Polyp dimorphism and functional, sequential hermaphroditism in the soft coral Heteroxenia fuscescens (Octocorallia)

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Abstract
Heteroxenia fuscescens is a dimorphic alcyonacean composed of autozooids and siphonozooids. The appearance of siphonozooids in the colony is size-dependent and their density gradually increases with colony diameter. Colonies in all size groups are simultaneous hepraphrodites and bear male and female gonads in their autozooids. H. fuscescens exhibits a size-dependent, functional, sequential hermphroditism in which mature monomorphic colonies produce only ripe sperm while dimorphic ones produce mainly eggs and relatively few sperm. Mature dimorphic colonies demonstrate a spatial segregation of reproductive products along the gastrovascular cavity. Germinative activity and extensive gonad growth of both sexes are carried out below the anthocodiae, mature eggs fill most of the gastrovascular cavity and fertilized eggs are very often observed in its basal part. Gametogeneis begins at a remarkably early age. However the size-dependent appearance of siphonozooids serves as a threshold, below which maturation and fertilization of eggs cannot occur. Reproductive effort in H. fuscesens is age-specific and exhibits an optimal allocation of energetic reserves which relates to polyp dimorphism.