Modern Dinocyst Key

Cyst of Archaeperidinium constrictum Mertens et al., 2015

Characteristics:
Subsphaerical proximochorate cysts that are light brown in colour. Covered by numerous processes that have a very wide circular base. When cysts are covered with many processes the process bases contact each other. Processes are all of equal length but sometimes a few smaller processes can be present. Processes have very small captivated ends. Archeopyle is theropylic corresponding to plate 2a.

Dimensions: Cyst body: 28.1 to 47.6 µm diameter, Process length: mean: 3.8 to 6.4 µm, Process density: 19 to 37 processes 10 x 10 µm2.
Motile affinity: Archaeperidinium constrictum.
Stratigraphic range: Recent.

Comparison with other species:
Cysts most closely resemble cysts of Protoperidinium tricingulatum, Archaeperidinium minutum and Archaeperidinium saanichi. It differs from these species in having apiculocavate processes with a very wide basis with the basis often touching each other. This provides a very distinct regular (sun-drawing-like) appearance in light microscopic view.