Occasional sexual reproduction significantly affects the population structure of the widespread, predominantly asexually reproducing marine worm Lineus sanguineus (Nemertea: Pilidiophora)

Abstract Asexual reproduction by fissiparity has only been described from very few of the approximately 1300 nemertean species that otherwise mainly reproduce sexually. The best studied fissiparous species, Lineus sanguineus (Rathke 1799), is a cosmopolitan heteronemertean inhabiting intertidal habitats temperate coasts. Although sexual never described, molecular data suggest substantially shapes genetic structure investigated populations. In an attempt to clarify extent reproduction, three gene fragments (COI, 16S, ITS) were sequenced for 108 specimens sampled in 8 European localities. results phylogenetic analysis and haplotype network showed no clear distinction between different populations, thus indicating presence reproduction. Furthermore, we provide circumstantial evidence comparably long-lived planktonic larval stage as present closest relatives L. . To further understand impact abiotic factors on fissiparity, effect temperature illumination regimes reproductive behavior fragmentation was population Bergen, Norway share same haplotype. Experimental setups represented summer (long light period elevated temperature) winter (short decreased conditions. Under conditions, higher number animals remained sexually mature at least one specimen shed eggs occasion. Thus, although short and/or low temperatures are most likely influential maturity, influence less clear. this study solidify status structuring species. addition, provides first dynamics asexual modes which future investigations will have expand, especially regarding physiological aspects.