Compare Orthoseira oregoniana

Compare

Orthoseira oregoniana is similar to taxa within the O. roeseana complex (Houk 1993). Briefly, group “tatrica” has spathulate spines while O. oregoniana has simple spines, group “epidendron” has many more carinoportulae (2–7), and group “dendrophila” is smaller (8–29 µm in diameter).

Orthoseira oregoniana is most easily confused with O. tropica and O. ursula due to the presence of ridge features near the margin. Note that O. oregoniana has been documented within the contiguous United States, while O. tropica and O. ursula have only been reported from South America. Orthoseira oregoniana striae begin to branch at the margin with the mantle, while the other two taxa have striae that begin to diverge on the valve face. Orthoseira ursula is larger (40–65 µm) and has additional structure or ornamentation in the space between carinoportulae.