Fig. 1

Lineus viridis. Bouin fixation, paraffin section 5 μm thickness, Azan staining. Animals collected in the “Odde-Watt”, List/Sylt. a Infertile specimen, gonad located between two adjacent midgut diverticula (mgd), Mai 2005. b Gonad status in April 2005, reserve material is starting to be accumulated in a few eggs (asterisk). Animal were fixed 3 weeks after reproduction. c Gonad status end of July 2005. Eggs (asterisks) increased in size. It should be noted that the tissue closure between gonad and gonoduct (white arrow), gonopore is marked by a black arrow. d Gonad status in February 2006. More than ten large eggs are tightly packed inside the gonad. Due to the size, nuclei are not shown in this section. e Female fixed during mating envelope (me) production. Note spermatozoa inside the gonoduct (white arrow). f Mating cocoon consisting of the former mating envelope and an inner gelatinous layer (igl). bwm body wall muscles, ecm extracellular matrix, derm dermis, epi epidermis