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Helicosphaera hyalina Gaarder 1970
Like H. carteri but coccoliths with closed central area (i.e. no pores) and usually smaller; also blanket is confined to central area leaving a broader rim of exposed flange elements than in H. carteri. The broad exposed rim is the most reliable criterion for distinguishing this species, since H. carteri coccospheres occasionally bear coccoliths without pores.

RANGE: ? to NN21

Description: Like H. carteri but coccoliths with closed central area (i.e. no pores) and usually smaller; also blanket is confined to central area leaving a broader rim of exposed flange elements than in H. carteri. The broad exposed rim is the most reliable criterion for distinguishing this species, since H. carteri coccospheres occasionally bear coccoliths without pores.

Remarks: H. hyalina has been regarded as a variety of H. carteri but culture studies and molecular genetics have shown that it is a discrete species (Geisen et al. 2004).

Range: Quaternary, possibly older.