Pelagic tunicates (Appendicularia and Thaliacea) of Sri Lanka: two first records with an annotated checklist

In broadening the understanding of the diversity, distribution and seasonality of gelatinous zooplankton of Sri Lanka, a survey ('Waya-jel-Survey) was carried out in coastal waters of the country from 2016 to 2020, and the collected specimens of pelagic tunicates were taxonomically identified. Further, a comprehensive literature survey was conducted and the previous records on the occurrences of pelagic tunicates within the exclusive economic zone of Sri Lanka were cross-checked and listed in developing the first-ever annotated checklist. Among the samples collected in this study, Pyrostremma spinosum and Thalia sibogae were reported for the first time from Sri Lankan waters while two more thaliaceans, i.e., Doliolum denticulatum and Pegea confoederata, and six appendicularians, i.e., Fritillaria borealis sargassi, F. formica digitata, Oikopleura cophocerca, O. fusiformis, O. longicauda, and O. rufescens were re-recorded. In total, forty species (including two subspecies) in 19 genera, belonging to five families from four orders of the classes Appendicularia (n = 17 species) and Thaliacea (n = 23 species) were reported to be inhabited in Sri Lankan waters. Most of the records were from the Laccadive Sea region while the majority of the species have been reported during the northwest monsoon (December to February) period.