Parasites and headless chaetognaths in the Indian Ocean
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Typhloscolecid polychaetes, assigned to the genera Typhloscolex (Typhloscolex muelleri) and Travisiopsis (Travisiopsis dubia), feeding on chaetognaths are reported for the first time from the Indian Ocean. These parasitic/predatory polychaetes cause decapitation in the chaetognath Flacisagitta enflata, either by eating the head or by causing injuries to the neck or body. Data from eastern Africa to western India showed a peak of polychaete infestation and decapitation of F. enflata in the Seychelles. A 5% peak occurrence (turnover rate is unknown) of decapitated individuals indicates that this parasitism/predation may have an important impact on local F. enflata populations. The harpacticoid copepod Microsetella norwegica was found feeding on the head and the reproductive organs of F. enflata. Therefore, this copepod may cause both decapitation and castration. Flatworm parasites are reported from the body cavity of F. enflata. Digeneans probably belonging to the genera Aphanurus, Parahemiurus, Accacladocoelium and Opechona, along with the accacoeliid Cercaria owreae and didymozoid metacercariae, were found. Cestode larvae were also recovered. No nematodes were found inside chaetognaths in this study.