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DescriptionLeptometra celtica has 10 slender pinnate arms up to 15 cm in length. Each arm (branchium) bears 2 rows of pinnules (appendages), with the first two pinnules being longer than the third. The centrodorsal plate (aboral plate) is conical or occasionally hemispherical and carries up to 45 long, slender, attachment cirri with the longest having 40-50 segments (joints). The cirral joints close to the centrodorsal are twice as long as they are broad, whereas those further away are as long as they are broad. This and the far dorsal edge being slightly swollen, gives the cirri a slightly scalloped appearance. The arms may be either brown, yellow, white or pinky-red in colouration or banded red and white. It's cirri are pure white.Leptometra celtica may be mistaken for Antedon bifida or Antedon petasus. Individuals have been observed to spread out their arms into a vertical fan across the current when in areas of moderate water flow. Antedon present at the same site was not observed to show this behaviour (Picton, 1993). Two annelid species of the genus Myzostoma have been associated with the arms and disc of this species (Southward & Campbell, 2006).