On the reproduction of two deep-sea Arctic holothurians, Elpidia heckeri and Kolga hyalina (Holothuroidea:Elpidiidae)

ABSTRACT Internal gonad morphology was examined in two species of elpidiid holothurians, Elpidia heckeri and Kolga hyalina, commonly occurring in the Central Arctic Ocean. The holothurians were sampled in August – September 2012 and in August 2018, at several locations in the Nansen and Amundsen Basins, in areas under the constant ice cover and in areas free of ice. Both species were observed at different reproductive stages and both are presumed to reproduce periodically. In 2012, spawning occurred at the beginning of September in Elpidia heckeri and from late August to early September in Kolga hyalina. There are reasons to believe that gametogenesis in K. hyalina depends on the availability of freshly deposited phytodetritus. The maximum oocyte size in Kolga hyalina (240 μm) was smaller than in Elpidia heckeri (390 μm).