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Bau und Lebensgeschichte des Polypen vonTripedalia cystophora (Cubozoa, class. nov., Carybdeidae) und seine Bedeutung für die Evolution der Cnidaria

1975; Springer Nature; Volume: 27; Issue: 4 Linguagem: Inglês

10.1007/bf01611150

0017-9957

B. Werner,

Aquatic Ecosystems and Phytoplankton Dynamics

FollowingHaeckel (1880), most zoologists have grouped the Cubomedusae with the class Scyphozoa. However, the actual systematic position and evolution of the Cubomedusae remained unclear because essential phenomena of the life cycle, i. e. life history and structure of the polyp generation and the process of medusa formation were unknown. Successful cultivation of the Carribean larviparousTripedalia cystophora Conant, 1898 elucidated for the first time the complete life cycle of a cubomedusa. Primary polyps could be raised from planulae which were transferred by air mail from La Parguera, Puerto Rico. The sessile polyp is solitary. Its morphology, anatomy, and behaviour are described. The body (length 0.6–1.0 mm) is radially constructed without any trace of tetramerous structures. 6 to 11 solid capitate tentacles insert in one circle, above which the body ends in a long contractile snout-like mouth cone (proboscis). The body is sac-like without gastric septa or gastric pockets; its base is enveloped by a small cup of thin, structureless periderm. Asexual reproduction by which the stock is enlarged quickly envolves lateral budding of small secondary polyps. After detachment these small polyps go through a creeping phase. The fully grown polyp shows a remarkable behavioural plasticity as it can migrate and change into an inactive encysted stage. The whole polyp metamorphoses into a single medusa. All externally visible metamorphosis phases are described. First, the polyp's body becomes tetramerous due to 4 longitudinal folds. The tentacles congregate into 4 groups, each in one quadrant. While the distal parts of the tentacles are resorbed, their bases develop into 4 perradial sensory organs (rhopalia). Interradially, 4 new tentacles are formed and become the primary tentacles of the medusa. Simultaneously, the complete body of the polyp transforms into the bell of the medusa. At the end of the metamorphosis which takes 5 to 6 days at 25 to 27° C, the young medusa begins to pulsate quickly and swims away leaving behind the empty peridermal cup. The morphology of the young medusa is described.T. cystophora has a tricnidom of basitrich haplonemes, holotrich haplonemes, and heterotrich microbasic euryteles. The ecology of both, polyp and medusa generation, is briefly outlined. A critical comparison between the polyp and medusa ofT. cystophora and the Scyphozoa and Hydrozoa reveals important differences. Consequently, a new class, Cubozoa, must be established and given the evolutionary position between Scyphozoa and Hydrozoa. Diagnoses are presented for the polyp ofT. cystophora and the class Cubozoa.