Lebenszyklus,Jugendentwicklung und Geschlechtsorgane von Rhabdomolgus ruber (Holothuroidea: Apoda)

Life-cycle, post-embryonic development, as well as organization and development of gonads, have been investigated in 1,970 specimens of Rhabdomolgus ruber Keferstein (1863), dredged near Helgoland from September 1968 to November 1969. The post-embryonic development is divided into 8 stages differing in number of tentacles. Five secondary tentacles are added, in regular sequence, to the 5 primary tentacles. There is only one reproductive period per year, which lasts from April to May. It is estimated that the life span of individuals ranges over 2 or 3 years. Cultivation experiments corroborate the values for duration of the 4 youngest stages calculated from the results of dredgings. Stage 1 (5 tentacles) lasts more than 44 days, stage 2 (5 to 6 tentacles) 11 days, stage 3 (5 to 7 tentacles) 12 days, and stage 4 (5 to 8 tentacles) 30 days. R. ruber hibernates at stage 5 (8 tentacles). The development of the gonad is analysed in detail from the first anlage in the pentactula to the condition in adult individuals. Eggs develop in the front part of the female gonad; yolk is produced in the inner epithelial layer of the middle part. The eggs migrate through the ovarial connective tissue to the tip of the ovary. R. ruber lives in the uppermost 2 cm of the sediment (“Amphioxus-sand”) near Helgoland (southern North Sea). Moving its tentacles over its mouth, the animal feeds from detritus. R. ruber is confined to the mesopsammal biotope. Adhesive capacity of glandular tentacles, resistance to mechanical damage, and direct ontogeny must be regarded as characteristic adaptations to mesopsammal life. The simple organisation of the gonads and the presumably free discharge of germ cells into the ambient sea water represent phylogenetically primitive properties of the species.