Life-history biology of Peniagone azorica and P. diaphana (Echinodermata: Holothurioidea) from the north-east Atlantic Ocean

Aspects of the reproduction and population biology of two elasipodid holothurians collected during the period 1973–1984 from the north-east Atlantic Ocean were examined. The reproductive biology of both the benthic species Peniagone azorica and the benthopelagic P. diaphana are similar. A primary oocyte forms from an oogonium and grows to about 100m diameter, whereupon it undergoes vitellogenesis and increases to 300m before being spawned. A high proportion of primary oocytes are not spawned and undergo a complicated breakdown process resulting in the formation of an amorphous sac in the ovary wall. It is possible that when an ovarian tubule is full of these sacs it atrophies and drops off, allowing other tubules to develop. The maximum egg size for both species suggests abbreviated larval development. In P. azorica, juveniles reach sexual maturity for the first time at about 30 mm length. The population structure suggests that the adults grow slowly, although it is possible that the observed unimodal distribution in size-frequencies results from one or several recruitments. Recruitment to the population is probably infrequent and may occur irregularly. Comparison of the population structure of closely spaced samples suggests a patchy distribution on the bottom. The benthopelagic lifestyle of adult P. diaphana suggests that the larvais also planktonic.