Gonadogenesis, embryogenesis, and unusual oocyte origin in Notogaeanemertes folzae Riser, 1988 (Nemertea, Hoplonemertea)

Abstract

Notogaeanemertes folzae Riser, 1988, is asupralittoral hoplonemertean from New Zealand alliedto the ’group 1‘ terrestrial and semiterrestrialgenera. The original description noted that it, likea few other ‘group 1’ forms, is hermaphroditic andthat it is viviparous. The present study found that,in addition to testes and ovaries, mature individualscontain mixed gonads, most with testis tissuepredominating and some oocytes in various stages ofdevelopment, but also some of primarily ovariancharacter with spermatogenic nodules. Oogenesis inthis species appears to be unique among nemerteans. Small immature oocytes are found embedded among theganglionic cells of the lateral nerve cords, fromwhich they appear to erupt and migrate into theparenchyma where differentiation takes place alongdivergent pathways leading to functional ovaries ortestes. No anlagen for gonads, other than theerupting oocytes, have been found. Embryonicdevelopment is described and is generally similar toother viviparous nemerteans, except that developinggonads can be found in large embryos. In one case aportion of the sac containing the embryo is comprisedof testis tissue. New morphological observations onother organs and tissues of this species are alsopresented.