OBSERVATIONS AND EXPERIMENTS ON METHODS OF FERTILIZATION IN THE CHAETOGNATH SAGITTA HISPIDA

¹ Rosenstiel School of Marine and Atmospheric Science, University of Miami, 10 Rickenbacker Causeway, Miami, Florida 33149

1. The first description is provided of the act of copulation of a planktonic chaetognath which leads to successful insemination and fertilization. It consists of a behavioral sequence in which partners maintain contact at their head ends while engaging in violent movements which result in the transfer of spermatophores.

2. Acts of self-insemination in the same species are also described, as well as experiments in which self-insemination and successful fertilization are induced.

3. The consequences of attachment of spermatophores to various parts of the body are described and compared to observations on the benthic genus Spadella.

4. Experiments showed 2% of batches of eggs laid by individuals isolated prior to maturity produced hatchings, suggesting that self-fertilization, although uncommon, does occur naturally.

5. Experiments indicated that one insemination was effective for only a single batch of eggs.

6. The similarities between copulation in Spadella and Sagitta are discussed and the possibility that self-fertilization presents a short-term survival mechanism for populations at low density is suggested.

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