by cytoplasmic bridges are located in outpocketings of the ventral mesentery which form the gonad wall. Presumptive oocytes and nurse cells are not easily distinguished at that time. Vitellogenesis is initiated while both oocytes and nurse cells are still in the ovary. Mitochondria, multivesicular bodies (transformed mitochondria ?), dense bodies, preformed yolk bodies of smaller size and lipid droplets are probably passed through the cytoplasmic bridge from the nurse cell to the oocyte. Yolk formation includes different mechanisms and materials of different origin. Autosynthetic yolk formation predominates during the first intraovarial growth phase. After detachment of oocyte-nurse cell-complexes from the gonad pinocytotic activity of nurse cells and particularly oocytes, increases considerably. The existence of coated vesicles suggests that external sources of yolk precursors contribute to yolk formation. Prior to oocyte maturation the remnants of the nurse cell are incorporated by oocytes.     

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.