Observations of Apparent Lorica Variability in Salpingacantha (Ciliophora: Tintinnida) in the Northern Pacific and Arctic Oceans

Abstract

Species identifications of tintinnid ciliates are based on characteristics of the lorica housing the ciliate cell. Molecular characterization of tintinnid ciliates has revealed the occurrence of cryptic species, genetically distinct forms with similar loricas, as well as polymorphic species in which genetically identical forms have distinct loricas. Among this latter category may be forms currently recognized as species of the genus Salpingacantha, erected by Kofoid and Campbell for forms originally described as varieties of species of Salpingella with ‘teeth’ on the margin of the lorica oral opening. Some workers have expressed the opinion that the genus is artificial and notably a recent molecular study suggested that Salpingella and Salpingacantha are likely synonyms. In this short communication we report on finding morphologically distinct loricas (containing ciliate cells) of Salpingacantha in single samples from stations in the North Pacific and Arctic Oceans in 2010, 2015 and 2016. We found up to 5 distinct Salpingacantha forms co-occurring, often with abundant Salpingella acuminata populations suggesting that some Salpingacantha species may be varieties of Salpingella acuminata. While we lack genetic data needed for definitive proof of polymorphism, here we document remarkable gradual gradients in morphology suggestive of polymorphism.