Comparison of the two species on a sheltered shore on the Menai Strait, Wales.
Citrina L. fabalis at its smallest with thick aperture walls on the Fucus serratus (on left of image) is easily differentiated from olivacea, brown and citrina L. obtusata at its largest on the Ascophyllum. Unbiased samples can be obtained by shaking plants into a bucket. Note size overlap of adult (thick lip) L. fabalis with juvenile (thin lip) L. obtusata.
February 2011.
Full account at: 02 Differentiation L. obtusata/L. fabalis

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