Electron Microscopical Investigations on Two Loricate Choanoflagellates (Choanoflagellida), Calotheca alata gen. et sp. nov. and Syndetophyllum pulchellum gen. et comb. nov., from Indo-Pacific Localities

Calotheca alata gen. et sp. nov. and Syndetophyllum pulchellum gen. et comb. nov. are loricate choanoflagellates whose loricae are built up only from broad costal strips. The lorica of both taxa consists of two transverse costae and two sets of longitudinal costal strips. Syndetophyllum pulchellum further possesses a compound pedicel mostly formed by four diverging costal strips that are attached to the posterior lorica end. The most interesting new observation is the morphological adaptations towards linkage of costal strips to each other. In Calotheca alata one end of each anterior transverse costal strip is shaped so as to secure the neighbouring costal strip in a fixed position, whereas in Syndetophyllum pulchellum an anterior groove of each longitudinal costal strip helps to establish a firm contact between anterior transverse and longitudinal costal strips. Both taxa described offer points of resemblance with the recently established genus Stephanacantha, which is typifield by Stephanacantha campaniformis (formerly Parvicorbicula campaniformis). The locations at which Calotheca alata and Syndetophyllum pulchellum have been found suggest that both species are confined to warmer waters of full salinity. The known lower temperature limit of Calotheca alata is 15 degrees C, wheras that of Syndetophyllum pulchellum is 10 degrees C.