Larval biology and dispersal of Eudendrium racemosum (Hydrozoa, Eudendriidae)
Christian Sommer

In the life cycle of the Eudendriidae, a medusa is lacking and the planula-larva represents the only known dispersive stage. The importance of the planula for dispersal in Hydroida is mainly dependent on two variables: 1. the duration of the planktonic stage, and 2. any substratum-specifity shown by the larva at settlement. Eudendriid planulae are incapable of active swimming. Furthermore they differ from most other hydrozoan planulae by having an extremely high mucous secretion, which leads to the formation of a mucous thread. Many threads can stick together and form a conglomerate of slime-embedded larvae. Most planulae of Eudendrium racemosum settle and start metamorphosis 2.5 to 10 h after release. Under unfavourable conditions the attachment may be delayed for two or three days, after which the planulae stop moving and die. In choice experiments, planulae settled on a few species of algae, Eudendrium perisarc tubes, rocks, the shells of mussels, and crustacean cuticle. The behaviour of the planulae of E. racemosum is interpreted as a strategy leading to high densities of genetically different colonies.

Keywords: Eudendrium racemosum, larval biology, planula, dispersal, mucous thread.
Contents of this volume Sci. Mar. 56(2-3) : 205-211 Back PDF
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